====== 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:
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
* command used to determine mercator projection data:(numbers are x y as in long lat, unless option flags are used)
cs2cs +proj=latlong +ellps=WGS84 +to +proj=merc +ellps=WGS84 +lat_ts=37.5 +lon_0=-90 < -130 15
> -50 60
> EOF
Output:
-3537017.77 1333018.49 0.00
3537017.77 6642819.94 0.00
* 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):
scale:
(3537017.77 x 2) / 9600 = 736.8787021
world file contents:
736.8787021
0
0
-736.8787021
-3537017.77
6642819.94
* we also knew how to adjust the projection in mapserver:
...
EXTENT -3537017.77 1333018.49 3537017.77 6642819.94
...
PROJECTION
"proj=merc"
"ellps=WGS84"
"lat_ts=37.5"
"lon_0=-90"
END
...