Hello,
I am trying to calculate the volume of a DEM using GRASS.
For that I first calculated the area of my DEM using s.surf.area .
The result was 349 492.7m².
Then I used r.univar to get the number of cells, it is 822 244.
So the cell size is 349 492/822 244 = 0,42m²
To get the volume, I want to multiply this cell size with the total elevation value of my DEM. Where can I find this value? Is it the “sum” at the end of the r.univar report?
Otherwise, do you think my reasonning is correct to calculate the volume of a DEM?
Thank you for your help,
Marion
Hi A DEM is usually elevation above sea level, so the “volume of a DEM” would be the the total volume from sea level to the DEM elevation. Is that what you want? Usually you want the volume between two rasters: the DEM and some base elevation. So you need to begin with a simple r.mapcalc expression to get the difference bwteen the DEM and the base elevation. You can get the cell size simply from r.info Then r.univar gives the total of the cell values in it’s “sum” output. So putting it all together, i.e.: Suppose I want the volume above 150 meters: Done Yes
···
On 07/09/2018 06:05 AM, marion-brunet wrote:
Hello,
I am trying to calculate the volume of a DEM using GRASS.
For that I first calculated the area of my DEM using s.surf.area .
The result was 349 492.7m².
Then I used r.univar to get the number of cells, it is 822 244.
So the cell size is 349 492/822 244 = 0,42m²
GRASS 7.4.0 (ITM):~ > r.info -g faran_lidar | grep "res"
nsres=1
ewres=1
# Cell size of 1 meter
GRASS 7.4.0 (ITM):~ > r.info -r faran_lidar
min=73.83
max=297.64
# Min max values
# Always remember to set region
GRASS 7.4.0 (ITM):~ > g.region -p rast=faran_lidar
# Prepare the "cut" raster between 150 and the DEM
r.mapcalc "faran_cut = if(faran_lidar>150, faran_lidar, null())"
# And get the sum of all cells:
GRASS 7.4.0 (ITM):~ > r.univar faran_cut | grep sum
100%
sum: 840009490.273132
# Total 840 million cubic meters
To get the volume, I want to multiply this cell size with the total elevation value of my DEM. Where can I find this value? Is it the “sum” at the end of the r.univar report?
Otherwise, do you think my reasonning is correct to calculate the volume of a DEM?
Thank you for your help,
Marion
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Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
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