I probably don't have the technical means to use that.
On 06/10/17 01:12, Régis Haubourg wrote:
here it is: http://www.gdal.org/gdal_vrttut.html
you can assemble raster of vector files, apply filters, reprojections,
build pyramids to avoid fetching the lowest resolution data. This is
pretty efficient.
Cheers
Régis
2017-10-05 14:10 GMT+02:00 Patrick Dunford <[email protected]
<mailto:[email protected]>>:
I don't know what this is.
On 06/10/17 01:08, Régis Haubourg wrote:
Hi Patrick ,
did you consider using GDAL VRT to avoid opening so much files?
In my experience, this works well.
Régis
2017-10-05 13:48 GMT+02:00 Patrick Dunford
<[email protected] <mailto:[email protected]>>:
Some time ago in a discussion of a particular bug a
contributor expressed concern that the refresh of background
rasters (aerial photography) in Windows was too slow.
Maybe this is the reason that recent versions of master
appear to be loading all of the background imagery into
memory (I use a master from January this year to work around
issues with later ones, and that master does not have this
feature).
Unfortunately if there are a lot of rasters then the memory
demand is excessive and unsurprisingly slows down the
computer negating any purported benefit of caching.
As an example a project I am currently working on has about
900 aerial photo images (GeoJpeg). When the layer is turned
on for display, Qgis requires about 46 GB of virtual memory.
Since my computer only has 24 GB of physical memory, it is
required to dip into the swap space considerably. Even with
60 GB of swap space on an SSD, the swapping needed to refresh
the canvas is substantial and dramatically reduces
performance resulting in substantial delays. Compare with the
January master referred to above which only requires about 7
GB of virtual memory total with the aerial photo layer
displayed. The time needed to refresh the canvas is less than
1 second, most of the time.
I know that the canvas refresh in Windows with aerial photos
can be substantially slower than in Linux. This does not
affect me, because I don't use Windows now that I have a
stable platform for running an older Linux master alongside
the most recent one. What I do know is that the memory
demands are making it difficult to evaluate the recent
masters. I need some kind of setting to turn this caching
off. With the aerial photo layer turned off, the memory usage
of the current master is about the same as the old one, and
it's much quicker to update.
_______________________________________________
QGIS-Developer mailing list
[email protected]
<mailto:[email protected]>
List info:
https://lists.osgeo.org/mailman/listinfo/qgis-developer
<https://lists.osgeo.org/mailman/listinfo/qgis-developer>
Unsubscribe:
https://lists.osgeo.org/mailman/listinfo/qgis-developer
<https://lists.osgeo.org/mailman/listinfo/qgis-developer>
_______________________________________________
QGIS-Developer mailing list
[email protected]
List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
