System and method of processing digital terrain information

• US 6,600,489 B2
• Filed: 12/14/2000
• Issued: 07/29/2003
• Est. Priority Date: 12/14/2000
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Cook, Stephen R.
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): GREEN III, THOMAS R
• Application Number:
  US09/737,271
• Publication Number:
  US 20020101419A1
• Time in Patent Office: 957 Days
• Field of Search: 345/426, 345/427, 340/995
• US Class Current: 345/426
• CPC Class Codes: G06T 15/50 Lighting effects
• CPC Class Codes: G06T 15/80 Shading
• CPC Class Codes: G06T 17/05 Geographic models

Abstract

In a mapping system using a graphics application programming interface, for every digital terrain elevation data post, a normal to the terrain surface is calculated, which is then encoded in a half-polar coordinate system. The tilt and azimuth are represented as two fixed-point integers and a color table containing the illumination colors, such as gray scale colors, are given a particular azimuth and tilt combination. The two-dimensional color table array is collapsed into a single-dimensional array by concatenating (linking together) the azimuth and tilt into a single integer. The azimuth will be the most significant position. During rendering, the graphic subsystem converts the color table.

Claims

1. A method of processing digital terrain elevation data (DTED) for a digital terrain map comprising the steps of:

obtaining digital terrain elevation data posts;

calculating a normal relative to the terrain surface for each digital terrain elevation data post;

forming a color table reference number used in a color table for each digital terrain elevation data post; and

applying a single offset to each reference number in the color table for generating a correct sun-angle color when the heading angle of the digital terrain map changes.

2. A method according to claim 1, wherein the color table reference number is representative of a gray scale color.

3. A method according to claim 1, and further comprising the step of forming the color table reference number as a hexadecimal number.

4. A method according to claim 1, and further comprising the step of calculating the normal within a polar coordinate system.

5. A method according to claim 1, and further comprising the step of locating the azimuth value within the most significant position of the color table reference number.

6. A method according to claim 1, wherein the color table reference number comprises a single integer.

7. A method according to claim 1, and further comprising the step of applying a single offset to each reference number contained in the color table.

8. A method of processing digital terrain elevation data (DTED) for a digital terrain map comprising the steps of:

processing digital terrain elevation data using a graphics application programming interface (API) to create a texture image of a plurality of terrain blocks, each terrain block having a terrain elevation data post;

calculating a normal relative to the terrain surface for each digital terrain elevation data post;

forming a color table reference number used in a color table for each digital terrain elevation data post; and

applying a single offset to each reference number in the color table for generating a correct sun-angle color when the heading angle of the digital terrain map changes.

9. A method according to claim 8, wherein the color table reference number is representative of a gray scale color.

10. A method according to claim 8, and further comprising the step of forming the color table reference number as a hexadecimal number.

11. A method according to claim 8, and further comprising the step of calculating the normal within a polar coordinate system.

12. A method according to claim 8, and further comprising the step of locating the azimuth value within the most significant position of the color table reference number.

13. A method according to claim 8, and further comprising the step of applying a single offset to each reference number contained in the color table.

14. A method according to claim 8, wherein the color table reference number comprises a single integer.

15. A method of processing digital terrain elevation data (DTED) for a digital terrain map comprising the steps of:

processing digital terrain elevation data using a graphics application programming interface (API) to create a texture image of a plurality of terrain blocks, each terrain bock having a terrain elevation data post;

calculating a normal value relative to the terrain surface for each digital terrain elevation data post as two fixed point numbers corresponding respectively to a slope tilt value and slope azimuth value;

concatenating the two fixed point numbers into a color table reference number for each digital terrain elevation data post;

applying each color table reference number as part of a color index for a color table; and

applying an offset to each reference number in the color table for generating a correct sun-angle color when the heading angle of the digital terrain map changes.

16. A method according to claim 15, wherein the color table reference number is representative of a gray scale color.

17. A method according to claim 15, and further comprising the step of forming a color table reference number as a hexadecimal number.

18. A method according to claim 15, and further comprising the step of calculating the normal within a polar coordinate system.

19. A method according to claim 15, and further comprising the step of locating the azimuth value within the most significant position of the color table reference number.

20. A method according to claim 15, and further comprises the step of applying a single offset to each color table reference number.

21. A method according to claim 15, wherein the color table reference number comprises a single integer.

22. A system for processing digital terrain elevation data (DTED) for a digital terrain map comprising:

a graphics application programming interface for receiving and processing digital terrain elevation data and creating a texture image of a plurality of terrain blocks, each terrain block having a terrain elevation data post;

a processor for calculating a normal relative to the terrain surface for each digital terrain elevation data post, forming a color table reference number for each post and used as an index in a color table, and applying a single offset to each reference number in the color table for generating a correct sun-angle color when the heading angle of the digital terrain map changes.

23. A system according to claim 22, wherein said color table reference number comprises a hexadecimal value.

24. A system according to claim 22, wherein said concatenated value has a most significant position corresponding to the azimuth value.

25. A system according to claim 22, wherein said color table comprises a plurality of numbers corresponding to gray scale values.

26. A method of processing digital terrain elevation data (DTED) for a digital terrain map comprising the steps of:

obtaining digital terrain elevation data posts;

calculating a normal relative to the terrain surface for each digital terrain elevation data post within a polar coordinate system wherein the normal comprises a slope tilt value and a slope azimuth value as two fixed point numbers that are concatenated into a color table reference number;

forming a color table reference number used in a color table for each digital terrain elevation data post; and

applying an offset to each reference number in the color table for generating a correct sun-angle color when the heading angle of the digital terrain map changes.

27. A method of processing digital terrain elevation data (DTED) for a digital terrain map comprising the steps of:

processing digital terrain elevation data using a graphics application programming interface (API) to create a texture image of a plurality of terrain blocks, each terrain block having a terrain elevation data post;

calculating a normal relative to the terrain surface for each digital terrain elevation data post within a polar coordinate system wherein the normal comprises a slope tilt value and a slope azimuth value as two fixed point numbers that are concatenated into a single table reference number;

forming a color table reference number used in a color table for each digital terrain elevation data post; and

applying an offset to each reference number in the color table for generating a correct sun-angle color when the heading angle of the digital terrain map changes.

28. A system for processing digital terrain elevation data (DTED) for a digital terrain map comprising:

a graphics application programming interface for receiving and processing digital terrain elevation data and creating a texture image of a plurality of terrain blocks, each terrain block having a terrain elevation data post;

a processor for calculating a normal relative to the terrain surface for each digital terrain elevation data post, forming a color table reference number as a concatenated value obtained from a slope tilt value and a slope azimuth value for each post and used as an index in a color table, and applying a single offset to each reference number in the color table for generating a correct sun-angle color when the heading angel of digital terrain map changes.