[Gdal-dev] Fwd: plate carree to latlon projection problem

[jjknoops at netscape.net]

 Hi Frank and Sjur,

My problem is solved. The method from frank made a good reprojection. It's even better then the erdas reprojection.
The method was: 
gdalwarp -s_srs "+proj=eqc +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +a=6378137.0 +b=6378137.0 +units=m +towgs84=0,0,0"? -t_srs "+proj=longlat +a=6378137.0 +b=6378137.0 +towgs84=0,0,0"


 


 The only strange thing is that this means data projection parameter provided by data supplier is not correct. 

Thank you both for helping me.

Best regards,
Jaap Knoops






-----Original Message-----
From: Frank Warmerdam <warmerdam at pobox.com>
To: jjknoops at netscape.net
Cc: gdal-dev at lists.maptools.org
Sent: Tue, 18 Sep 2007 3:14 pm
Subject: Re: [Gdal-dev] Fwd: plate carree to latlon  projection problem









jjknoops at netscape.net wrote:?

> Hi Sjur,?

> 
> Thanks for your replay. I think you are right when saying it's caused by 
> ellipsoid. So I have used this command to reproject?

> 
> /call gdalwarp -s_srs "+proj=eqc +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 
> +ellps=sphere +a=6378137.0 +es=0.0 +units=m" -t_srs "epsg:4326"?

> 
> /After comparing this result with previous results then I would say it's 
> worse. The offset between the result from gdalwarp and erdas has 
> increased. My college has also compared the results with envi and found 
> that it's comparable to the erdas results.?
?

Jaap,?
?

Try:?
?

gdalwarp -s_srs "+proj=eqc +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0?

?  +a=6378137.0 +b=6378137.0 +units=m +towgs84=0,0,0" \?

?  -t_srs "+a=6378137.0 +b=6378137.0 +towgs84=0,0,0" ...?
?

This attempts to do a warp from a projection on a spherical ellipsoid?

to geographic coordinates on the same ellipsoid.?
?

Note, using +a and +ellps will conflict and isn't a good idea.  And +es?

is not recognised by GDAL's proj.4 parser which is not a complete proj.4?

parser.?
?

Best regards,?

-- 
---------------------------------------+--------------------------------------?

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

light and sound - activate the windows | http://pobox.com/~warmerdam?

and watch the world go round - Rush    | President OSGeo, http://osgeo.org?
?



 


________________________________________________________________________
Check Out the new free AIM(R) Mail -- Unlimited storage and industry-leading spam and email virus protection.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/gdal-dev/attachments/20070918/71debf3d/attachment.html