Hi Radim
thePaintDevice->logicalDpiX() = 85 thePaintDevice->logicalDpiY() = 86
sceneDpi = 96 rasterScaleFactor = 0.890625
Looks like the problem is that, in QgsRenderChecker::runTest, myImage may have
different DPI depending on the system (in your case, myImage seems to have
85/86 and myExpectedImage 96). Could you test if it works if you set the DPI of
myImage programmatically to 96:
QImage myImage( myExpectedImage.width(),
myExpectedImage.height(),
QImage::Format_RGB32 );
myImage.setDotsPerMeterX( 96.0 / 25.4 * 1000.0 );
myImage.setDotsPerMeterY( 96.0 / 25.4 * 1000.0 );
...
Like that, rasterScaleFactor
should be 1.0 on all systems.
Anybody has idea why rasterScaleFactor is used and how it should work?
rasterScaleFactor is there because in the print composer, units are mm and so
in this case, the raster images have more pixels than output units.
But for drawing to QImage, rasterScaleFactor is always 1.
Regards,
Marco
On 16.06.2012 12:53, Radim Blazek wrote:
Here it is http://dash.orfeo-toolbox.org/viewTest.php?buildid=87438
it looks interesting. In the first raster test called 'raster', some
columns are wider, some others are narrower. In following raster
tests, the problem may be the same (columns and rows somehow shifted).
More observations:
* test raster tenbytenraster.asc size is 10x10
* output device is set to expected_raster.png size 100 x 100
* QgsMapRenderer::render is using
rasterScaleFactor = ( thePaintDevice->logicalDpiX() +
thePaintDevice->logicalDpiY() ) / 2.0 / sceneDpi;
in this case:
thePaintDevice->logicalDpiX() = 85 thePaintDevice->logicalDpiY() = 86
sceneDpi = 96 rasterScaleFactor = 0.890625
* because of rasterScaleFactor, the raster is rendered as 90x90
instead of 100x100, doing such resampling, it may probably happen that
certain output column falls to a different data source column
depending on architecture - it is not clear to me however, how it
would be possible, it should be all IEEE 754, there is also IEEE
754-2008, but I have no idea if it can make difference or if it is
even implemented in new CPUs. Anyway, we should not usually reach such
problems.
Anybody has idea why rasterScaleFactor is used and how it should work?
Radim
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Dr. Marco Hugentobler
Sourcepole - Linux& Open Source Solutions
Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
[email protected] http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee
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