[Qgis-user] Re: GRASS raster reading to QGIS 1.0.0 Kore

[Patrick Giraudoux]

Martin Dobias a écrit :
> 2009/1/4 Patrick Giraudoux <patrick.giraudoux at univ-fcomte.fr>:
>   
>> Seems that I can narrow the question now. Actually, QGIS Kore reads GRASS
>> maps well except when the maps  have been created from raster ramp color
>> have been optimized with i.landsat.rgb. For example in GRASS:
>>
>> r.composite r=etm7 g=etm5 b=etm2 out=south752brut
>>
>> makes a map 'south752brut' which is well read within QGIS
>>
>> Now if I do:
>> i.landsat.rgb r=etm7 g=etm5 b=etm2
>> r.composite r=etm7 g=etm5 b=etm2 out=south752opt
>>
>> it makes a map 'south752opt' which is extremly long to read (several
>> minutes), and when read makes change (displacement, zoom, etc...) extremely
>> long to be displayed at a speed that prevent any work
>>
>> However, 'south752opt' and 'south752brut' are quick/normally displayed both
>> at the same speed when on work within GRASS (e.g. d.rast south752opt)
>>
>> Any hint ?
>>     
>
> Hi Patrick,
>
> we're using GDAL library to access GRASS rasters, so the problem may
> be there. I would suggest you to try reading the raster in some other
> GDAL-based software [1] to see whether it also suffers slow
> performance. If so, file a bug for GDAL, if the problem happens only
> in QGIS file a ticket for QGIS with details.
>
> Martin
>
> [1] https://trac.osgeo.org/gdal/wiki/SoftwareUsingGdal
>
>   
Ok. I will try and come back with the result ASAP.

Additionally before your mail I have made some other trials that may (?) 
help to understand what happens... Looks like corroborating your 
suspicion about bad interactions between rgdal and qgis. When I export 
the file using r.out.gdal format=GTiff and then try and read the tif 
file externally from QGIS, I have the same (bad/slow) result as when 
reading the grass file from QGIS within GRASS. Then, if I export the 
GRASS file with r.out.tiff I get a file which is easily read from QGIS 
and correctly (quickly) displayed as a three band tif object (as an 
external raster, of course). Furthermore, what surprises me is that when 
I read a raster GRASS file created with r.composite within QGIS, I get a 
1-grey band file  with "color palette" ("palette de couleur" in French) 
activated in the "properties" box of the layer (however, I was more 
expecting a three band rgb).

Do those info put you a bit more clearly on the track ?

Thanks for your ideas and advice to where to adress the trouble...

Patrick




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