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

[Frank Warmerdam]

Cassanova, Bill wrote:
> ***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

Bill,

Unfortunately the OGRSpatialReference PROJ.4 parser does not support
the +f flag, but it does support +rf (inverse flattening).  Try
using +rf=294.98525 instead of the +f parameter.

If you wish, you could file an enhancement ticket requesting that
support for +f be added.

> 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

You should be specific about the target earth model by adding
something like +datum=WGS84 into the -t_srs string.

Otherwise the approach is plausible.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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