[Gdal-dev] gdal_translate Basic Usage / UTM to latlong

[Tim Osborn]

>> However, the coordinates output by gdalinfo don't look like UTM
>> coordinates....they look more like State Plane Coordinates in meters. 

>Interesting...is there a way I can confirm this?

Well, the UTM NAD83 coordinates for West 87d, 59.477 Minutes, North 43d,
48.340 Minutes, which is where you say the center of the image should be,
are 420,265.62E  4,850,766.51N 16T.  Note the magnitude of the
northing...much larger that the coordinates for the center of the image
reported by gdalinfo.  That's why the coordinate information in the image
can't be UTM.  About all that leaves is State Plane or some custom spatial
reference system.

>gdal_translate -a_srs overrides the projection for the output file. 
>There doesn't seem to be an option for defining what is on the input 
>side.  Is this because UTM is assumed assumed with gdal_translate?  Your 
>comment that the coordinates look more like State Plane Coordinates in 
>meters and that EPSG:32154 should be used as -a_srs implies that the 
>-s_srs defines both the input side and output.
>
>In an email response to by mail, someone else indicated the gdalwarp may 
>be more appropriate as both s_srs and the t_srs (source and destination) 
>coordinate systems can be overridden.  My attempts and making that work 
>were tragic.  Is this a direction I should continue to pursue?

gdal_translate -a_srs assigns a spatial reference system to an image.  If
you knew for sure what the image was projected in, and you wanted to change
it to something else, it would be appropriate to use gdalwarp.  But that's
not the problem here....we really aren't sure what the image is projected
in.  So, using gdal_translate to assign a srs is appropriate.  

It seems that there is some disjoint here.  The center of the image that you
believe is in the Wisconsin South Zone SPC, but the coordinates in the image
are such that when that Wisconsin South Zone is applied, the center of the
image is located in the Wisconsin Central Zone. I'd check back with the
source of the image and see if they can provide a prj file or more
information.
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