[GRASS-user] volume query (in Qgis, grass 6.4.3 and grass 7)

[Vinnie Mitha]

Hi mailing list

I have a query re: Grass with which I hope you are able to assist (v.6.4.3 as standard installation with Qgis 2.2.20 Valmiera).

I would like to calculate volume from an upper and lower DEM (surfaces) but this is not working.
I have used both the Qgis interface and the grass GUI (6.4.3) to try and achieve this. Qgis interface is good but restrictive when applying extras and additions (-p/-r/-o). The GRASS GUI (6.4.3 and 7) is also fantastic but seems to lose projection along the way.

I would have thought it would be as practical[?] as:
The sum of all pixels/grid components (DEM-upper minus DEM-lower *surface area per pixel)  OR   sum of (voxel volume from lower-DEM to upper-DEM)

To the voxel end I see that the 3-D voxel data processing is not included in 6.* but is in Grass 7 (daily build version).
So, if there are no r3.* capabilities in Grass 6.4.3; which commands would one use as a substitute? Would this even apply in the 6.*-series?

Request may be a bit premature but would anyone know of a suitable website (or series thereof) that details the progression from 2-D to 3-D and then into NVIZ iro tutorials/videos?
(I have already seen the GRASS GIS series on YouTube.)

Thanks

Regards
Vinnie
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