Patrick Giraudoux wrote:
Martin Dobias a écrit :
2009/1/4 Patrick Giraudoux <[email protected]>:
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
Some months ago there was discussion on this list pointing to two
possible reasons for slow rendering of rasters:
http://www.mail-archive.com/[email protected]/msg00813.html
One was tiled rasters. For some reason it seemed like rasters with tiles
(created with gdal_translate -co "TILED=YES") rendered somewhat slowly.
The second problem was incorrect CRS headers in the raster. Setting the
correct projection header with gdalwarp caused tiffs to render faster.
I don't know if this is relevant to your case. (Does i.landsat.rgb set
CRS headers??) But it's worth checking.
--
Micha
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