A raster is just a matrix of elevations. Each element of that matrix has a
horizontal area. If you subtract that elevation from a reference elevation and
zero out all negative values then you are left with a bunch of rectangular
parallelopipeds of varying height. Add those heights up and multiply by the
scalar area of the parallelopipeds and you have the volume. Repeat this for
various elevations and form a set of estimates of volume vs elevation. You can
use approxfun or splinefun to create a function from those points for more
general use.
There are some subtleties such as converting between elevation and depth, and
whether you are concerned about disjoint depressions (they would not drain)...
but OP really should have read the posting guide and asked this question on
R-sig-geo mailing list.
On December 5, 2023 9:09:12 PM PST, Bert Gunter <bgunter.4...@gmail.com> wrote:
>The volume of a polygon = 0. Polyhedra have volumes.
>
>This may be irrelevant, but if the lake is cylindrical == constant cross
>sectional area at all depths, then height doubles when the volume does and
>vice versa. Otherwise you have to know how area varies with height or use
>more sensible approximations thereto.
>
>Cheers,
>Bert
>
>On Tue, Dec 5, 2023, 20:13 javad bayat <j.bayat...@gmail.com> wrote:
>
>> Dear all;
>> I am trying to calculate the volume of a polygon shapefile according to a
>> DEM raster. I have provided some codes at the end of this email.I dont know
>> if the codes are correct or not. Following this, I have another question
>> too.
>> I want to know if the volume of the reservoir rises or doubles, what would
>> be the elevation?
>> I would be more than happy if anyone could help me.
>> Sincerely
>>
>> "
>> library(raster)
>> library(terra)
>> library(exactextractr)
>> library(dplyr)
>> library(sf)
>> r <- raster("Base.tif")
>> p <- shapefile("p.shp")
>> r <- crop(r, p)
>> r <- mask(r, p)
>> x <- exact_extract(r, p, coverage_area = TRUE)
>>
>> x1 = as.data.frame(x[1])
>> head(x1)
>> x1 = na.omit(x1)
>>
>> x1$Height = max(x1[,1]) - x1[,1]
>>
>> x1$Vol = x1[,2] * x1[,3]
>>
>> sum(x1$Vol)
>>
>> "
>>
>> --
>> Best Regards
>> Javad Bayat
>> M.Sc. Environment Engineering
>> Alternative Mail: bayat...@yahoo.com
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> [[alternative HTML version deleted]]
>
>______________________________________________
>R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
--
Sent from my phone. Please excuse my brevity.
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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