[Qgis-user] Reqgis 0.10 slow digitizing with grass

[Maciej Sieczka]

maning sambale pisze:
 > Maciek wrote:
 >> maning wrote:

>> I recommend exporting the "GRASS rgb images" (they are "groups",
>> are they?)

> rgb image from r.composite, using "groups" to display rasters slows 
> the render even more.

>> from GRASS into GeoTIFF with r.out.gdal.sh (if you go for the C 
>> r.out.gdal counterpart, make sure you run gdal_translate on the
>> output to reduce the file size; somehow the C r.out.gdal produces
>> GeoTIFFs bigger than gdal_translate can).

> Thanks for pointing this out.  (note to self: always run 
> gdal_translate when exporting gtiffs)

... but only when you export with the *C* version of r.out.gdal. The
*Shell script* one, r.out.gdal.sh, is itself a wrapper around
gdal_translate actually.

>> Build overviews for your GeoTIFFs with gdaladdo then (I'd go
>> external overviews - make the GeoTIFF read only and then run the
>> gdaladdo on it to achieve this). Overviews should speed up their
>> render times much.

> Right, thanks!  But, can QGIS build external overviews from native 
> GRASS rasters?

QGIS canot build external overviews at all. Which is a pitty as external
ovrs are more convenient. You need to use the gdaladdo GDAL CLI tool.

>>> a shapefile.

>> I'm not sure, but maybe building an index in QGIS can help, ?. And
>> it would not harm to process the shapefile with ogr2ogr without
>> parameters which might reduce it's size - I happened to notice this
>> works with some Shapefiles I got. At worst, even if the shapefile
>> won't render faster it will occupy less disk space and might have
>> lower memory footprint.

> I'm not editing the shapefile, but creating the index helps a bit.
> 
> I think the lag time occurs when editing, saving, re-rendering the
> GRASS vector.

Do you have "Fix problems with incorectly filled polygons" checked? It
might boost vector rendering, depending on your system, as it enables
hardware acceleration for vector rendering.

Maciek

-- 
Maciej Sieczka
www.sieczka.org