[Qgis-user] Raster data formats

[Tim Sutton]

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Hi

Alex Mandel wrote:
> Juan Pedro Pérez Alcántara wrote:
>> Hello,
>>
>> perhaps this is a silly one, but I'm quite frustrated with conversions
>> from popular raster formats in the Windows/ArcGIS world to the
>> Linux/QGIS one. For example, ECW and MrSID are most popular. I think
>> JPEG2000 should be a good candidate for a raster format in QGIS. As far
>> as I know, it is fast (piramidized by nature, so to say),
>> georreferenced, and they work flawlessly and smoothly (my experience, at
>> least) in QGIS. Perhaps all of you, much experienced than me for sure,
>> think that JPEG2000 is not the way and that GeoTIFF or whatever should
>> do the job. If it is so, I'll stick obviously to that option instead.
>>
>> I have been messing around with quite a bunch of libraries to deal with
>> the conversion. First, there is GDAL, with which I'm able to transform
>> ECW to almost any GeoTIFF or JPEG that works with QGIS very well, and
>> with JPEG compression, not so far in size from the ECW source. But then
>> I tried to use ImageMagick and/or Jasper to convert to JPEG2000, and
>> here is where I get stuck. I stripped off in gdal_translate the GeoTIFF
>> tags with BASELINE, but to no avail in ImageMagick, it says always (with
>> TIFF, JPEG, etc.) that it cannot write the image. Same with JASPER: I
>> tried to convert from a gdal_translated jpeg, but without result. What
>> is that I'm missing? Do you have a proven workflow to do this job? 
>>
>> And with MrSID... not experimented by now, but I tremble only thinking
>> in that :)
>>
>> Perhaps I'm too obsessed with size (file sizes, I mean!!! :) ), and I'm
>> messing around too much with that subject, when GeoTIFF is providing
>> good results with a slight size increase. Given the size of hard drives
>> today (and that I'm not in the massive storage business in the GIS
>> scene), I think is a fair trade-off for an easy and straightforward
>> conversion workflow. I'd like very much to hear your opinions about
>> this.
>>
>> Thanks in advance, this is my first post. QGIS is great and thanks to it
>> and we have almost left behind the so-called industrial standard in GIS.
>> Congratulations for the great job.
>>
>> Greetings from Spain,
>>
>> Juan Pedro Pérez Alcántara
>>
> 
> I think I'm a little confused, if you have GDAL compiled with ECW and
> MrSID format these should open in QGIS. Note the most recent version of
> the windows QGIS standalone is shipping with MrSID support.
> 
> FYI, the MrSID license is more open, and LizardTech is a sponsor of OSGEO.
> 
> Alex

Also note that if you want ECW support in windows builds of QGIS 1.0.2
or 1.1.0, you can simply download the ECW dlls from Erdas (by getting
the SDK) and place the dlls into the Quantum GIS/bin directory. We could
not include them in the installer by default for licensing reasons, but
by adding those dlls its pretty easy to get it working.

Also note that in my testing the JASPER jp2 raster loading via GDAL is
quite slow (frustratingly slow really) on the only real performant way
to use a wavelet compressed raster at this stage is to use the Kakadu,
Mr Sid or ECW drivers (all of which are proprietary software).

Lastly it is probably more appropriate to use gdal_translate to convert
between raster formats than imagemagick, since gdal's conversions are
'spatially aware' and will retain all georeferencing etc. data in the image.

Regards


- --

Tim Sutton - QGIS Project Steering Committee Member (Release  Manager)
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