[gdal-dev] gdal_translate with -a_srs option using proj4 syntax and +a=ellipsoid

[Cassanova, Bill]

Hi all,

I have a tiff image that has been exported from meteorological software
that has know geographic parameters:

ELLIPSOID_EQUATOR_RADIUS 	6378206.5	
ELLIPSOID_POLAR_RADIUS 	6356584	
ELLIPSOID_FLATTENING 	0.00339	
UPPER_LEFT_X 	-3507992.25	
UPPER_LEFT_Y 	6780696	
LOWER_RIGHT_X 	3601343.75	
LOWER_RIGHT_Y 	2337361	
PROJECTION_TYPE 	Mercator	
CENTER_LONGITUDE_MERCATOR_SPECIFIC 	-96	
CENTER_LATITUDE 	37.910004	
CENTER_LONGITUDE 	-95.580002	
ROTATION 	0	

I am trying to convert this to a geotiff with my eventual goal of
converting it to an unprojected tiff.

First step is to add the geographic information to the tiff:

gdal_translate -a_ullr -3507992.25 6780696 3601343.75 2337361-a_srs
"+proj=merc +lon_0=96w +a=6378206.5 +f=0.00339" src_image.tiff
dest_image.tiff

The failure I get is:
Failed to process SRS definition: +proj=merc +lon_0=96w +a=6378206.5
+f=0.00339

My second attempt was the try the same above command except with a proj
string that does not include the +a or +f options
But instead "+proj=merc +lon_0=96w +datum=WGS84".  This did work.

The problem I am now having is that I bring this image into ArcInfo and
for some reason it is shifted north.  I think that being able to
correctly apply the ellipsoid equator radius and ellipsoid flattening
may fix my problem or am I missing something?

The second step is to create an un-projected image from this data:  

My presumption is the below command will accomplish
Just that:
gdalwarp -t_srs '+proj=latlong' -r ${sample_method} ${tmp_image_3}
${final_image

Any help is fully appreciated.

Thanks,
Bill



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