[Gdal-dev] Fwd: plate carree to latlon projection problem
jjknoops at netscape.net
jjknoops at netscape.net
Tue Sep 18 05:17:46 EDT 2007
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.
Best Regards,
Jaap Knoops
-----Original Message-----
From: Kolberg Sjur A <Sjur.A.Kolberg at sintef.no>
To: gdal-dev at lists.maptools.org
Sent: Mon, 17 Sep 2007 6:39 pm
Subject: RE: [Gdal-dev] Fwd: plate carree to latlon projection problem
Jaap,
?
Have you?got your ellipsoids
right?
?
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,
?
It is only when one of the ellipsoids is a sphere you
get these large errors, otherwise the error is much smaller.
?
See also Frank Warmerdam's answer on June 7th on
gdal-dev:
(Re: [Gdal-dev] Does GDAL handle rotated
spheres?)
?
Best regards,
?
Sjur K :-)
?
Sjur Kolberg
SINTEF Energy Research
N - 7465 Trondheim, Norway
Phone +47 - 73 59 72 78
Fax +47 - 73 59 72 50
From: gdal-dev-bounces at lists.maptools.org
[mailto:gdal-dev-bounces at lists.maptools.org] On Behalf Of
jjknoops at netscape.net
Sent: 17. september 2007 15:37
To:
gdal-dev at lists.maptools.org
Subject: [Gdal-dev] Fwd: plate carree to
latlon projection problem
Hello Everybody,
I am using gdal for a couple of year now and I am
very satisfied with it.
But now i have a problem with reprojecting from and
to plate carree(epsg:32662).
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.
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
After testing it with a worldwide
dataset. 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?
I am using gdal from fwtools 1.3.6
Best Regards,
Jaap
Knoops
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