[Qgis-developer] Re: Raster providers

Radim Blazek radim.blazek at gmail.com
Thu Jan 20 16:46:56 EST 2011

I have roughly implemented approximate reprojection. It should work
for GDAL and GRASS, I have not tested WMS. Currently it is always
using approximation (even if error is too big).
Rendering with reprojection takes about 5 times more.  You can get
some info about times grepping debug output, e.g.: qgis rp.qgs 2>&1 |
egrep "(time|CPMatrix size)" | sed 's/.*cpp: //'

I have got for example for reprojected raster in raster providers branch:
89: (QgsRasterProjector) CPMatrix size: mCPRows = 5 mCPCols = 9
41: (readBlock) create projector time  (ms): 10
53: (readBlock) read not projected block time  (ms): 24
71: (readBlock) reproject block time  (ms): 1022
1287: (draw) raster draw time (ms): 1446
1287: (draw) raster draw time (ms): 10

the same raster not reprojected in raster providers branch:
1287: (draw) raster draw time (ms): 323

in trunk:
1830: (draw) raster draw time (ms): 689

It is strange that it is slower in trunk.

> On Thu, Jan 13, 2011 at 7:06 PM, John C. Tull <jctull at gmail.com> wrote:
>> Comparing the load time of this raster when the project CRS is the same as the raster (i.e., no transform should be occurring), the load time still requires several minutes. This is true whether or not I have enabled on the fly reprojection in the project options. In contrast, the same file takes several seconds to load in trunk.

Are you talking about loading the raster first time or about
redrawing? Maybe statistics are not necessarily computed.


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