[Qgis-developer] Rotated and Upsidedown Rasters

[Frank Warmerdam]

Folks,

QGIS appears not to support rotated or upside down rasters very well.
I have filed bug:

   https://svn.qgis.org/trac/ticket/813

on this issue.  For my case, an upside raster, it did not show up at
all.  I have made changes in the raster-transparency branch (which I gather
will go into QGIS 1.0) such that rotated, shared and upsidedown rasters will
be displayed, and in the correct bounding box on the map, but with the
wrong orientation.  For instance, in the case of my upsidedown image it is
shown in the right area, but flipped.  The georeferencing for points is
thus quite wrong (well except in the center of course).

I see this as an expedient to let people see their data, but only a stop
gap to eventual implementation of properly displayed rotated rasters.  But
to do that we would need a more general sort of resampling operation between
the file and the display.  That's more than I'm willing to address now.
Possibly, with help from Pete, this might be something that could be
considered for 1.0.

Actually, as I think about it, another alternative used by some other
software packages (ie. Cadcorp SIS) is to create a GDAL "warped VRT"
in memory that will take care of resampling on the fly within GDAL.

That's quite an interesting angle.  I think I'll pursue that angle!

In the meantime, a heads up on a change of behavior and an intent to
address the problem more generally.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org