<div><font face="Arial, Helvetica, sans-serif">Hi </font><span lang="no"><font face="Arial" size="2">Sjur,<br>
<br>
Thanks for your replay. I think you are right when saying it's caused by ellipsoid. So I have used this command to reproject<br>
<br>
<i>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"<br>
<br>
</i>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. <br>
<br>
<br>
Best Regards,<br>
Jaap Knoops<br>
</font></span></div>
<div> <br>
</div>
<div> <br>
</div>
-----Original Message-----<br>
From: Kolberg Sjur A <Sjur.A.Kolberg@sintef.no><br>
To: gdal-dev@lists.maptools.org<br>
Sent: Mon, 17 Sep 2007 6:39 pm<br>
Subject: RE: [Gdal-dev] Fwd: plate carree to latlon projection problem<br>
<br>
<div id="AOLMsgPart_3_a0efd345-7c4e-4b75-98a0-65b954258b08">
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007">Jaap,</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007"></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007">Have you got your ellipsoids
right?</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007"></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007">If one of your ellipsoids (commonly the one used
with Plate-Carree) is a sphere, and you ignore that in converting to
geographical latlong (presumably based on WGS84), errors up to nearly 20 km
will occur (latitude dependent). These errors are in the N-S direction, E-W
is usually OK. This effect is beyond projection, latlong/sphere to latlong/WGS84
gives equally long offsets. Try using cs2cs and specify ellipsoids for both
input and output,</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007"></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007">It is only when one of the ellipsoids is a sphere you
get these large errors, otherwise the error is much smaller.</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007"></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007">See also Frank Warmerdam's answer on June 7th on
gdal-dev: </span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007"><em>(Re: [Gdal-dev] Does GDAL handle rotated
spheres?)</em></span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007"></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007">Best regards,</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007"></span></font> </div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007">Sjur K :-)</span></font></div>
<div dir="ltr" align="left"><font color="#0000ff" face="Arial" size="2"><span class="596452116-17092007"></span></font> </div>
<div><span lang="no"><font face="Arial" size="2">Sjur Kolberg</font></span> <br>
<span lang="no"><font face="Arial" size="2">SINTEF Energy Research</font></span> <br>
<span lang="no"><font face="Arial" size="2">N - 7465 Trondheim, Norway</font></span>
<br>
<span lang="no"><font face="Arial" size="2">Phone +47 - 73 59 72 78</font></span>
<br>
<span lang="no"><font face="Arial" size="2">Fax +47 - 73 59 72 50</font></span>
</div>
<br>
<div class="OutlookMessageHeader" dir="ltr" align="left" lang="en-us">
<hr>
<font face="Tahoma" size="2"><b>From:</b> <a href="mailto:gdal-dev-bounces@lists.maptools.org">gdal-dev-bounces@lists.maptools.org</a>
[<a href="mailto:gdal-dev-bounces@lists.maptools.org?">mailto:gdal-dev-bounces@lists.maptools.org</a>] <b>On Behalf Of
</b><a href="mailto:jjknoops@netscape.net">jjknoops@netscape.net</a><br>
<b>Sent:</b> 17. september 2007 15:37<br>
<b>To:</b>
<a href="mailto:gdal-dev@lists.maptools.org">gdal-dev@lists.maptools.org</a><br>
<b>Subject:</b> [Gdal-dev] Fwd: plate carree to
latlon projection problem<br>
</font><br>
</div>
<div></div>
Hello Everybody,<br>
<div id="AOLMsgPart_3_a2184652-c9ca-41cb-b0c4-451e8cec6560">
<div id="AOLMsgPart_3_36eb4dce-a59e-4af0-8c02-9d5e01438a37">
<div class="MsoNormal"><span><br>
I am using gdal for a couple of year now and I am
very satisfied with it. <br>
But now i have a problem with reprojecting from and
to plate carree(epsg:32662). <br>
I have data in plate carree and I need to
reproject to latlon but i there is an offset between the results and other data
that already in latlon.<br>
I have also used Erdas Imagine 9.1 to do the
reprojecting but i get a different results then from gdal. The results from
Erdas are beter then from gdal<br>
<br>
After testing it with a worldwide
dataset<font face="Arial, Helvetica, sans-serif">.</font> I found that the
offset is almost 0 at (0,0) to several km around Brittian. Is there a problem
with the reprojection using plate carree or do you use a different wgs84 then
Erdas?<br>
<br>
I am using gdal from fwtools 1.3.6<br>
<br>
Best Regards,<br>
Jaap
Knoops</span><span lang="EN-US"></span></div>
<font face="Arial, Helvetica, sans-serif"></font>
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