[gdal-dev] GTiff optimisation

[Armin Burger]

On 01/09/2011 14:23, Even Rouault wrote:
>> As I did not use DATUM and PROJ creation option GDAL don't add it!
>
> Yes, the mapping between WKT representation and ECW DATUM/PROJ is not perfect,
> especially in the WKT ->  DATUM/PROJ direction (the other direction is simpler).
> You could perhaps try the updated ecw_cs.wkt file attached to ticket
> http://trac.osgeo.org/gdal/ticket/4127
>
>>
>> Finally I saw that gdal create only an aux.xml file to store his own proj
>> information and don't use the projection information from the header file. If
>> I
>> create this aux.xml file for all of my raster data it could work.
>
> Yes, .aux.xml is a solution that works for most GDAL drivers. But of course, it
> will only work in the GDAL-based software world.

I made the experience that ECW files do not work too well with the 
*.aux.xml file and less common projections. Often gdalinfo cannot 
convert the projected coordinates into lat/lon in it's output. And 
especially in combination with Mapserver reprojection does often not 
work correctly with ECW files that should read the projection info from 
the *.aux.xml file.

But as soon as you apply the ECW specific DATUM and PROJ definitions and 
add the corresponding projections/datums to the ecw_cs.wkt file (if 
missing there) everything works like a charm. Also desktop clients like 
ArcGIS 10 and QGIS work well with those ECW's if you add the missing 
projections and datums to their own copy of the ecw_cs.wkt file.

Armin