[GRASS-user] raster reclassification or map calculator to simulate past sea-level change

[Veronica Andreo]

Hi Erik,

IIUC, you would need something like the following:

r.mapcalc expression="bla = if(elev <= 25, 0.0, elev)"

or

r.mapcalc expression="bla = if(elev <= 25, null(), elev)"

HTH,
Vero

El mié, 10 feb 2021 a las 8:47, Erik Victor Lundstrøm (<
Victor.Lundstrom at uib.no>) escribió:

> Hi everyone,
>
> I've done some google searches related to my problem. Granted, by no
> means exhaustive, but unsuccessful nonetheless.
> Thus, I hereby by contribute with my first post in the email group
> hoping to find some help.
>
> I work in coastal Norway, and I'd like to produce different rasters
> based on estimates for when the sea-level was either higher, or lower,
> than today.
> When I started doing this years ago, it was simply enough for me to use
> the raster calculator and then produce binary maps using the "<=" or
> ">=" expression as I only wanted to visualise the difference.
> However, today I'd like to continue to work with the rasters where the
> values on the other side of the threshold that I assign remain intact
> but
> I find it way too tedious having to 1) produce a binary map, 2) convert
> the cells denoting the sea-level change into vector polygons, and then
> 3) clipping the old raster into a new one.
>
> I'll try and use an example for what I'd like to try and achieve
> instead.
>
> Let's say I have an elevation raster with values ranging from -0.001 to
> 1500m. Now, if I'd be interested in producing a raster where anything
> below 25m is submerged, then the method that I alluded
> to above would produce the following raster = 0 & 1
>
> What I'm interested in doing now instead, is to find some method where I
> still reset anything below 25m as "0", but where I still have all the
> remaining values intact.
>
> I'm thinking that there should be a way, either through the raster
> calculator or the reclassify tool, where I could simply reset anything
> above or below a certain threshold as either "0", or perhaps even "no
> data" but at the same time keep all the other elevation values of the
> raster intact.
>
> This message should hopefully be enough to indicate that I have
> relatively poor experience with both the reclassify or mapcalc-tool and
> thus any
> brief guide on how I could solve my problem would be greatly
> appreciated!
>
> If anything is unclear just let me know and I can try to reformulate.
>
> Best,
> Victor
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20210210/cc855bd0/attachment.html>