docs:gis:projections:assigning_a_projection_to_a_raster_file [hartungdesign.net wiki]

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====== Assigning a Projection to a Raster File ======
  - gather any information about the raster file, such as the extents of the image, the projection used, etc...
  - create a [[:docs:gis:world_files|world file]] (sidecar file) for the image
  - you may now use the image with the world file if you want to input the projection every time, or you can use gdalwarp to create a new file with the projection information included

===== Tips =====
  * use the cs2cs command to convert known extend coordinates

===== Example =====
For a given raster image, we knew the limits of the latitude and longitude, and that the file was using Mercator projection
  * we were given:<code>
    Location: 15 to 60 degrees North latitude, 50 to 130 degrees West longitude
    Orientation: North toward the top, Mercator projection
    Image Data: shaded and colored SRTM elevation model
    Original Data Resolution: SRTM 1 arcsecond (about 30 meters or 98 feet)
    Date Acquired: February 2000 
</code>

  * command used to determine mercator projection data:(numbers are x y as in long lat, unless option flags are used)<code>
cs2cs +proj=latlong +ellps=WGS84 +to +proj=merc +ellps=WGS84 +lat_ts=37.5 +lon_0=-90 <<EOF
> -130 15
> -50 60
> EOF

Output:
-3537017.77     1333018.49 0.00
3537017.77      6642819.94 0.00
</code>

  * with this output and determining the resolution of the raster file at 9600 x 7240, we knew how to create an appropriate world file (coordinates are based on top left of image):<code>

scale:
(3537017.77 x 2) / 9600 = 736.8787021

world file contents:
736.8787021
0
0
-736.8787021
-3537017.77
6642819.94
</code>

  * we also knew how to adjust the projection in mapserver:<code>
...
	EXTENT -3537017.77 1333018.49 3537017.77 6642819.94
...
	PROJECTION
		"proj=merc"
		"ellps=WGS84"
		"lat_ts=37.5"
		"lon_0=-90"
	END
...
</code>