[Qgis-user] Volume between two surfaces

[Carlos Cerdán]

I don think so. You must do just algebraic sum: perhaps negative values are
"filling" and positive are "excavation". It depends on which layer is
subtracting.

The mask is for delimiting the area of interest only.

-----------------
What I mean in Spanish if my English is bad:

No creo que debas hacer eso. Sólo deberías hacer la suma algebraica:
tal vez los
valores negativos son "relleno" y los positivos son "excavación". Depende
de qué capa está restando.

La máscara  es  sólo para delimitar el área de interés.

--------------------

Carlos


2013/3/5 Pedro Venâncio <pedrongvenancio at yahoo.com>

> Hi Carlos,
>
> Thank you for your great tip!
>
> I was thinking... creating masks to separate the negative valuesfrom the
> positive valuesof the raster 'Hight', I can get the excavation and
> landfill volumes, right?
>
>
> Thanks!
> Pedro
>
>
>
>
>
> ----- Original Message -----
> From: Carlos Cerdán <sig.upagu at gmail.com>
> To: qgis-user at lists.osgeo.org
> Cc:
> Sent: Tuesday, March 5, 2013 11:16 PM
> Subject: Re: [Qgis-user] Volume between two surfaces
>
> One idea:
>
> Use calculator on GRASS and do:
>
> Surface 1 - Surface 2 = Hight
>
> We have the heigth value on each cell, so now use r.sum:
>
> Volume = r.sum (of Hight) * side of pixel ^2 (if cells are squares)
>
> Of course, you must use a mask to boundary your area of interest
>
> Carlos Cerdán
>
>
> El 05/03/13 17:49, Pedro Venâncio escribió:
> > 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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