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I have an empty raster and point shapefile (points = black dots in the image). For the analysis I use a Digital Elevation Model (DEM) with the same extent and cell size as the empty raster.

I would like to fill the empty raster cells with the elevation difference between every raster cell of the empty raster and the raster cell where the closest point is situated.

The green lines show distance between every raster cell the respective closest point.

enter image description here

Result: a raster with every cell filled difference in elevation between the cell elevation and the elevation from the cell where the point is located.

enter image description here

The first thing to know is: Which is the closest point? The distance between a raster cell and the closest point can be calculated with the distanceFromPoint tool:

r <- raster('./Raster/DEM/DEM_Refocus_5kmBuffer.tif')
s <- readOGR('./Shapefiles und CSV/River/Rive_Punkte_3035.shp')

dfp <- distanceFromPoints(r, s)

But what I actually need is the elevation differnce between every raster cell of the raster and the the points. Do you have an idea to obtain this?

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Outline solution:

  • Install the FNN package from CRAN.
  • Use nni = FNN::knnx.index(coordinates(s), coordinates(r), k=1) to get the index in s of the nearest neighbour for each cell coordinate to the points.

  • Using cellFromXY to get the cell number of each point, index that by the nearest neighbour index to pull out the value in r for each nearest point.

nelev = raster(r) # empty raster of same basis as r
nelev[] = r[cellFromXY(r, coordinates(s))[nni]]     
plot(nelev)
plot(s, add=TRUE)

gives you a raster of the value in r for the nearest point in s, which looks like a voronoi diagram (as it should).

enter image description here

You can then subtract that from r or do whatever you want with it. I've used noise for r so it looks awful if I do so I wont.

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  1. Voronoï around points as raster (find nearest raster points to given points)
  2. Migrate point DEM value to corresponding Voronoï cells (reference altitude to use for those raster points)
  3. Difference between DEM and attributed Voronoï cells (to get your required value)

Should do the trick

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