METHOD AND DEVICE FOR SIMULATING THE VISIBILITY OF A PAINT FOR A LIDAR SENSOR, WHICH PAINT IS APPLIED TO A SURFACE

Abstract

Described herein is a method for simulating a visibility of a coating applied on a surface for a LiDAR sensor, which includes at least the following steps: applying the coating on the surface (301); measuring a respective reflection of light having an operating wavelength of the LiDAR sensor from the surface coated with the coating at a multiplicity of illumination and/or measurement angles (302); adapting a bidirectional reflectance distribution function for the coating as a function of the respective illumination and/or measurement angle to the respective measured reflections (303); simulating a propagation of the light emitted by the LiDAR sensor and reflected by the surface coated with the coating on the basis of the adapted bidirectional reflectance distribution function by means of a ray tracing application (304); outputting a brightness image.

Claims

1. A method for simulating a visibility of a coating applied on a surface for a LiDAR sensor, which comprises at least the following steps: applying the coating on the surface (301); measuring a respective reflection of light having an operating wavelength of the LiDAR sensor from the surface coated with the coating at a multiplicity of illumination and/or measurement angles (302); adapting a bidirectional reflectance distribution function for the coating as a function of the respective illumination and/or measurement angle to the respective measured reflections (303); simulating a propagation of the light emitted by the LiDAR sensor and reflected by the surface coated with the coating on the basis of the adapted bidirectional reflectance distribution function by means of a ray tracing application (304), the LiDAR sensor being simulated as a unit comprising a point light source (101) and a camera (102), and the surface coated with the coating being simulated as a profile (103, 202) which is arranged at a variable distance with a variable orientation in front of the camera (102); and outputting a brightness image (201), which shows a brightness of the light reflected by the profile (103, 202) in the direction of the LiDAR sensor while taking into account the adapted bidirectional reflectance distribution function (305).

2. The method as claimed in claim 1, wherein how much light is reflected by different regions of the profile (103, 202) simulating the surface is determined by means of the brightness image (201) which has been output.

3. The method as claimed in claim 1, wherein the brightness threshold value, which is defined by a reflected brightness of a reference template with a diffuse reflection of 10%, is applied to the brightness image (201).

4. The method as claimed in claim 1, wherein a visible region of the profile (103, 202) simulating the surface is quantified as a fraction of a maximum visible region of the profile (103, 202) simulating the surface for a current orientation or setting of the profile (103, 202) relative to the simulated LiDAR sensor.

5. The method as claimed in claim 1, wherein the bidirectional reflectance distribution function for the coating is formed from a weighted diffuse Lambert term and a Cook-Torrance illumination model term having at least one specular lobe.

6. The method as claimed in claim 1, wherein parameters of the bidirectional reflectance distribution function are optimized with respect to a cost function during the adaptation of the bidirectional reflectance distribution function for the coating.

7. The method as claimed in claim 6, wherein the cost function is formed on the basis of a penalty term and a sum of squared differences between the measured respective reflections and respective reflections simulated on the basis of the bidirectional reflectance distribution function.

8. The method as claimed in claim 6, wherein the parameters of the bidirectional reflectance distribution function are optimized with a nonlinear optimization method.

9. The method as claimed in claim 1, wherein the profile (103, 202) simulating the surface is selected as a vehicle contour.

10. The method as claimed in claim 1, which is carried out for a multiplicity of coating formulations, wherein the output respective brightness images (201) for the different coating formulations are compared with one another and that coating formulation which is most highly visible for the LiDAR sensor is selected from the multiplicity of coating formulations.

11. A device for simulating a visibility of a coating applied on a surface for a LiDAR sensor, which comprises at least: an application unit for applying the coating on the surface; a measuring arrangement for measuring a respective reflection of light having an operating wavelength of the LiDAR sensor from the surface coated with the coating at a multiplicity of illumination and/or measurement angles; a computer unit for adapting a bidirectional reflectance distribution function for the coating as a function of the respective illumination and/or measurement angle to the respective measured reflections; a simulation unit for simulating a propagation of the light emitted by the LiDAR sensor and reflected by the surface coated with the coating on the basis of the adapted bidirectional reflectance distribution function by means of a ray tracing application, the LiDAR sensor being simulated as a unit comprising a point light source (101) and a camera (102), and the surface coated with the coating being simulated as a profile (103, 202) which is arranged at a variable distance with a variable orientation in front of the camera; and an output unit for outputting a brightness image (201), which shows a brightness of the light reflected by the profile (103, 202) in the direction of the LiDAR sensor while taking into account the adapted bidirectional reflectance distribution function.

12. The device as claimed in claim 11, wherein the measuring unit comprises at least one goniospectrometer.

13. The device as claimed in claim 11, which is configured for carrying out a method for simulating a visibility of a coating applied on a surface for a LiDAR sensor, which comprises at least the following steps: applying the coating on the surface (301); measuring a respective reflection of light having an operating wavelength of the LiDAR sensor from the surface coated with the coating at a multiplicity of illumination and/or measurement angles (302); adapting a bidirectional reflectance distribution function for the coating as a function of the respective illumination and/or measurement angle to the respective measured reflections (303); simulating a propagation of the light emitted by the LiDAR sensor and reflected by the surface coated with the coating on the basis of the adapted bidirectional reflectance distribution function by means of a ray tracing application (304), the LiDAR sensor being simulated as a unit comprising a point light source (101) and a camera (102), and the surface coated with the coating being simulated as a profile (103, 202) which is arranged at a variable distance with a variable orientation in front of the camera (102); and outputting a brightness image (201), which shows a brightness of the light reflected by the profile (103, 202) in the direction of the LiDAR sensor while taking into account the adapted bidirectional reflectance distribution function (305).

14. A computer program product comprising a computer program, having program code means which are configured in order to carry out at least the computer-assisted steps of the method as claimed in claim 1 when the computer program is run on a computer unit.

15. The method as claimed in claim 6, wherein the parameters of the bidirectional reflectance distribution function are optimized with the Nelder-Mead downhill simplex method.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0093] FIG. 1 shows a structure of a possible virtual measuring arrangement such as is the basis, in one embodiment of the method according to the invention, of the simulation to be carried out in this case.

[0094] FIG. 2 shows an example of a brightness image such as is output when carrying out another embodiment of the method according to the invention.

[0095] FIG. 3 shows a flowchart of one embodiment of the method according to the invention.

[0096] FIG. 1 shows a structure of a measuring arrangement 100 such as may be the basis, in one embodiment of the method according to the invention, of the step of simulating a propagation of the light emitted by the LiDAR sensor and reflected by the surface coated with the coating. A point light source 101, which emits light uniformly in all directions, is shown. Furthermore shown is a camera 102, which is arranged at or at least in the vicinity of the point light source 101. The point light source 101 emits laser beams 104, in general laser pulses, with a wavelength of 905 nm or 1550 nm, in the direction of a profile 103, which is in this case configured as a vehicle contour and simulates the surface coated with the coating. The light beams 105, or laser pulses, striking the vehicle contour 103 are at least partially reflected by the vehicle contour 103 and are sent back as reflected light beams 105, or laser pulses, in the direction of the camera 102. The camera 102 records the reflected light beams 105. The distance of the vehicle contour 103 from the camera 102 may in this case be varied during the simulation. The same applies for the orientation of the vehicle contour 103 relative to the camera 102. From the reflections, or reflection values, recorded in the simulation by the camera 102, a brightness image can ultimately be calculated and represented on a display unit (not shown here), as shown for example in FIG. 2.

[0097] FIG. 2 shows, in FIG. 2a, a brightness image 201 such as may be represented on a display unit as a result of the simulation method which has been carried out. The brightness of respective regions of the profile 202 is rendered, or represented, by a respective patterning/shading of the respective regions, a patterning/shading respectively being assigned to a scale value, or scale range, on a scale 203 of brightness values in the range of from 0.0 to 1.0 (a.u. in this case stands for arbitrary unit, in order to indicate a relative quantity). The respective patterning/shading may also be replaced with respective colors, in which case the scale 203 is to be selected as a corresponding color scale. In this case, the colors may for example range from dark blue for a scale value of 0.0 through green in the region of 0.5 to red at a scale value of 1.0.

[0098] FIG. 2b shows an image 204 of a visibility of the same profile 202 as shown in FIG. 2a. It can be seen in

[0099] FIG. 2b that, on the basis of the brightness, an assessment is to be made concerning which parts of the profile 202, or of the vehicle contour, are highly visible and which are substantially invisible, and consequently increase a possible risk of collision of the vehicle comprising the LiDAR sensor with another vehicle during use in autonomous driving. Such an image of the visibility is derived from the brightness image and may be represented in addition or as an alternative to the brightness image on a display unit or output unit provided according to the invention.

[0100] FIG. 3 shows in a schematic representation a flowchart of a sequence of one possible embodiment of the method according to the invention. In a step 301, a coating having a particular coating formulation is initially applied on a surface, preferably a sample surface in the form of a small flat face. The surface coated in this way with the coating is measured in a step 302, for example with the aid of a gonio-spectrophotometer, with respect to its reflection properties. This means that the surface is illuminated with light having an operating wavelength of a LiDAR sensor, and the light reflected by the surface coated with the coating is recorded by the gonio-spectrophotometer and evaluated. In this case, the surface is measured at a multiplicity of illumination and/or measurement angles. This means that the illumination unit, or a light beam coming from the illumination unit, preferably a laser pulse, having an operating wavelength of the LiDAR sensor is directed successively at a multiplicity of illumination angles onto the surface coated with the coating. Furthermore, the respectively reflected light beams, or the reflected laser beam or pulse, is recorded with the gonio-spectrophotometer, and its light quantity and/or intensity is determined. It is additionally conceivable to orientate the gonio-spectrophotometer successively at different measurement angles relative to the surface coated with the coating. It is conceivable to keep the illumination angle fixed and to vary the measurement angle, or conversely to vary the illumination angle and keep the measurement angle fixed.

[0101] It is also conceivable to illuminate the surface with white light which also comprises the operating wavelength of the LiDAR sensor. With the aid of the gonio-spectrometer, the intensity of the light that is reflected at the operating wavelength of the LiDAR sensor, is then measured.

[0102] During the measurement of a respective reflection of the light striking the surface coated with the coating, respective reflection values are correspondingly determined. With the aid of the reflection values, respective brightness values can in turn be determined. Accordingly, after the measurement, respective reflections or respective reflection values, and in association therewith respective brightness values, are available for respective illumination and/or measurement angles.

[0103] In a step 303, the respective measured reflections are used in order to adapt a bidirectional reflectance distribution function for the coating, with which the surface is coated, as a function of the respective illumination and/or measurement angles. This means that the parameters of the bidirectional reflectance distribution function for the coating are determined, or at least estimated, with the aid of the measured reflections or reflection values. The respective measured reflections yield a multiplicity of equations, having still unknown parameters that with a sufficient number of measured reflections, can be determined or at least estimated. A specific bidirectional reflectance distribution function with fixed parameters, which is to be indicated, is therefore obtained for the coating, with the aid of which a respective reflection can be indicated as a function of a respective illumination and/or measurement angle.

[0104] On the basis of the now adapted bidirectional reflectance distribution function, it is now possible, in a step 304, to simulate a propagation of the light emitted by the LiDAR sensor and reflected by the surface coated with the coating by means of a ray tracing application. The LiDAR sensor is in this case simulated, or modeled, as a point light source which emits light of a particular wavelength, namely an operating wavelength of the LiDAR sensor, for example 905 nm or 1550 nm, uniformly in all directions. The modeled LiDAR sensor furthermore comprises a camera which is configured in order to record light beams and determine their light quantity and/or light intensity. The surface coated with the coating is modeled during the simulation as a profile which is arranged at a variable distance with a variable orientation in front of the camera. This means that, during a respective simulation of a propagation of the light emitted by the LiDAR sensor and reflected by the surface coated with the coating, the profile may be simulated as respectively arranged in front of the camera at a different distance and/or with a different orientation. By using the adapted bidirectional reflectance distribution function, a computer graphics model is applied to the profile.

[0105] On the basis of the propagation simulated in this way, of the light emitted by the LiDAR sensor and reflected by the surface coated with the coating, in a step 305 it is now possible to output, or display on a display unit, a brightness image which shows a brightness (luminance) of the light reflected by the profile in the direction of the LiDAR sensor while taking into account the adapted bidirectional reflectance distribution function. In this case, the brightness image may explicitly be displayed as light on a display unit, or respective values of the brightness may be indicated for the coating and assigned thereto. In general, the described method is carried out for a multiplicity of different coatings and associated coating formulations, so that ultimately a comparison may be carried out between the coatings with the aid of the respective brightness images, and that coating, or the associated coating formulation, may be selected whose brightness image implies that the coating is most highly visible for a LiDAR sensor and therefore an object coated with the coating is most highly detectable for a LiDAR sensor.