LUT-based system for simulating sensor-assisted perception of terrain

• US 6,735,557 B1
• Filed: 10/15/1999
• Issued: 05/11/2004
• Est. Priority Date: 10/15/1999
• Status: Expired due to Term

• Current Assignee: Aechelon Technology, Inc.
• Original Assignee: Aechelon Technology, Inc.
• Inventors: McGovern, William P., Castellar, Javier, Barcena, Luis A., Sanz-Pastor, Ignacio
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): FERRIS III, FRED O
• Application Number:
  US09/418,949
• Time in Patent Office: 1,670 Days
• Field of Search: 701/211, 703/5, 703/2
• US Class Current: 703/5
• CPC Class Codes: G06T 15/00 3D [Three Dimensional] image rendering
• CPC Class Codes: G06T 17/05 Geographic models
• CPC Class Codes: G06T 19/003 Navigation within 3D models or images
• CPC Class Codes: G06T 19/006 Mixed reality object pose determination, tracking or camera calibration for mixed reality G06T7/00

Abstract

A set of specially-configured LUT'"'"'s are used in a rasterizing portion of a graphics system for simulating Sensor-assisted Perception of Terrain (SaPOT) so that simulation of the image produced by a given sensor can proceed rapidly and with good accuracy at a per-texel level of resolution. More specifically, terrain texels-defining memory is provided with a plurality of addressable texel records where each record contains: (a) one or more material identification fields (MID'"'"'s); (b) one or more mixture fields (MIX'"'"'s) for defining mixture proportions for the materials; and (c) slope-defining data for defining a surface slope or normal of the corresponding texel. A sky-map LUT is provided for simulating the act of looking up to the sky along the normal surface vector of a given texel to thereby obtain a reading of the sky'"'"'s contribution of illumination to that terrain texel. A reflectance LUT is provided for simulating the act of reflecting filtered radiation (light) off the material surface of the given terrain texel to thereby obtain a reading of the amount of light that the surface of the texel will reflect. The reflectance and sky contribution factors are multiplied to obtain a per-texel signal representing the amount sensor-detectable light produced from each terrain texel. A generally similar approach is taken to determine what amount of sensor-detectable, black body radiation will be produced from each terrain texel. Each terrain texel is simulated as having a specifiable mixture of plural surface materials. Each terrain texel is allowed to be shadowed during different times and the per-texel shadowing is accounted for.

Claims

1. A method for providing real-time sensor simulation of a terrain, the terrain stored in a database of texture elements (texels), each texel associated with a material having an material identification (MID) and an associated normal, a plurality of the texels illuminated by at least one energy source in a sky, the method comprising:

for each MID, predetermining a sensor-modulated reflectance value for the identified material and the simulated sensor;

predetermining a first amount of radiant power originating from each of a plurality of energy sources located in a plurality of regions in the sky at a first time;

receiving a texel;

determining a region in the sky associated with the normal of the received texel;

obtaining the amount of radiant power originating from the determined region;

obtaining the predetermined sensor-modulated reflectance value of the MID associated with the received texel; and

providing a first output as a function of the obtained radiant power and the obtained sensor-modulated reflectance value.

2. The method of claim 1, further comprising:

for each MID, predetermining a sensor-modulated black body emissance at a plurality of temperatures for the identified material and the sensor;

determining a temperature of the MID associated with the received texel;

obtaining the sensor-modulated black body emissance at the determined, temperature for the identified material; and

providing as a second output the obtained sensor-modulated black body emissance.

3. The method of claim 2 wherein predetermining the sensor-modulated black body emissance at the plurality of temperatures for the identified material and the sensor further comprises:

determining a spectral sensor sensitivity for each of a plurality of wavelengths;

determining for each of the plurality of wavelengths and for each of a plurality of temperatures the black body radiation for the wavelength at the temperature; and

for each temperature, integrating the product of the determined black body radiation and the spectral sensor sensitivity over the plurality of wavelengths.

4. An The method of claim 3 further comprising storing the result of the integration in a lookup table (LUT) indexed by temperature.

5. The method of claim 2 wherein determining a temperature of the MID associated with the received texel further comprises:

predetermining an amount by which a temperature of the material associated with the MID increases as a result of solar loading;

determining an amount of solar loading received by the texel; and

obtaining the temperature increase resulting from solar loading of the texel.

6. The method of claims 5 wherein determining an amount of solar loading received by the texel further comprises:

predetermining a second amount of radiant power originating from each of the plurality of energy sources located in the plurality of regions in the sky at a second time by;

determining a spectral sensor sensitivity for each of a plurality of wavelengths;

determining for the energy source a second spectral power distribution for each of the plurality of wavelengths at the second time;

determining for the energy source an angular coverage distribution in the sky at the second time;

for each region, integrating the product of the energy source'"'"'s power distribution at the second time and its angular coverage distribution at the second time over the plurality of wavelengths to determine a second amount of radiant power for each region;

decaying the predetermined first amount of radiant power by an amount in proportion to the interval between the first and second times; and

determining as the amount of solar loading the sum of the second current radiant power and the decayed first amount of radiant power.

7. The method of claims 1, wherein predetermining a sensor-modulated reflectance value for the identified material and the sensor further comprises:

determining a spectral sensor sensitivity for each of a plurality of wavelengths;

determining a spectral reflectance for the identified material for each of the plurality of wavelengths; and

integrating the product of the spectral sensor sensitivity and the spectral reflectance over the plurality of wavelengths.

8. The method of claim 7 further comprising storing the sensor-modulated reflectance value for the identified material and the sensor in a lookup table (LUT) indexed by material identification (MID).

9. The method of claims 7 wherein the plurality of wavelengths comprise a range of wavelengths to which the sensor is responsive.

10. The method of claim 1 wherein predetermining the amount of radiant power originating from each of the plurality of energy sources located in the plurality of regions in the sky further comprises:

determining a spectral sensor sensitivity for each of a plurality of wavelengths;

determining for the energy source a spectral power distribution for each of the plurality of wavelengths;

determining for the energy source an angular coverage distribution in the sky; and

for each region, integrating the product of the energy source'"'"'s power distribution and its angular coverage distribution over the plurality of wavelengths.

11. The method of claim 10 further comprising:

storing the result of the integration in a lookup table (LUT) indexed by sky region.

12. The method of claim 11 wherein the index includes a heading and elevation.

13. The method of claim 1 wherein each texel includes associated shadowing information, the method further comprising:

responsive to the associated shadowing information of the received texel indicating that the texel is in a shadow;

providing as output an ambient value.

14. A computer program product stored on a computer readable medium for providing real-time sensor simulation of a terrain, the terrain stored in a database of texture elements (texels), each texel associated with a material having an material identification (MID) and an associated normal, a plurality of the texels illuminated by at least one energy source in a sky, the computer program product controlling a processor coupled to the medium to perform the operations of:

for each MID, predetermining a sensor-modulated reflectance value for the identified material and the simulated sensor;

predetermining a first amount of radiant power originating from each of a plurality of energy sources located in a plurality of regions in the sky at a first time;

receiving a texel;

determining a region in the sky associated with the normal of the received texel;

obtaining the amount of radiant power originating from the determined region;

obtaining the predetermined sensor-modulated reflectance value of the MID associated with the received texel; and

providing a first output as a function of the obtained radiant power and the obtained sensor-modulated reflectance value.

15. A system for performing real-time sensor simulation of a terrain, the system comprising:

a first lookup table (LUT) for providing sensor-modulated reflectance values for each of a plurality of stored material identifications (MIDs);

a second LUT for providing a radiant power value for each of a plurality of energy sources located in a plurality of regions in a sky;

a luminance generator, communicatively coupled to the first LUT and second LUT, configured to receive a texel having an associated normal, and to obtain from the first LUT a sensor-modulated reflectance value of the MID associated with the texel, and to obtain from the second LUT a radiant power value for the energy sources located in a region associated with the normal; and

an output module communicatively coupled to the luminance generator for providing as an output a function of the value obtained from the first LUT and the value obtained from the second LUT.

16. A system for providing real-time sensor simulation of a terrain, the terrain stored in a database of texture elements (texels), each texel associated with a material having an material identification (MID) and an associated normal, a plurality of the texels illuminated by at least one energy source in a sky, the system comprising:

first predetermining means, for predetermining for each MID a sensor-modulated reflectance value for the identified material and the simulated sensor;

second predetermining means, for predetermining a first amount of radiant power originating from each of a plurality of energy sources located in a plurality of regions in the sky at a first time;

receiving means, for receiving a texel;

determining means, communicatively coupled to the receiving means, a region in the sky associated with the normal of the received texel;

first obtaining means, communicatively coupled to the determining means and the second predetermining means, for obtaining the amount of radiant power originating from the determined region;

second obtaining means, communicatively coupled to the receiving means and the first predetermining means, for obtaining the predetermined sensor-modulated reflectance value of the MID associated with the received texel; and

providing means, communicatively coupled to the first obtaining means and the second obtaining means, for providing a first output as a function of the obtained radiant power and the obtained sensor-modulated reflectance value.