[Gdal-dev] Fixing projections with GDAL_TRANSLATE vs. GDALWARP

[Matt Wilkie]

Hi Rich,

  > Yet it's odd that the very same specification of coordinate system, if
> given to gdal_warp via the -s_crs argument, works correctly.   It's
> almost like the -s_crs argument works but -t_crs is not working, or
> else the Merc_1 info is being interpreted correctly when specified on
> the command linke, but written incorrectly written to or read from a
> GeoTIFF file.

To my understanding identical *_srs arguments should have identical 
results across  all of the gdal utilities. I tested this with your data 
and without applying a spatial transform and the output is identical to 
gdal_translate using -a_srs, save that some TIFFTAG metadata is stripped.

--- windows .bat ----
@echo off
:: warp vs trans
set inProj="+proj=merc +lat_ts=41.65 +lon_0=-70.3166667 +datum=nad83"

gdalwarp -s_srs %inProj% -t_srs %inProj% mb_backpc30m.tif merc-warp.tif
gdal_translate -a_srs %inProj% mb_backpc30m.tif merc-trans.tif
--------------------


>> This bug is filed as http://trac.osgeo.org/gdal/ticket/1471 - gdalwarp
>> should keep georeferencing info
> 
> According to my reasoning, I think this is not a problem of gdalwarp
> not keeping the georeferencing info.   It could be a problem of not
> being able to correctly read/write merc 1_sp info into the geotiff
> correctly.

Hmm, yes, I guess that might be where the problem lies. I've been up and 
down this so many times I don't know where I am anymore! Time to leave 
it for now. :)


> P.S. Should this type of discussion take place here, or in trac ticket comments?

I don't really know. My inclination is to have discussion on the list 
and distilled results to the ticket. It's the developers who use the 
tickets the most, so I think they would have to weigh in to know which 
is actually the most useful in practice.

cheers,

-- 
matt wilkie
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