• 专利附录
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    • 专利摘要:
    A method of simulating wave propagation wherein: a) providing data representing a three-dimensional scene (14); b) primary rays (Pij) emitted in different directions of propagation are calculated; d) according to a reception point (P), primary scattered radii (RdA, RdB) emitted by the surfaces of objects present in the scene reached by a primary ray are calculated. The power carried by the scattered rays (Rd) is calculated according to the relative orientation between the incident primary ray which reaches the surface of the considered object and the normal to this surface. Simulator, computer program and recording medium for the implementation of the method.
    公开号:FR3013867A1
    申请号:FR1361645
    申请日:2013-11-26
    公开日:2015-05-29
    发明作者:Steve Pechberti；Dominique Gruyer
    申请人:Institut Francais des Sciences et Technologirs des Transports de lAmenagement et des Reseaux；
    IPC主号:
    专利说明:

    [0001] The invention relates to a wave propagation simulation method, especially electromagnetic or acoustic. It is increasingly necessary to resort to simulation, whether for the development of new products, or for the qualification or certification of these. Indeed, in the case where a product interacts with waves, it may be necessary to simulate the propagation of these waves and their interaction with the product. The waves can in certain cases be produced by the product itself: this is the case for example for ultrasonic sensors, radars or lidars.
    [0002] This case therefore occurs especially during the development of radars or lidars embedded in vehicles. Such sensors are more often provided in vehicles to ensure the detection of obstacles and thus contribute to the achievement of active safety functions, assistance for driving or even automatic driving.
    [0003] State of the art With regard to radar simulation, the existing simulation methods are usually based, for real-time or semi-real-time applications, on launching a small number of radii, in a number of cases. limited directions and a restricted solid angle, the objects present in the scene being taken into account in a simplified way in the form of their Equivalent Surfaces Radar (SER). In addition, statistical models from test campaigns are sometimes also used for radar simulation.
    [0004] However, if the use of SER tables is often acceptable for aerial radars, for which the number of objects to be modeled is very small, conversely this method is inapplicable for radars embedded in land vehicles, whose environment near has a great variety of possible objects, and moreover movable relative to each other.
    [0005] Indeed, in such environments, the simulation of radar wave propagation on the basis of SER tables proves in practice insufficient, because it only makes it possible to manage relatively relatively grossly the masking of the elements and the phase shift induced by multiple bounces before the wave comes back on the air.
    [0006] The method therefore does not make it possible to simulate the waves received in return sufficiently close to reality. Accordingly, there is a need for a method for simulating the propagation of waves, in particular electromagnetic waves (in particular, waves outside the visible spectrum, and / or non-coherent waves). or acoustic, which is likely to provide a more realistic representation of simulated wave propagation than simulations using RESs. This objective is obtained thanks to the fact that the method comprises the following steps: a) providing scene data representing a three-dimensional scene comprising at least one object having a plurality of surfaces, each of said surfaces having a normal; b) calculating a plurality of primary rays emitted in respective propagation directions; each of said primary rays being defined at least by a transported power, a position, and a direction of propagation; d) according to a reception point, primary scattered rays are calculated, each of said primary scattered rays being emitted by a surface of said at least one object of the scene reached by a primary ray. A ray scattered by a surface reached by a ray, said incident ray, here means a ray emitted by the surface reached under the effect of the incident ray, having a direction of propagation passing through the receiving point, and having a power transported to the less a function of a relative orientation between the direction of propagation of the incident ray and the normal to the surface reached. The term 'radius calculation' here designates the attributes or parameters characteristic of this radius. The "position" of a ray can be in particular any information 25 defining the point of emission of this ray. It can be obtained through the attributes of the ray's point of emission. The simulation method thus makes it possible to determine the different rays received by an observer placed at a given point with respect to the scene, said receiving point. In a manner known per se, the method uses the technique of "ray tracing": the emitted wave is considered to be the union of a set of emitted rays, here called "primary rays". An important feature of the method is that during step d), radii scattered by the surfaces of the objects present in the scene are calculated. For these rays, the transported power is at least a function of the relative orientation between the direction of propagation of the incident ray and the normal to the surface reached (This relative orientation is subsequently called the "angle of incidence" of the ray on the affected area). Thus, step d) makes it possible to simulate the radiation perceived in return by the observer placed at the reception point by taking into account the geometry of the objects present in the scene, this geometry being taken into account by the fact that for each ray When the scattered beam is scattered, the power carried by the ray depends on the angle of incidence of the primary ray on the affected surface. The radiation perceived back to the point of reception is then the superposition or the sum of the rays diffused by the different surfaces of the objects of the scene in the direction of this point.
    [0007] Modeling objects In general, the objects present in the scene are recorded as a set of plane surfaces: the normal to the surface of the object reached by the incident ray is then simply the normal of the plane surface reached by the plane. incident ray. The flat areas may be plane facets, in particular triangular. Other types of modeling of the geometry of the objects present in the scene can in particular be envisaged, in particular by non-planar surfaces (for example defined by B-splines, Bezier curves, etc.).
    [0008] Modeling of the rays; ray / surface interaction The quality of the simulation performed also depends on the model chosen for the interaction between the incident ray and the surface reached by it. The predetermined model of interaction between an incident ray and a surface of an object defines the properties of the ray (s) possibly emitted by the surface, as a function of the properties on the one hand of the incident ray reaching the surface, and on the other hand from the surface. The ray or rays emitted by the surface are (exclusively) either scattered rays as defined above, or rays called "re-emitted" rays. The calculation of the emitted rays includes the calculation of various parameters.
    [0009] These parameters may notably include, for the emitted ray: its direction of propagation; its point of emission (this is the point of the surface reached by the incident ray); the energy or power carried by the emitted ray; the polarization of the emitted ray; the phase of the signal carried by the emitted ray; the distance traveled by the ray, since the emission of the original primary ray; the frequency of the signal carried by the ray emitted. They may also include, optionally, transverse shape characteristics of the radius, that is to say characteristics of the shape of a section of the radius in a plane transverse to its direction of propagation.
    [0010] The values of each of the parameters of the radius may vary as a function, on the one hand, of the path between the point of emission of the incident ray, and the point reached on the surface reached (in particular possibly as a function of parameters of the atmosphere between these two points) ; and secondly depending on properties of the surface reached by the incident beam. In particular, the power carried by a re-emitted ray may be at least a function of a relative orientation between the incident ray and the normal to the surface reached by it. Moreover, the properties of the scattered or re-emitted rays may depend not only on the relative positions or orientations of the incident ray with respect to the affected surface of the object, but also on the properties of the object itself. In one embodiment, a physical property of a material constituting a surface of an object of the scene is used to calculate the scattered rays.
    [0011] The property considered here may be a coefficient of reflection or transmission of the material of the affected surface of the object. For example, the property of the surface may in particular be defined by reflection coefficients, transmission, diffusion, the incident ray, or by the electrical and magnetic permeabilities of the material considered, which may be simple real numbers. The property of the surface can also be defined much more complex, being for example a function of the bidirectional reflectance distribution function (BDRF) of the material of the considered surface. . In this embodiment, it is therefore sufficient to assign certain parameters, certain properties to materials, and then to define that surfaces of objects present in the scene are constituted by the material or materials thus defined. For the calculation of a scattered ray, it is possible to take into account a predetermined model of interaction between an incident ray and a surface reached by it. For example, in one embodiment, and in the case where the waves are electromagnetic, in step d) the power or energy transported by the scattered ray (s) is calculated. using the integral electric field equation (EFIE). Advantageously, this equation makes it possible to calculate the properties of the scattered rays relatively simply.
    [0012] Steps a), b) and d) of the simulation method described above make it possible to efficiently simulate the propagation of rays in a three-dimensional scene. However, the simulation process can be made even more realistic by taking into account the multiple reflections of rays striking the scene. For this purpose, in one embodiment, the simulation method further comprises a complementary step c) during which: c) the propagation of incident rays is simulated, in particular iteratively, so that at each iteration, for each incident ray considered:. it is determined whether the incident ray, by propagation in a straight line, reaches a surface of an object of the scene; and. if according to a predetermined model of interaction between an incident ray and a surface of an object, at least one re-emitted ray (ray emitted by a surface of the scene, other than a scattered ray) is emitted after the interaction of said incident ray with said reached surface: the point reached on the affected surface is determined; and,. at least one radius re-emitted from the affected area is calculated; said incident rays considered being:. during the first iteration, the primary rays calculated in step b); . during each of the subsequent iterations, the re-emitted rays calculated at the previous iteration. In addition to step d), the scattered rays emitted by the surfaces of the object (s) of the scene reached by a re-emitted ray are further calculated. In this embodiment, the method may include one or more iterations in step c). Moreover, as for the scattered rays, it is possible to use a property, in particular a physical property of a material constituting a surface of an object of the scene to calculate the re-emitted rays. The re-emitted rays as defined in step c) may correspond to a transmitted wave or to a wave reflected by the object whose surface is reached by the incident ray. Other types of re-emitted rays can be considered, depending on the nature of the waves whose propagation is simulated. In step c), the determination of the point reached on the surface reached can consist in determining a point, defined by three-dimensional coordinates, or by two-dimensional coordinates on the surface reached. But this can also consist in a broader way in determining the area reached, or part of the area reached, since this operation is sufficiently precise to allow the calculation of the characteristics of the rays emitted as a result of the interaction of the incident ray with the element reached (point, surface portion, or area reached). Thus, in this mode of implementation of the method according to the invention, the ray tracing technique is implemented much more realistically than in the previous modes of implementation, in which the interaction between an object and an incident ray was modeled in a very simplified way by means of SER. Indeed, in step c), the calculation of the re-emitted radii makes it possible to obtain a much more accurate representation of the propagation of the waves.
    [0013] The re-emitted rays are generally calculated taking into account the geometry of the object or objects present in the scene. For example, one or more properties of the re-emitted rays may be a function of the normal of the surface reached. The normal of the reached surface of the object is naturally calculated at the point of the surface reached by the incident ray.
    [0014] In the case where the waves are electromagnetic waves, the model of interaction between the incident ray and the surface can be based on the equations of the physical optics. In this case, in one embodiment, the power transported by a re-emitted ray is calculated by the Snell-Descartes law.
    [0015] In order to calculate the propagation direction of the re-transmitted ray or radii, in one embodiment, the direction of propagation of at least one transmitted ray - and in general of each of the re-transmitted radii - depends solely on the direction of propagation of the incident ray and the normal of the surface reached. As a result of step c), and in the case where the rays are of electromagnetic nature, for each incident ray, only zero or a ray reflected by the surface (specular reflection) and possibly a ray transmitted inside are calculated. from the surface, if the surface is transparent. Then in step d), the radius scattered by the surface under the effect of the incident ray is calculated if necessary.
    [0016] Also, the process according to the invention is advantageously a process of substantially constant complexity; that is, the number of radii generally is relatively constant throughout the iterations. In fact, the incident rays which do not meet any surface do not give rise to any emitted ray; conversely, transparent surfaces (which generally form only a very small proportion of surfaces) can give rise to two re-emitted rays for an incident ray. In order to determine the frequency of an emitted ray calculated in step c), in one embodiment, a relative velocity of the area reached by the incident ray, relative to the reception point (II s) is taken into account. is a relative speed because the receiving point can possibly itself be driven by a clean speed).
    [0017] Data structure; calculation means: GPU In addition to the physical parameters that govern the propagation of the rays studied, the choice of certain specific calculation means makes it possible to implement the method in a particularly efficient manner. In particular, particularly because of the choice of the ray tracing algorithm for the propagation of the emitted wave, the method can advantageously be implemented on a graphics card. Thus, in a particularly advantageous embodiment of the invention, step c) and / or step d) is performed on a (single) graphics card (CGU), and the calculations made for each of the rays are made in parallel.
    [0018] This embodiment therefore makes it possible to carry out the calculations of step c) and / or d) in a particularly rapid manner. Thanks to this, advantageously the method can be implemented in real time or semi-real time. To implement the method on a graphics card as indicated above, the scene data is preferably composed mainly of at least one multidimensional matrix, or a set of three-dimensional individual data. In the first case, the geometry of objects is not saved as three-dimensional coordinates. The position of the objects, on the other hand, is recorded as the coordinates (line number and column number) of a datum in a matrix, as well as in the form of a depth value usually named 'z'. The geometry is stored in one or more matrices usually called "Z-buffer". This or these matrices containing the geometry information of the objects of the scene are part of the scene data, recorded in a multi-dimensional matrix, also called 'G-buffer' (buffer or graphic buffer). By "multi-dimensional" matrix is meant here a set of matrices having the same number of rows and columns. Advantageously, a multi-dimensional matrix makes it possible to store, for the same position (i, j) in the multi-dimensional matrix, not only a scalar information (such as a depth information in 'z'), but a number any information relating to the element referenced at the location (i, j). In the second case, on the contrary, the geometry is recorded as three-dimensional data. In this case, the scene data mainly comprise entities that contain the three-dimensional coordinates of the different surfaces of the objects contained in the scene. They may furthermore comprise other data, recorded for example in multidimensional matrices, in particular the different coefficients characterizing the surfaces of the objects of the scene. In addition, just as the scene can be recorded in a multi-dimensional matrix, advantageously the (primary, and / or broadcast, and / or re-transmitted) rays can be as well. Thus, in one embodiment, the primary rays, the re-emitted rays, and / or the scattered rays are recorded in a multidimensional matrix. Preferably in step c) the propagation direction of the re-transmitted rays is calculated using scene data and incident ray characteristics, without involving other data representing the geometry of the scene. Furthermore, in one embodiment of the method according to the invention, the calculations required in step c) and / or d) can be programmed on a multiprocessor graphics card by means of "shaders". A shader is a program, written in a language - either assembly language or a higher level language - directly executable by a graphics processing unit (GPU) and which replaces parts of the pipeline. usual execution. It is possible in particular to use shaders programmed in GLSL ("openGL Shading Language"). The use of "shaders" imperatively requires the recording or modeling of the data or information in the form of multidimensional matrices, which then makes it possible to process them by "shaders" in a massively parallel manner, in a space called "image space" . This programming mode is therefore particularly adapted to the case where the scene and / or the rays (primary, re-transmitted, and / or scattered) are represented by multidimensional matrices (that is to say by a G-buffer as presented above). In another embodiment, the computations required in step c) and / or d) can be programmed on a multiprocessor graphics card using a multiprocessor graphics card programming language allowing direct access to the instructions and the control. memory of the different parallel computing processors of the graphics card, such as the programming language Cuda (registered trademark).
    [0019] This programming mode can in particular be chosen when the scene is represented - in the form of three-dimensional data. Simulation of Sensors A particularly important application of the wave propagation simulation method according to the invention is the simulation of sensors. The invention thus also relates to a method of sensor simulation, in particular of a sensor for a motor vehicle, the sensor being provided for transmitting waves and for producing an output signal as a function of waves received in return following said transmission. method, the method comprising the following steps: i) simulating the wave emission by the sensor, and the propagation of said waves, so as to determine the rays received by the sensor, by implementing a simulation method of wave propagation as defined above; and ii) determining the output signal of the sensor as a function of the radii received by the sensor and predetermined characteristics of the sensor. The sensor simulation is done first by simulating the emission of waves by the sensor, then their propagation (step i). During the wave propagation simulation at this step i), the propagation of the waves is simulated so as to calculate the scattered rays that will be received by the sensor placed at the reception point. The output signal of the sensor is then calculated as a function of the characteristics of the sensor. This calculation can be done in different ways. In one embodiment, the output signal of the sensor is determined in step ii) by performing the following two steps e) and f): e) the respective signals of at least a portion of said scattered rays are calculated ; and f) calculating a signal received at the reception point by summing the respective signals calculated in step e2).
    [0020] The output signal of the sensor is then determined according to the signals of the different scattered rays returned by the scene and received by the sensor at the reception point. In particular, to limit the calculation times, it is desirable to calculate the signals carried by the scattered rays only for a reduced number of scattered rays. For this purpose, preferably, step e) comprises the following two sub-steps: el) a subset of scattered rays is selected according to a predetermined criterion, in particular a criterion taking into account the transmitted power of the scattered rays and / or at least one neighboring ray characteristic such as a total distance traveled and / or a phase of the transported signal; e2) the respective signals of the selected scattered rays are calculated only for the selected subset of scattered rays. Typically, in step e), the selection of the subset of scattered rays is made by sorting the scattered rays in order of power or energy transported.
    [0021] However, the respective signals of the different scattered rays may possibly be calculated for all the scattered rays. The addition of the respective signals of the different scattered rays takes into account the respective characteristics of the scattered rays so as to produce a cumulative signal representative of reality. Different parameters can be taken into account to increase the quality of the simulation. In one embodiment, for each re-emitted ray calculated in step c), a distance traveled by the ray from the emission point of the primary ray that generated the reemitted ray considered is determined. This allows in particular step f) to calculate for each selected scattered ray the power of the signal received by the sensor, taking into account the total distance actually traveled by the scattered ray, and consequently the power loss (expressed by example in dB) which follows.
    [0022] The quality of the simulation can be further improved by adding noise to the respective signals of the different selected scattered rays, and / or to the received signal thus calculated. The quality of the simulation can also be improved by taking into precise account the operation of the sensor wave antenna (The term 'antenna' is used here to designate any wave transmission system that includes the sensor). In one embodiment, in step b), a transmission diagram is provided indicating energy losses as a function of the direction of propagation; and the power carried by the primary rays is calculated according to the emission diagram. The emission diagram thus makes it possible to realistically take into account the actual transmission properties of the sensor antenna.
    [0023] The invention also relates to a method for simulating a motor vehicle comprising at least one sensor, in which propagation of waves transmitted and / or received by the sensor is simulated by implementing a wave propagation simulation method. as defined above, in particular a method in which the sensor is simulated by the sensor simulation method as defined above. The invention also relates to a computer program comprising instructions for executing the steps of one of the simulation methods defined above.
    [0024] The invention also relates to a computer-readable recording medium on which is recorded a computer program comprising instructions for executing the steps of one of the simulation methods defined above. Finally, the invention also relates to a wave propagation simulator, comprising: a) a memory, capable of storing scene data representing a three-dimensional scene comprising at least one object having a plurality of surfaces, each of said surfaces having a normal; b) primary calculation means, capable of calculating a plurality of primary rays emitted in respective propagation directions; each of said primary rays being defined at least by a transported power, a position, and a direction of propagation; d) scattered ray calculation means, able to calculate as a function of a reception point of the primary scattered rays, each of said primary scattered rays being emitted by a surface of said at least one object of the scene reached by a primary ray; a ray diffused by a surface reached by a ray, said incident ray, being a ray reflected by the surface reached under the effect of the incident beam, having a direction of propagation passing through the receiving point, and having a transported power of at least function of a relative orientation between the incident ray and the surface normal reached. In one embodiment, this simulator further comprises: c) means for calculating re-transmitted radii adapted, in particular iteratively, to each iteration and for each incident ray considered: to determine if the incident ray, by propagation in straight line, reaches a surface of an object of the scene; and. if, according to a predetermined model of interaction between an incident ray and a surface of an object, at least one re-emitted ray is emitted after the interaction of said incident ray with said reached surface: to determine the point reached on the affected surface; and. calculating said at least one re-emitted ray from the affected area; said re-transmitted ray calculating means being arranged to take into consideration as incident rays: during the first iteration, the primary rays calculated in step b); . during each of the subsequent iterations, the re-emitted rays calculated at the previous iteration 10. In addition, the means for calculating scattered rays are able, in step d), to calculate scattered rays emitted by the surfaces of said at least one object of the scene reached by a re-transmitted ray. The invention will be better understood and its advantages will appear better on reading the following detailed description of embodiments shown by way of non-limiting examples. The description refers to the accompanying drawings, in which: - Figure 1 is a schematic view of a road on which three vehicles evolve; FIG. 2 is a schematic view showing a data structure making it possible to record the geometry of a scene; FIG. 3 is a schematic view showing the interaction of an incident ray with a surface of an object; FIG. 4 is a schematic view from above showing the propagation of primary rays projected by the radar in the scene of FIG. 1; FIG. 5 is a diagrammatic view from above showing the propagation of re-emitted rays emitted by the vehicles present in the scene of FIG. 1 after reception of the primary rays; FIG. 6 is a diagrammatic view from above showing propagation of rays scattered by the vehicles present in the scene of FIG. 1 after reception of the primary rays; FIG. 7 is a schematic view of a signal carried by a radar beam; FIG. 8 is a schematic view of a signal received by the radar; and FIG. 9 is a schematic representation of the wave propagation simulation method according to the invention.
    [0025] An embodiment of the method and the device according to the invention will now be described with reference to the figures. In the embodiment shown, the wave propagation method is a method of propagating electromagnetic waves, used to simulate the operation of an on-board radar on a motor vehicle, for example a car. Such a radar is typically implemented in a scene such as that shown in Figure 1. In this figure are shown three cars A, B, C traveling on a road 10. The car C is equipped with a radar 12. The latter emits from a point P (more precisely, from an area considered substantially punctual) electromagnetic radiation. The part of this radiation which is exploited is that which propagates in the solid angle S represented in FIG. 1. This solid angle S divides itself into a matrix of elementary solid angles Su where i denotes the line and varies from 1 to n, and j denotes the column and varies from 1 to p. The part of the space included in the solid angle S, and limited on the front side of the car C by a plane L situated at a predetermined distance from the car C (in practice, at about 200 meters from it) constitutes a scene 14. The function of the radar 12 is to detect obstacles within this scene. In a first step, the main steps of the ray propagation simulation method according to the invention will be presented in relation with FIG. 9. This figure presents the radar simulation as a peripheral process of a main process which is the operating simulation of a motor vehicle. The circulation of the car C on the road 10 is simulated by a simulator of a motor vehicle 100. This simulator 100 comprises a central computer 102 which executes a computer program 104 for vehicle simulation, called the 'simulation engine'. This program 104 simulates the movement of a vehicle, and in this particular case, the movement or movement of the car C. For this, the program 104 simulates the acquisition of the various information acquired by the sensors of the car C. It therefore simulates, in particular, the acquisition of the information provided by the radar 12. This latter simulation (radar simulation) is carried out by a radar computer 110. This comprises a central unit 112 with a main processor and a storage memory. , as well as a graphics card 114.
    [0026] The program 104 operates iteratively, with a real-time or semi-real-time processing loop simulating the evolution of the circulation at regular intervals, for example 40 ms (in real time). At each processing loop, the program 104 transmits to the radar calculator 110 the geometric description CG ', Fig. 9) of the scene which is in front of the radar 12 at the instant in question. This description includes the relative velocities relative to the radar 12 of the different objects present in the scene. In the graphics card is recorded a treatment program also noted 114.
    [0027] The graphics card executes the program 114 so as to carry out the following processes: a) On receiving the data relating to the scene 14, the program 114 constitutes scene data representing the scene placed in front of the radar 12; b) the program 114 then performs a 'ray firing', and thus calculates the characteristics of the different primary rays that are emitted by the radar; c) iteratively, the program 114 simulates the propagation of incident rays in the scene 14. These incident rays are: during the first iteration, the primary rays emitted by the radar; and. during each of the subsequent iterations, the re-emitted rays calculated at the previous iteration. Also, at each iteration and for each of the incident rays, the program 114 determines whether the incident ray, by propagation in a straight line, reaches a surface of an object of the scene. If this is the case, the program 114 then determines whether one or more rays are re-emitted after the interaction of the incident ray considered with the area reached. The emission of one or more rays after this interaction, and the characteristics of the re-emitted rays, are determined according to the interaction model between an incident ray and a surface of an object, which is chosen in advance. . The program 114 thus determines, on the one hand, the point reached on the surface reached; and, on the other hand, the characteristics of the rays or rays emitted from the surface reached under the effect of the incident ray considered. d) the program 114 calculates the rays diffused by the different surfaces present in the scene 14 towards the point of reception, that is to say here towards the radar 12; el) the program 114 selects a subset of scattered rays according to a predetermined criterion taking into account the power or energy transported of the scattered rays; it then transmits this information to the central unit 112 of the computer 110. In the central unit is recorded a processing program also denoted 112. The program 112 carries out the following processes: e2) the program 112 calculates signals respectively for each of the scattered rays selected in step e1). f) the program 112 calculates a signal received by the radar by adding the respective signals calculated in step e2). It then calculates the output signal Sr of the radar according to the signal received by the radar. a) Scene data To simulate the operation of the radar 12, scene data representing the scene 14 is first used or created.
    [0028] These data comprise at least a set of geometric data including in principle any object present in the scene, provided that it is of sufficient size to be detectable in an elementary solid angle Si. For each object, the scene data therefore comprise , for its different surfaces may be illuminated by a ray emitted by the radar, a simplified description of the surface, including in particular the coordinates of the vector normal to the surface. The scene data also preferably include different coefficients or parameters characterizing the surface (or the material constituting the surface) and used for calculating the re-emitted rays following the interaction of an incident ray with the surface. These coefficients can be in particular coefficients characterizing the properties of the surface relating to the reflection, the transmission and the scattering of incident rays.
    [0029] These coefficients may be for example refractive indices, a thickness, a roughness ... In addition, the scene data may include, for each surface, the indication of the instantaneous speed of the surface relative to the radar.
    [0030] These different coefficients are generally recorded by a reference to the material constituting the surface. In this case, for each material constituting a surface of the objects present in the scene 14, coefficients are recorded characterizing the response of the material when a surface constituted by this material receives an incident ray, this incident ray having the frequency and the form of wave produced by the radar whose operation is simulated. The scene data is stored in the memory of the graphics card 114.
    [0031] They can be recorded in different ways. In the embodiment presented here, they are recorded in the form of a multidimensional matrix M (FIG. 2), also called in graphics "Gbuffer" or "Graphics-buffer". The matrix M has the same number of rows and columns as the matrix of elementary solid angles; but it consists of a number (q) of individual matrices, denoted M1, M2, ... Mg. Thus, the location of each surface of an object of the scene is recorded only on the one hand, via the components (i, j) of the matrix element in which the surface is recorded, and on the other hand by a depth information 'z', which is stored in the matrix M, for example in the matrix M1. It is therefore a Z-buffer. The following matrices M2, M3, ... Mu serve to record the other properties of the surface (these properties are recorded in this example by u-1 real numbers). These other properties may consist of the indication of the material constituting the surface, the properties of this material being recorded elsewhere.
    [0032] If in a given solid elementary angle, the scene comprises several successive surfaces at increasing distances from the point P, these different surfaces are recorded in the matrix M, in individual matrices Mk, where k begins for example at the value u + 1. Alternatively, the scene data can be recorded as a three-dimensional scene comprising objects themselves composed of a set of facets, in particular triangular facets, surface properties being associated with the facets in particular in the form of textures, by means of coordinates. texture in a manner known per se. b) Calculation of the primary rays The simulation of the operation of the radar first requires calculating the rays emitted by the radar from the emission point P (primary rays).
    [0033] To simplify the calculation, a primary radius Pu is calculated for each elementary solid angle S. The primary rays are thus recorded in a multidimensional matrix similar to the matrix M previously described. Figure 4 schematically shows the primary rays Pu emitted on a horizontal line of solid angles Su. For each primary ray Pu are recorded the following information: - its direction of propagation (It is recorded implicitly by the coordinates (i, j) of the radius P1 considered); - its point of emission (for the primary rays, it is the point P); - the power carried by the emitted beam. This information is recorded as a gain - negative - in dB relative to the initial maximum power of a primary beam; - the polarization of the primary ray; - the phase of the signal carried by the primary ray; - the distance traveled by the ray since the emission of the primary ray of origin (zero distance, in the case of primary rays); - the frequency of the signal carried by the primary ray. - Doppler coefficient associated with the primary ray (zero coefficient in the case of primary rays).
    [0034] The gain value is not the same for all primary rays. Indeed, for each primary beam, the gain is provided by the emission diagram of the transmitting antenna of the radar 12. This antenna diagram indicates, as a function of the elementary solid angle Su, the energy or the effective power - and thus the gain of the radius that the radar emits in the elementary solid angle. It is therefore this value that is recorded as initial gain for each primary ray. In practice, the gain of the primary rays is high in the center of the beam emitted by the radar, and lower on the sides. c) Radiation propagation Radiation propagation is based on a model of interaction with the known surface (Fig.3). According to this model, as a function of parameters of reflection, transmission and diffusion of the surface, when an incident ray RI strikes a surface at a point E, it can be absorbed without emission of any radiation; it can give rise to a reflected ray Rr; it can give rise to a transmitted ray Rt. The characteristics of these different rays depend each on the direction of incidence (and therefore on the direction of propagation of the incident ray) and of the normal n on the surface.
    [0035] On the other hand, radiation can be scattered from the point E in the receiving direction (which may be the direction of emission of the primary rays); there is then projection of a scattered ray Rd in the direction of the point P. Moreover, in this mode of implementation the interaction of the incident ray with the affected surface rests on the following assumptions: It is considered that the incident ray is has as a monochromatic plane wave, and this even if the signal carried by the incident ray (for example, in modulated radars FMCW, FSK, pulse, ...) is actually the superposition of several monochromatic waves.
    [0036] It is further considered that when an electromagnetic wave front interacts on the surface of an object (or at the interface between two media), this surface is considered locally as plane and is considered to be an infinite plane for the calculation of the emitted radius. (However, the calculation may take into account the curvature of the surface).
    [0037] An example of an interaction of the primary rays with the objects of the scene is illustrated in Figures 4 to 6. In one of the primary ray emission planes Pu (j = Cte), illustrated in Figure 4, the primary rays hit the vehicle A in three basic solid angles and the vehicle B also in three basic solid angles (arrows in bold, Fig.4). For each primary ray Pu, during the first iteration of the program 114 in step c), the interaction of the different primary rays Pu with the surfaces of the objects present in the scene is evaluated. It should be noted that the interaction with the ground constituting the road 10 should normally be taken into account; however, to simplify the explanations this interaction is not discussed in the example presented. On the vehicle A, the surfaces reached are opaque surfaces located at the rear of the vehicle; no ray is transmitted through the surface. On the other hand, these surfaces give rise to three reflected rays re-emitted RrA- On the vehicle B, the surfaces reached are the transparent surfaces of the front windshield of the vehicle. These surfaces give rise at first to three reflected rays re-emitted Rrg. Being transparent, they also give rise to three transmitted rays re-emitted RtI3. The evaluation of the interaction between the primary rays (or, at the subsequent stages of computation, the incident rays) and the surfaces of the objects of the scene thus leads to the creation of new rays, the re-emitted rays RrA, Rr13 / RtB . These rays do not have the same characteristics as the primary rays. Their characteristics are calculated in the following way: - the direction of propagation is calculated according to the model of interaction with the surface considered, according to the direction of the incident ray and the normal direction of the surface at the point struck by the incident ray ; the point of emission of the re-emitted ray is the point of the surface struck by the incident ray; the gain and the polarization of the re-emitted ray are calculated according to the interaction model with the surface considered, as a function of the characteristics of the surface, and possibly as a function of the direction of the incident ray and the normal direction of the surface at the point struck by the incident ray; the phase of the signal carried by the re-emitted ray, and the distance traveled by the ray from the emission of the original primary ray, are calculated according to the position of the struck point on the surface, with respect to the radar, and optionally depending on properties of the surface; and the frequency of the signal carried by the re-emitted ray is calculated as a function of the relative velocity of the surface relative to the radar. An important parameter is the gain of the re-emitted ray, which corresponds to the power of the signal carried by the ray. The program 114 calculates the gain of the re-emitted rays using the equation of the physical optics: The power transported by a re-emitted ray is calculated by the Snell-Descartes law. Naturally, a large number of primary rays do not encounter any surface of an object of the scene 14; they do not give birth to any ray emitted. In step c), after the first interaction of each of the primary rays with the surfaces of the objects of the scene 14 has been evaluated, the program 114 can perform one or more iterations so as to calculate one or more subsequent interactions between the rays. re-emitted and the surfaces of the objects of the scene. In the example presented, however, the program 114 is set to go to step d) as soon as the second iteration of step c) has been performed, that is to say as soon as all the primary rays have reached the areas they can reach by propagation in a straight line from the point P. More generally, the program 114 can be set to go to step d) either after a fixed number of iterations or when another criterion has been reached. Optionally, step c) may not be performed. Program 114 goes directly from step b) to step d).
    [0038] The calculations are performed in a massively parallel manner on the graphics card 114. The number of primary rays is chosen so as to generate a number of rays that can be processed by the graphics card at the desired processing frequency. d) Calculation of the scattered rays In step d), the program 114 calculates the rays scattered by the different surfaces present in the scene 14 in the direction of the radar 12. This calculation is done for each of the surfaces of the scene 14. surface may possibly give rise to several emitted rays (scattered or re-emitted) if it is reached by several incident rays, in particular during several iterations carried out in the propagation step c). In the example presented, step c) is stopped at the end of the first iteration.
    [0039] The program 114 thus calculates six scattered rays: three radii distributed by the rear wall of the car A, and three rdb radiated by the front wall or the side wall of the car B. The program 114 does not calculate radius Rdg for the other surfaces of car B, because at the end of the first iteration (Fig.5), only the front wall and side wall of car B were hit by incident rays (Since this is the first iteration, the incident rays are the primary rays Pu). For each surface of the scene 14, the program 114 calculates the scattered ray (s) (if any) emitted by the surface, taking into account all the incident rays having reached the surface considered at course of the different iterations of step c). The scattered rays have substantially the same parameters as the primary rays. el) Sorting and selection of scattered rays Next in step e1), the program 114 selects a subset of scattered rays according to a predetermined criterion taking into account the power carried by the scattered rays. This criterion is based more precisely on the power returned to the antenna, which is a function of the power carried by the scattered rays.
    [0040] The power returned to the antenna by a scattered ray is calculated on the basis of characteristics of the radar receiving antenna 12, in particular the dimensions or the surface thereof. It is possibly calculated according to the gain of the antenna, this gain being able to depend on the direction of origin of the diffused ray. More concretely, this power is calculated on the basis of the integral equation of the electric field, by integrating the flux of the Poynting vector of the scattered ray through the surface of the antenna. The calculation for each ray broadcast of the power returned to the antenna by the ray diffused makes it possible to proceed to the selection of the scattered rays which will be taken into account for the calculation of the signal actually received by the radar. Indeed, this selection consists in practice to take into account in the following calculations only the rays that will return a significant power to the radar. For this purpose, we begin by sorting the scattered rays as a function of the power returned to the antenna by each; then, only the scattered rays of higher power returned to the antenna are retained. This selection work makes it possible to reduce the amount of data to be transmitted to the central unit 112 of the radar calculator 110, and this substantially without any loss of performance for the simulation, insofar as the scattered scattered rays are rays whose contribution to the radar signal is very small and thus negligible. According to a variant, always in order to limit the amount of information sent back by the GPU-accelerated RADAR propagation channel simulator, the scattered rays are selected in the following manner: First, groups of rays having similarities in terms of position, total distance traveled by the beam, phase shift, and / or frequency. Such a grouping of the rays can be achieved by partitioning algorithms (in English: "clustering") directly on the graphics card and in parallel manner, by the program 114. Each group of scattered rays is then characterized by the characteristic statistical values of the group: mean and variance of the total distance traveled, mean and variance of the phase shift, average and variance of the reception direction, total power. In this case, to select a part of the scattered rays, the groups of rays of greater importance are selected. The isolated rays, or small groups are assimilated to radar noise (English: clutter) and thus eliminated.
    [0041] We can also make the selection by taking into account, possibly in addition to the criteria mentioned above, the total distance traveled. For example, one can select only the N radii (N is an integer) with the smallest total distance traveled before returning to the point of reception.
    [0042] The information corresponding to the groups of selected rays can then be transmitted to the program 112 of the radar calculator 110 in a synthetic manner, by transmitting only aggregated values corresponding to the groups of selected rays. e2) Calculations of the signals of the scattered rays The data relating to the scattered rays thus selected are then transmitted to the central unit 112 of the radar calculator 110. Upon receipt of this information (step e2)), the program 112 calculates a signal Sd for each of the selected scattered rays. This signal is calculated on the basis of the signal initially emitted by the radar, as represented by FIG. 7. The respective signals Sd thus generated for the various selected scattered rays are calculated on the assumption that the primary rays are emitted during a period of time. same time period between instants 0 and T. The duration T is chosen so as to be large compared to the phase shifts induced by the differences in the flight distance between the different radii (the scales in FIGS. 7 and 8 are not representative ). Although FIG. 7 represents a sinusoidal signal at a constant frequency, it is understood that the method can be used with any type of radar signal, in particular signals of variable frequencies, continuously or in steps for example (FSK, FMCW, etc.) . The individual signals corresponding to each of the scattered rays have a shape close to the initial radar signal, for example in the present case, a sinusoidal shape.
    [0043] However, they are modified with respect to the initial signal taking into account in particular the following parameters of the scattered ray: the phase of the ray; the energy or power carried by the beam (or the power returned to the antenna), the polarization of the beam, if any, the distance traveled by the beam since the emission of the primary beam; the frequency of the signal carried by the ray. f) Calculation of the Signal Received by the Radar and the Radar Output Signal Then, in step f), the program 112 calculates the signal Sr received by the radar by adding the respective signals Sd of the different selected scattered radii calculated at step e2). This calculation takes into account reception parameters specific to the radar itself, that is to say receiving antenna parameters.
    [0044] On the basis of the signal Sr received by the radar, the program 112 then calculates the output signal of the radar Ss. The output signal of the radar Ss thus obtained is then transmitted to the program 104 of simulation of vehicle displacement (FIG. .
    [0045] This signal Ss can then be the subject of further processing, then be merged with other information acquired by other sensors of the vehicle to feed, for example, a program automatically determining the commands to be applied to the vehicle to ensure steering or the conduct of it.
    [0046] Finally, although the example presented, a radar having a single antenna for transmission and reception has been used, the invention can be implemented with a plurality of ray sources. It can also be implemented by evaluating the scattered rays (step d)) not for a single receiving position, but for several receiving positions. In the example presented, the graphics card 114 constitutes both the primary calculation means, the means for calculating scattered rays, and the re-transmitted ray calculation means, in the sense of the invention.
    权利要求:
    Claims (17)
    [0001]
    REVENDICATIONS1. A method of simulating wave propagation, in particular electromagnetic or acoustic waves, wherein: a) providing scene data representing a three-dimensional scene (14) having at least one object (A, B) having a plurality of surfaces each of said surfaces having a normal; b) calculating a plurality of primary rays (P11) emitted in respective propagation directions; each of said primary rays being defined at least by a transported power, a position, and a direction of propagation; the method being characterized in that it further comprises a step d) in which: d) as a function of a reception point (P), primary scattered radii (RdA, RdB) are calculated, each of said primary scattered radii being emitted by a surface of said at least one object of the scene reached by a primary ray; a ray diffused (Rd) by a surface reached by a ray, said incident ray, being a ray emitted by the surface reached under the effect of the incident ray, having a direction of propagation passing through the receiving point, and having a power transported at least a function of a relative orientation between the incident ray and the normal (n) at the reached surface.
    [0002]
    The propagation simulation method according to claim 1, wherein the scene data consists mainly of at least one multidimensional matrix (M), or a set of three-dimensional individual data.
    [0003]
    A propagation simulation method according to claim 1 or 2, in the case where the waves are electromagnetic, wherein in step d), the power carried by the at least one scattered ray is calculated using the integral equation. of the electric field.
    [0004]
    4. Propagation simulation method according to any one of claims 1 to 3, further comprising a complementary step c) during which: c) the propagation of incident rays is simulated, in particular iteratively, in such a way that at each iteration, for each incident ray considered:. it is determined whether the incident ray, by propagation in a straight line, reaches a surface of an object of the scene; and. if according to a predetermined model of interaction between an incident ray and a surface of an object, at least one re-emitted ray (RrA, RrgiRtg) is emitted after the interaction of said incident ray with said reached surface: the point reached on the affected surface is determined; and,. at least one radius re-emitted from the affected area is calculated; said incident rays considered being:. during the first iteration, the primary rays calculated in step b); . during each of the subsequent iterations, the re-emitted radii calculated at the previous iteration; a method in which: in step d), scattered rays emitted by the surfaces of said at least one object of the scene reached by a re-transmitted ray are furthermore calculated.
    [0005]
    The propagation simulation method according to claim 4, wherein at least one property of at least one re-emitted ray is a function of the normal (n) of the reached surface.
    [0006]
    The propagation simulation method according to claim 4 or 5, wherein the direction of propagation of each of the re-emitted rays depends solely on the direction of propagation of the incident ray and the normal (n) of the reached surface.
    [0007]
    7. Propagation simulation method according to any one of claims 4 to 6, in the case where the waves are electromagnetic, wherein the power transported by a re-emitted ray is calculated by Snell-Descartes law.
    [0008]
    8. A propagation simulation method according to any one of claims 1 to 7, wherein step c) and / or step d) is performed on a single graphics card (114), and calculations made for each rays are made in parallel.
    [0009]
    The propagation simulation method according to any one of claims 1 to 8, wherein the primary rays, the re-emitted rays, and / or the scattered rays are recorded in a multidimensional matrix.
    [0010]
    The propagation simulation method according to any one of claims 1 to 9, wherein a property of a material constituting a surface of an object of the scene is used to calculate the re-emitted rays and / or the rays. disseminated.
    [0011]
    11. A method for simulating a sensor (12), particularly a sensor for a motor vehicle, the sensor being provided for transmitting waves and for producing an output signal as a function of waves received in return following the transmission transmitted waves, the method comprising the following steps: i) the emission of waves by the sensor, the propagation of said waves, is simulated so as to determine the rays received by the sensor, by implementing a method according to FIG. any one of claims 1 to 10; and ii) determining the output signal (S5) of the sensor as a function of the radii (Rd) received by the sensor and predetermined characteristics of the sensor.
    [0012]
    The method of simulating a sensor according to claim 11, wherein, to determine the output signal of the sensor in step ii), steps e1, e2 and f are performed in which: a subset of scattered rays (Rd) is selected according to a predetermined criterion, in particular a criterion taking into account the transmitted power of the scattered rays, and / or at least one characteristic of neighboring rays such as a total distance traveled. and / or a phase of the transported signal; e2) the respective signals of the selected scattered rays are calculated only for the selected subset of scattered rays; and f) calculating a signal received at the reception point by summing the respective signals calculated in step e2).
    [0013]
    13. The method of simulating a sensor according to claim 11 or 12, wherein in step b), an emission diagram is provided indicating energy losses as a function of the direction of propagation; and the power carried by the primary rays is calculated according to the emission diagram.
    [0014]
    A computer program comprising program code instructions for executing the steps of the simulation method according to any one of claims 1 to 13 when said program is executed on a computer.
    [0015]
    15. A computer-readable recording medium on which a computer program is recorded including instructions for executing the steps of a simulation method according to any one of claims 1 to 13.
    [0016]
    A wave propagation simulator comprising: a) a memory adapted to store scene data representing a three-dimensional scene having at least one object having a plurality of surfaces, each of said surfaces having a normal; b) primary calculation means (114), able to calculate a plurality of primary rays emitted in respective propagation directions; each of said primary rays being defined at least by a transported power, a position, and a direction of propagation; d) scattered ray calculation means (114), able to calculate as a function of a reception point of the primary scattered rays, each of said primary scattered rays being emitted by a surface of said at least one object of the scene reached by a primary ray; a ray diffused by a surface reached by a ray, said incident ray, being a ray reflected by the surface reached under the effect of the incident beam, having a direction of propagation passing through the receiving point, and having a transported power of at least function of a relative orientation between the incident ray and the normal (n) at the reached surface.
    [0017]
    17. The simulator according to claim 16, further comprising c) means for calculating re-transmitted radii (114) able, in particular iteratively, at each iteration and for each incident ray considered: to determine if the incident ray, by propagation in a straight line, reaches a surface of an object of the scene; and. if, according to a predetermined model of interaction between an incident ray and a surface of an object, at least one re-emitted ray is emitted after the interaction of said incident ray with said reached surface: to determine the point reached on the affected surface; and,. calculating said at least one re-emitted ray from the affected area; said re-transmitted ray calculating means being arranged to take into consideration as incident rays: during the first iteration, the primary rays calculated in step b); . at each subsequent iteration, the re-emitted rays calculated at the previous iteration; the means for calculating scattered rays being furthermore capable, in step d), of calculating scattered rays emitted by the surfaces of said at least one object of the scene reached by a re-emitted ray.
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    同族专利:
    公开号 | 公开日
    EP3074892A1|2016-10-05|
    FR3013867B1|2017-11-24|
    WO2015079152A1|2015-06-04|
    US20170132335A1|2017-05-11|
    US10133834B2|2018-11-20|
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    优先权:
    申请号 | 申请日 | 专利标题
    FR1361645A|FR3013867B1|2013-11-26|2013-11-26|METHOD FOR SIMULATING WAVE PROPAGATION; SIMULATOR, COMPUTER PROGRAM AND RECORDING MEDIUM FOR IMPLEMENTING THE METHOD|FR1361645A| FR3013867B1|2013-11-26|2013-11-26|METHOD FOR SIMULATING WAVE PROPAGATION; SIMULATOR, COMPUTER PROGRAM AND RECORDING MEDIUM FOR IMPLEMENTING THE METHOD|
    US15/039,198| US10133834B2|2013-11-26|2014-11-24|Method for simulating wave propagation; simulator, computer program and recording medium for implementing the method|
    PCT/FR2014/053013| WO2015079152A1|2013-11-26|2014-11-24|Method for simulating wave propagation; simulator, computer program and recording medium for implementing the method|
    EP14815786.0A| EP3074892A1|2013-11-26|2014-11-24|Method for simulating wave propagation; simulator, computer program and recording medium for implementing the method|
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