Frank, Jean-Claude,
thanks for pointing me to the ECW definitions. My main problem are
currently the missing ETRS89/GRS80 definitions for several pan-European
projections that are missing. Some national projections I need I could
already identify and I will try them. If a projection is missing can I
add it and GDAL will try to use it when reading and creating ECW files?
Regarding the datums I guess I will be limited to the ones available in
this list an understood by the ECW library, right?
Is there a way to update an ECW file adding this type of information via
GDAL API functions? I know there was a Windows GUI tool from ER Mapper
some years a go that could modify some kind of ECW header, but I would
need to run this on at least several 100's of files, so a manual
approach is not feasible. Or do I need to re-create all ECW's and add
the projection options?
I will try to put together a good description for a ticket and then I
will create one.
One funny observation I made for the mentioned case where using the ECW
file via MapServer WMS was not applying a datum shift: I made a quick
test defining the ECW as only source of a virtual image using the
standard projection definition for the VRT image. Using this VRT as
layer data source in Mapserver the datum shift was applied...
Best regards
Armin
On 08/06/2011 17:44, Frank Warmerdam wrote:
On 11-06-08 11:30 AM, Armin Burger wrote:
Jean-Claude
I guess it's not only a problem of gdalinfo but of some parts of GDAL
in general dealing with the ECW.
I made some more tests and when I add the options
-co DATUM=WGS84 -co PROJ=NUTM32
to the gdal_translate call then gdalinfo identifies the coordinates
correctly afterwards, but then of course the whole projection is set
to UTM...
It seems that the default value entered for DATUM is "RAW" and that
seems to cause some of the problems afterwards for GDAL. The problem
for me is that I need to insert the correct datum and projection using
the syntax of ECW, and I don't know if all available
datums/projections used e.g. in Europe are supported, and which syntax
to use for the available ones.
I found on my Windows installation a file "PcskeyProjDatum.dat" with a
few definitions of projection and datum used but this was very limited
and covered mainly UTM and NAD. Most European projections and datums
were missing in this file.
Armin,
GDAL skips with a file data/ecw_cs.wkt that lists many ECW
projections and datums. Perhaps it will be helpful.
There are definately problems translating coordinate system
into the ECW dictionary. A ticket for a particular case
*might* lead to some improvement but it is an iffy process.
Part of the problem in the thread mentioned by Jean-Claude
is that when the coordinate system translation fails GDAL
also gives up on read the georeferencing transform - or at
least I think it used to work this way. I think there may
have been some recent fixes in this regard. If not, a ticket
might be appropriate.
Best regards,
-------- Original-Nachricht --------
Datum: Wed, 08 Jun 2011 16:27:22 +0200
Von: Jean-Claude Repetto<[email protected]>
An: Armin Burger<[email protected]>
CC: [email protected]
Betreff: Re: [gdal-dev] gdal_translate - ECW format and non-UTM
projections
Hi,
I think there is a bug in gdalinfo, I already noticed this kind of
problem, for example
<http://osgeo-org.1803224.n2.nabble.com/gdal-dev-corner-coords-in-tif-vs-ecw-td5608144.html>
You should file a bug at<http://trac.osgeo.org/gdal/> .
Jean-Claude
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