[Qgis-developer] Volume between two surfaces

[Pedro Venâncio]

Hi Maris,

Thank you very much!

With your directions I get the volume of landfill.

So, if I do
negative = if(diff < 0, ((diff)*(-1)), 0)

and then 
(r.sum raster=negative) * [pixel area]

I will get the volume of excavation, right?

Thanks!
Pedro




----- Original Message -----
From: Maris Nartiss 

Hello,
I would go for plain GRASS raster algebra solution.
diff = top_dem - bottom_dem # difference between two surfaces in DEM units
positive = if (diff < 0, 0, diff) # remove any errors/places where
excavation is higher than original
r.sum raster=positive
g.region -p
and multply r.sum output with size of single cell from g.region.

Take into account that large cells will produce larger uncertainty as
each cell is treated as a square prism.

Hope it helps,
Maris.

2013/3/6 Pedro Venâncio <pedrongvenancio at yahoo.com>:
> Hi all,
>
> Is there any way to calculate the volume between two surfaces (two DEM rasters)?
>
> There are ways to calculate the volume between a surface and a particular height value (GRASS r.volume or SAGA Grid Volume) but I can not find how to calculate the volumes (landfill / excavation) between two DEM.
>
> Any tips?
>
> Thank you very much!
>
> Best regards,
> Pedro Venâncio
>
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