[gdal-dev] gdal_translate - ECW format and non-UTM projections

Armin Burger armin.burger at gmx.net
Wed Jun 8 13:36:35 EDT 2011


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<jrepetto at free.fr>
>>> An: Armin Burger<armin.burger at gmx.net>
>>> CC: gdal-dev at lists.osgeo.org
>>> 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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