Author was experiencing this in 1.8, it would be nice if someone (ideally the author) could test the same with nightly master (1.9).
Etienne On Thu, Aug 23, 2012 at 2:27 PM, Radim Blazek <[email protected]> wrote: > On Thu, Aug 23, 2012 at 5:57 PM, Etienne Tourigny > <[email protected]> wrote: >> On Thu, Aug 23, 2012 at 11:00 AM, Even Rouault >> <[email protected]> wrote: >>>> It would be nice to have this bultin to gdalbuildvrt (as an optin of >>>> course) - could the authors make a patch? >>> >>> For a *byte* data type, which must be the common case, why wouldn't QGIS >>> just >>> use min=0 and max=255 when statistics are not computed ? >> >> good question. >> >> Unless I am mistaken, min/max are set to 0/255 by default, unless >> QgsRasterDataProvider::bandStatistics() or >> QgsRasterLayer::bandStatistics() is called - which is probably what >> happens. > > Default contrast enhancement in current master (may be changed in > Options > Rendering > Rasters): > Single band gray: Stretch to min / max > Multiband color (byte/band): No stretch > Multiband color (>byte/band): Stretch to min / max > Limits (min/max): Cumulative count cut. > > The min/max are calculated using 250000 pixels sample, which should be > fast. It would be useful to test the VRT without stats collected with > current master. > > It would be possible to add another default contrast enhancement for > Single band gray byte, but I believe that if the whole raster can be > rendered in reasonable time, the min/max calculation must be also fast > and contrast enhancement may be important even with byte data. > > Radim > >> I don't understand what is the problem, does the VRT load slowly >> initially, or is getting statistics rather slow? >> >> On the other hand, wouldn't a simple "gdalinfo -stats file.vrt" >> achieve the same as the linked python script, but easier to run? >> >> Etienne >> >>> >>>> >>>> Regards, >>>> Etienne >>>> >>>> On Thu, Aug 23, 2012 at 7:34 AM, Micha Silver <[email protected]> wrote: >>>> > On 23/08/2012 11:33, Giovanni Manghi wrote: >>>> >> >>>> >> http://trac.osgeo.org/gdal/wiki/CatalogueForQIS >>>> > >>>> > >>>> > Magic! Many thanks, and also to Andrea Peri for posting the python code. >>>> > In windows I had to run it as: " python computestats.py -approx >>>> > <filename.vrt> " >>>> >> >>>> >> it would be very nice to have this added as tool directly in QGIS... >>>> >> >>>> >> cheers >>>> >> >>>> >> >>>> >> -- Giovanni -- >>>> >> >>>> >> >>>> >> On Thu, 2012-08-23 at 11:27 +0300, Micha Silver wrote: >>>> >>> >>>> >>> Hello all: >>>> >>> >>>> >>> I have a batch of over 100 raster tiles in ecw format. Each is 50 - >>>> >>> 100 MB in size. When I choose 20 or so files to load they appear >>>> >>> (render) very quickly - in a matter of a few seconds or less. If I >>>> >>> create a vrt of that same batch of tiles, it takes a long time to >>>> >>> first render - upwards of 15 - 30 seconds. Once the vrt is loaded >>>> >>> response is excellent (zooming, etc). But that initial delay is a bit >>>> >>> annoying. Anything I can do to improve it? (QGIS 1.8, Win 7 64 bit) >>>> >>> >>>> >>> Many thanks, >>>> >>> Micha >>>> >>> >>>> >>> -- >>>> >>> Micha Silver >>>> >>> 052-3665918 >>>> >>> _______________________________________________ >>>> >>> Qgis-user mailing list >>>> >>> [email protected] >>>> >>> http://lists.osgeo.org/mailman/listinfo/qgis-user >>>> >> >>>> >> >>>> >> >>>> >> This mail was received via Mail-SeCure System. >>>> >> >>>> >> >>>> > >>>> > >>>> > -- >>>> > Micha Silver >>>> > 052-3665918 >>>> > >>>> > _______________________________________________ >>>> > Qgis-user mailing list >>>> > [email protected] >>>> > http://lists.osgeo.org/mailman/listinfo/qgis-user >>>> _______________________________________________ >>>> Qgis-user mailing list >>>> [email protected] >>>> http://lists.osgeo.org/mailman/listinfo/qgis-user >>>> >>> >>> >> _______________________________________________ >> Qgis-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/qgis-user _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
