Map Algebra - Grass GIS (r.mapcalc) merge two raster with NoData value

Question

I have a slope raster and a road raster. The black pixels in the road raster are NoData values and the pink pixels have a value of 1. They don't cover exactly the same area. enter image description here

I want to create a new raster based on the slope raster, except for pixels where there is a road pixel. If there is a road pixel, I want to assign a value of zero to the slope raster.

I am not quite sure how the formula needs to look like. I tried the following, put it didn't give me the expected results:

r.mapcalc "output = ((Slope+(Road*null())))"

Any ideas?

Antonio Falciano · Accepted Answer · 2014-02-21T18:42:12.560

3

Use this r.mapcalc expression:

r.mapcalc "output = not(if(Road))*Slope"

because:

if(Road)is equal to 1 if Road not zero, 0 otherwise.
not(if(Road))is equal to 0 if Road not zero, 1 otherwise.

edited Feb 21 '14 at 18:42

answered Oct 30 '13 at 20:53

Antonio Falciano

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Though the part of the Slope Raster not covered by the Road Raster gets cut off. Is there a way to keep that part? – ustroetz Oct 30 '13 at 22:24
2

You could use r.patch before in order to make the Road raster cover the lower part of the Slope raster. – Antonio Falciano Oct 30 '13 at 22:31
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more simply, g.region rast=slope. – gene Oct 31 '13 at 16:17
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Note that for GRASS 7, the command should be r.mapcalc "output = not(if(Road))*Slope" (both spaces and quotes are needed). – wenzeslaus Feb 20 '14 at 23:23
@wenzeslaus Thanks for the suggestion, I've updated the answer. – Antonio Falciano Feb 21 '14 at 18:43

Map Algebra - Grass GIS (r.mapcalc) merge two raster with NoData value

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