[R-sig-Geo] clip a raster layer to a mask layer using raster algebra in R?

[Hugo Costa]

Possibly there are alternatives, like exploring raster::overlay together
with raster:clusterR
Hugo

Christian Willmes <c.willmes using uni-koeln.de> escreveu no dia quinta,
6/12/2018 à(s) 13:34:

> Thank you.
>
> It seems that both approaches need an additional, very expensive
> computation (takes several minutes on a i7-4790 with SSD) to create the
> mask or the extent, and in my case the mask computed by this command
> below is already what I want. Only values above a given RSL (Sealevel)
> height. The rest of the raster needs to be NA or NULL.
>
>  >gebco_rsl <- gebco
>  >gebco_rsl[gebco < rsl] <- NA
>
> ....
>
> The easy (and faster) approach for creating a mask:
>
>  >gebco_mask <- gebco >= rsl
>
> writes 0's into the remaining cells, which does not work for me (and the
> mask() function).
>
> On the other hand, the GRASS mapcalc computation (given below) takes
> less than a minute on that same raster.
>
> I wanted to re-implement the whole analysis in R for better/easier
> reproducibility, but now I think I will stick to R + GRASS GIS.
>
> If anyone knows a faster approach for creating a mask in R, please let
> me know.
>
> Thanks and best regards,
> Christian
>
> Am 06.12.18 um 10:59 schrieb Bede-Fazekas Ákos:
> > Dear Christian,
> > raster::mask() and raster::crop() may solve your problem.
> >
> https://www.rdocumentation.org/packages/raster/versions/2.8-4/topics/mask
> >
> https://www.rdocumentation.org/packages/raster/versions/2.8-4/topics/crop
> >
> > HTH,
> > Ákos Bede-Fazekas
> > Hungarian Academy of Sciences
> >
> > 2018.12.06. 9:40 keltezéssel, Christian Willmes írta:
> >> Sorry, I had an error in the main command.
> >>
> >> It should be:
> >>
> >> gebco_clipped <- ifelse(RSLmask, gebco, NA)
> >>
> >> But it still gives the same error.
> >>
> >> Best,
> >> Christian
> >>
> >> Am 06.12.18 um 09:37 schrieb Christian Willmes:
> >>> Hello,
> >>>
> >>> this should be normally a very basic simple one-liner, but I can't
> >>> get my head around it. I only find solutions for cliping a raster
> >>> against a vector, but none for clipping a raster against a raster mask.
> >>>
> >>> I want to clip a layer to a mask. In GRASS GIS r.mapcalc the syntax is:
> >>>
> >>> result = if(RSLmask, gebco, null())
> >>>
> >>> This clips the GEBCO dataset to the extent of the given raster mask
> >>> 'rslmask'. The result raster has heigt values within the raster mask
> >>> extent, the rest of the raster layer has NULL or NA values.
> >>>
> >>> In R I did the following, but it does not work as expected:
> >>>
> >>> gebco <- raster(gebco2014) #load raster
> >>>
> >>> RSLmask <- gebco >= 0  #create mask layer
> >>>
> >>> RSL <- ifelse(RSLmask, 1, NA)
> >>>
> >>> The last command gives an error about vector type 'S4'?!
> >>>
> >>> >In is.na(test) :
> >>>   >is.na() auf nicht-(Liste oder Vektor) des Typs 'S4' angewendet
> >>>
> >>> So, in short: what is the R way to simply clip a raster to a raster
> >>> mask?
> >>>
> >>> Thanks and best regards,
> >>> Christian
> >>>
> >>> PS: If found many solutions for clipping a raster to a vector
> >>> polygon, but this is not what I want.
> >>>
> >
> > _______________________________________________
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> > R-sig-Geo using r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
> --
> Dr. Christian Willmes
> AG GIS & Fernerkundung      | GIS & RS Group
> Geographisches Institut     | Institute of Geography
> Universität zu Köln         | University of Cologne
> Tel.: +49 (0)221 470 6234
> http://www.geographie.uni-koeln.de/14126.html
> http://www.sfb806.de
> http://crc806db.uni-koeln.de
> http://publons.com/a/1316706/
> http://orcid.org/0000-0002-5566-6542
>
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