Method for Efficiently Transforming a raster image from one map projection to another map projection

• US 20070188516A1
• Filed: 02/09/2007
• Published: 08/16/2007
• Est. Priority Date: 02/10/2006
• Status: Active Grant

• Current Assignee: Navy The USA As Represented By The Secretary of The
• Original Assignee: Navy The USA As Represented By The Secretary of The
• Inventors: Mesick, Hillary, Sample, John, Ioup, Elias
• Granted Patent: US 7,791,616 B2
• Time in Patent Office: Days
• US Class Current: 345/606
• CPC Class Codes: G06T 3/00 Geometric image transformations in the plane of the image

Abstract

A method and system for efficiently converting an image from a first map projection to a second map projection image. The method includes precomputing coordinates in the first map projection for a subset of the total number of pixels in an empty second map projection image and subsequently, finding the first map projection coordinates of each of the remaining pixels by linear interpolation using the precomputed first map projection coordinates of the nearest surrounding precomputed pixels. A color is assigned to the second map projection image pixel with bilinear interpolation using color values of surrounding first map projection pixels. If the first map projection has fiducials, only the area within the fiducials is considered. An embodiment converts a USGS DOQ in UTM format into Geodetic coordinates.

Claims

1. A method for reprojecting a raster image in a UTM projection into a Geodetic projection, the method comprising:

precomputing UTM coordinates for a subset of the total number of pixels in a Geodetic image; and

subsequently,

for remaining pixels in the Geodetic projection image, finding the UTM coordinates of a pixel by linear interpolation using the precomputed UTM coordinates of the nearest surrounding precomputed pixels.

2. The method according to claim 1, further comprising:

setting an initial size of the subset of pixels to be computed;

testing the accuracy of linear interpolation with the initial size; and

increasing the size of the subset if necessary.

3. The method according to claim 1, assigning a color to a pixel in the Geodetic image based on the color of at least one pixel in the UTM raster image.

4. The method according to claim 1, wherein assigning a color to a pixel in the Geodetic image includes using bilinear interpolation with color values of four closest UTM pixels.

5. The method according to claim 1, wherein the raster image in the UTM projection is a U.S. Geological Survey digital orthoquad photograph.

6. The method according to claim 1, wherein the raster image in the UTM projection is a photograph of a portion of the Earth.

7. The method according to claim 1, wherein the UTM map projection image has fiducials, the method also includes:

cropping the UTM image to the area within the fiducials.

8. The method according to claim 7, further comprising:

generating the empty Geodetic image by converting each of the four pixels at the fiducial points to Geodetic coordinates.

9. The method according to claim 8, further comprising:

defining the corners of the empty Geodetic image as the Geodetic coordinates of a minimum bounding box around the Geodetic coordinates of the fiducials.

10. The method according to claim 1, further comprising:

outputting the Geodetic image to a printer, saving the Geodetic image as a file to a storage device, or outputting the Geodetic image to another program or device for further processing.

11. A method for reprojecting a raster image in a first map projection into a second map projection, the method comprising:

precomputing coordinates in the first map projection for a subset of the total number of pixels in an empty second map projection image; and

subsequently,

for each of the remaining pixels in the empty second projection image, finding the first map projection coordinates of that pixel by linear interpolation using the precomputed first map projection coordinates of the nearest surrounding precomputed pixels.

12. The method according to claim 11, further comprising:

setting an initial size of the subset of pixels to be computed;

testing the accuracy of linear interpolation with the initial size; and

increasing the size of the subset if necessary.

13. The method according to claim 11, further comprising:

assigning a color to a pixel in the second map projection image based on the color of at least one pixel in the first map projection image.

14. The method according to claim 11, wherein assigning a color to a pixel in the second map projection image includes using bilinear interpolation with color values of four closest first map projection pixels.

15. The method according to claim 11, wherein the raster image in the first map projection is a photograph.

16. The method according to claim 11, wherein the raster image in the first map projection is a photograph of a portion of the Earth.

17. The method according to claim 11, wherein the first map projection image has fiducials, the method also includes:

cropping the first map projection image to the area within the fiducials.

18. The method according to claim 17, further comprising:

generating the empty second map projection image by converting each of the four pixels at the fiducial points to second map projection coordinates.

19. The method according to claim 18, further comprising:

defining the corners of the empty second map projection image as the second map projection coordinates of a minimum bounding box around the second map projection coordinates of the fiducials.

20. The method according to claim 11, further comprising:

outputting the second map projection image to a printer, saving the second map projection image as a file to a storage device, outputting the second map projection image to another program or device for further processing.

21. A software program for converting an image from a first map projection to a second map projection image, the software configured to:

precompute coordinates in the first map projection for a subset of the total number of pixels in an empty second map projection image; and

subsequently,

for each of the remaining pixels in the empty second projection image, find the first map projection coordinates of that pixel by linear interpolation using the precomputed first map projection coordinates of the nearest surrounding precomputed pixels.

22. The software program of claim 21, further configured to:

set an initial size of the subset of pixels to be computed;

test the accuracy of linear interpolation with the initial size; and

increase the size of the subset if necessary to achieve a desired accuracy.

23. The software program of claim 21, further configured to:

assign a color to a pixel in the second map projection image based on the color of at least one pixel in the first map projection image.

24. The software program of claim 21, wherein assigning a color to a pixel in the second map projection image includes using bilinear interpolation with color values of four closest first map projection pixels.

25. The software program of claim 21, wherein the first map projection image is a photograph.

26. The software program of claim 21, wherein the first map projection image is a digital orthoquad photograph.

27. The software according to claim 21, wherein the first map projection image has fiducials, and the software is further adapted to crop the first map projection image to the area within the fiducials.

28. The software according to claim 27, wherein the software is further adapted to generate the empty second map projection image by converting each of the four pixels at the fiducial points to second map projection coordinates.

29. The software according to claim 28, wherein the software is further adapted to define the corners of the empty second map projection image as the second map projection coordinates of a minimum bounding box around the second map projection coordinates of the fiducials.

30. The software according to claim 21, wherein the software is compiled on a computer.

31. The software according to claim 21, wherein the software is not compiled.

32. The software according to claim 21, wherein the software is in C language.