Method for efficiently transforming a raster image from one map projection to another map projection

• US 7,791,616 B2
• Filed: 02/09/2007
• Issued: 09/07/2010
• Est. Priority Date: 02/10/2006
• Status: Active Grant

• Current Assignee: Navy The USA As Represented By The Secretary of The
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Ioup, Elias Z K, Mesick, Hillary C, Sample, John T
• Primary Examiner(s): Tung; Kee M
• Assistant Examiner(s): AMIN, JWALANT B
• Application Number:
  US11/673,363
• Publication Number:
  US 20070188516A1
• Time in Patent Office: 1,306 Days
• Field of Search: None
• 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:

a processor precomputing UTM coordinates for a subset of the total number of pixels in a Geodetic projection image, the subset having fewer pixels than the total number of pixels in the Geodetic projection image;

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

testing the accuracy of linear interpolation with the initially set size of the subset by, for at least one of the remaining pixels in the Geodetic projection determining an error by comparing the UTM coordinates found by the linear interpolation to directly calculated UTM coordinates for the same pixel and increasing the size of the subset if the error exceeds a predetermined value; and

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

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

assigning a color to a pixel in the Geodetic image based on the color of at least one pixel in the UTM raster image.

3. The method according to claim 2, wherein assigning a color to a pixel in the Geodetic image includes using bilinear interpolation with color values of four closest UTM pixels.

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

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

6. 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.

7. A method for reprojecting a raster image in a UTM projection into a Geodetic projection, wherein the UTM map a processor for projection image is a USGS digital orthoquad image and has fiducial markers, the method comprising:

a processor precomputing UTM coordinates for a subset of the total number of pixels in a Geodetic projection image, the subset having fewer pixels than the total number of pixels in the Geodetic projection image;

subsequently, for remaining pixels in the Geodetic projection image, finding the UTM coordinates of each pixel by linear interpolation using the precomputed UTM coordinates of the nearest surrounding precomputed pixels; and

cropping the UTM image to the area within the fiducial markers before said precomputing UTM coordinates for a subset of the total number of pixels in the Geodetic projection image.

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

generating the empty Geodetic image by converting each of the four pixels at the fiducial markers 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 fiducial markers.

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

a processor precomputing coordinates in the first map projection for a subset of the total number of pixels in an empty second map projection image, wherein the subset has fewer pixels than the total number of pixels in the empty second map projection image;

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

testing the accuracy of linear interpolation with the initially set size of the subset by, for at least one of the remaining pixels in the second map projection determining an error by comparing the first map projection coordinates found by the linear interpolation to directly calculated first map projection coordinates for the same pixel and increasing the size of the subset if the error exceeds a predetermined value; and

subsequently, the 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.

11. The method according to claim 10, 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.

12. The method according to claim 10, 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.

13. The method according to claim 10, wherein the raster image in the first map projection is a photograph.

14. The method according to claim 10, wherein the raster image in the first map projection is a photograph of a portion of the Earth.

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

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

16. A non-transitory computer readable medium storing computer readable instructions thereon for execution by a processor for converting an image from a first map projection to a second map projection image, the instructions comprising:

instructions for precomputing coordinates in the first map projection for a subset of the total number of pixels in an empty second map projection image, the subset having fewer pixels than the total number of pixels in the empty second map projection image;

instructions for setting an initial size of the subset of pixels to be precomputed;

instructions for testing the accuracy of linear interpolation with the initially set size of the subset by, for at least one of the remaining pixels in the second map projection determining an error by comparing the first map projection coordinates found by the linear interpolation to directly calculated first map projection coordinates for the same pixel and increasing the size of the subset if the error exceeds a predetermined value; and

instructions for 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.

17. The computer readable medium of claim 16, the instructions 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.

18. The computer readable medium of claim 16, 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.

19. The computer readable medium of claim 16, wherein the first map projection image is a photograph.

20. The computer readable medium of claim 16, wherein the first map projection image is a digital orthoquad photograph.

21. A non-transitory computer readable medium storing computer readable instructions thereon for execution by a processor for converting an image from a first map projection to a second map projection image, the instructions comprising:

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

instructions for 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,

wherein the first map projection image is a USGS digital orthoquad and has fiducial markers, and the instructions for cropping the first map projection image to the area within the fiducial markers before said precomputing coordinates in the first map projection for a subset of the total number of pixels in an empty second map projection image.

22. The computer readable medium of claim 21, wherein the instruction are further adapted to generate the empty second map projection image by converting each of the four pixels at the fiducial markers to second map projection coordinates.

23. The computer readable medium of claim 22, wherein the instructions are 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 fiducial markers.