QGIS quickstart requires > 2G RAM

[camerons]

On 18/08/12 20:03, Micha Silver wrote:

Part of the QGIS quickstart includes showing the NVIZ (3D) module in the GRASS plugin. In a VM with < 2GB this module, with the included GRASS data throws a G_malloc error. I added a comment in the quickstart indicating that at least 2GB RAM is needed.

The Quickstart should be changed to only use examples requiring 1GB of RAM, as we note our System Requirements is at least 1 Gig RAM:

​http://live.osgeo.org/en/quickstart/osgeolive_quickstart.html

[micha]

A bit more information: The G_Malloc error does not happen in an installed VirtualBox VM, even with only 1 GB RAM. The error comes up only when running as a Live DVD system.

NVIZ is already part of the GRASS quickstart, and under GRASS it works with 1GB even in a LiveDVD system. Just to be on the safe side, it might be best to replace the NVIZ example in QGIS with some other GRASS module. Perhaps r.param.scale ? (not shown in the GRASS quickstart). THis seems to work quite well with only 1GB, both in an installed VM and a Live system (provided you set the region to the elevation@PERMANENT raster first)

[hamish]

NVIZ itself uses little RAM, it's all about how big a raster you throw at it, although in almost all circumstances 1GB should be plenty.

Please check that the quickstart mentions to set the computational region from the raster map before doing anything, otherwise it will be slow and memory consuming as it resamples the data to e.g. 1m resolution instead of e.g. 30m x 30m.

I'll have a look though.

Hamish

[hamish]

yeah, so QGIS seems to be reading in the default region of the mapset, but then altering the resolution to that of the currently opened raster map. So if you turn on the Plugins -> GRASS -> Display region red box and zoom out, you can see that the computational region is very large compared to the demo map that was opened, and it will be working on a 8166 x 7350 cell grid. Setting the region through Plugins -> GRASS -> Edit current region then drawing a box around the current raster view isn't too great either, as it doesn't match the map's region exactly causing it to have to resample to the new grid resolution, which isn't as fast as reading at the native resolution.

The solution is in the nviz startup options click on the "use region of this map" box to the right of the raster map dropdown list)

should be fixed in r9082.

thanks for noticing, Hamish

ps- the trac self-logout/timeout thing is still happening! argh