[gdal-dev] gdal 1.8 and ERDAS ECW Read-Write SDK problem

[Even Rouault]

Selon netcadturgay <turgay.osna at netcad.com.tr>:

> Hi Even Rouault
> I have builded both Gdal 1.8 library and Gdal 1.9 library including ERDAS
> read-write sdk. Results:
>
> Gdal 1.9
> -------
> ReadOnly    -> OK
> Update       -> OK
(update capabilities are restricted to header information, not imagery)
> CreateCopy -> OK
> Create       -> NOT OK
>
> Gdal 1.8
> --------
> ReadOnly    -> OK
> Update       -> NOT OK
> CreateCopy -> OK
> Create       ->  NOT OK
>
> I can use gdal 1.9 but can I create .ecw files?  Or is there any creation
> method for ecw files in Gdal 1.9?

See http://www.gdal.org/classGDALDriver.html#adb7bff9007fa5190d6cf742cf76942a8
and http://www.gdal.org/classGDALDriver.html#a2c897da2a6e25169cccc49ef48797ce1
for the difference of semantics between Create and CreateCopy.

Basically CreateCopy is to convert an existing source file into the target
format, whereas Create is to create a new file that is initially empty, and then
you add georeferencing, metadata, and imagery in it, in potentially total random
order. The later is supported by very few drivers, most of the time because the
features of the file format need to write the things in a precise order due to
compression, etc....
For example, when you use gdal_translate, you just need CreateCopy()
capabilities. So yes, you can create ECW files.
This is also explained with different works in the "Techniques for Creating
Files" section and below of http://www.gdal.org/gdal_tutorial.html