[Qgis-developer] Approximate reprojection for vectors

[Radim Blazek]

On Sun, Oct 2, 2011 at 9:33 PM, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> > I did a lot of profiling for the
FOSS4G WMS benchmark (osm data, reprojected to
> google crs, complex symbology with a lot of rules). The pattern was mostly the
> following:
> the rendering itself (QPainter->drawPolyline) was the most time consuming
> operation (appr. 50% of rendering time),

I always thought that Qt4 rendering engine is quite efficient. Also in
my case (I am testing with Shapefile) QPainte::drawPolyline takes only
0.05% (!!!), it seems that I am looking on some wrong results comaring
to your 50%, but I cannot find what am I doing wrong.
Could it be that a different paint device is doing the difference? But
when rendering on screen, we are using QImage or QImage anyway and in
that case graphics card's power is not used, is it?

> next was evaluation in rule based
> renderer (20% of time), getNextFeature in PostgresProvider 10%, coordinate
> transformation 10%.

In my case, with Shapefile, QgsOgrProvider::getNextFeature is taking
over 50% and most of it is strcasecmp in GDAL (probably because of
unnecessary calls from QGIS (for Frank, if you are reading this)). I
believe that it can be optimised, I'll look at it.

Radim