Merging raster in R

Question

I am trying to merge seven tiles of raster in R version 4.0.3 but it shows error as:

Error in compareRaster(x, extent = FALSE, rowcol = FALSE, orig = TRUE,  : 
  different origin.

The origin of raster are:

> origin(f1)
[1] 1.549293 0.000000
> origin(f2)
[1] 1.666904 2.306145
> origin(f3)
[1]  0.02155916 -0.67734774
> origin(f4)
[1] 2.921843 4.800345
> origin(f5)
[1] -2.036317 -1.870532
> origin(f6)
[1] 3.293903 4.393251
> origin(f7)
[1] -0.3293477 -0.2457405

and I tried tolerance=0.1 but its still showing the same error. The R code is here:

library(raster)
merge_forest <- raster::merge(f1,f2,f3,f4,f5,f6,f7,tolerance=0.1)

These are the raster tiles of landcover(https://www.arcgis.com/apps/instant/media/index.html?appid=fc92d38533d440078f17678ebc20e8e2&fbclid=IwAR3Y3SN7iyaPrzViPzagVH086dZTygvmwoIdZrudbb4EJlJyZOf6zdA13g4).

I downloaded seven tiles that covers the area of Norway and wanted to merge it together and clip it to the extent of Norway.

Answer 1

The terra package has a new object class SpatRasterCollection for image collections than can be used with terra::mosaic or terra::merge. This greatly simplifies mosaic operations. Here is an example where we: 1) create a vector of raster files; 2) use lapply to create raster objects wrapped in terra::src to create a SpatRasterCollection; 3) pass the image collection to the terra::mosaic function.

library(terra)
img <- list.files(getwd(), "tif$", full.names=TRUE) # the $ exludes aux-files
  ic <- sprc(lapply(img, rast))
    r <- mosaic(ic)

Answer 2

Lets consider only tile 32V and 32W.

I tried to create a R script to mosaic those tiles, but it takes too long to compile because of the resample process (10m resolution for Norway extent)...

So I used GDAL:

gdalbuildvrt mosaic.vrt 32V_20200101-20210101.tif 32W_20200101-20210101.tif

Where mosaic.vrt is the output and 32V_20200101-20210101.tif 32W_20200101-20210101.tif are the inputs (you can include all 7 tiles).

gdal_translate mosaic.vrt MOSAIC.tif

Where mosaic.vrt is the input (previously created) and MOSAIC.tif is the output in tif format.

I opened the MOSAIC in R:

library(raster)

Mosaic <- "MOSAIC.tif"
RasterM <- raster(Mosaic)
plot(RasterM)

Check if this is what you are looking for. I can share my R script but I don't know the final result because it takes a lot of time to compile.

Answer 3

You stand a better chance of getting the right solution or help by providing the code you used and some details of your raster data. Without it is difficult to be of help.

Without knowing the purpose of the merge, the solution below might be of help

merged_f <- merge(f1 ... f7, fun = ) #insert the function you want to use e.g sum, mean etc

If the purpose is to create a mosaic (considering the extent of the rasters) then below by SpatialProgramming (see https://stackoverflow.com/questions/50740097/merge-rasters-of-different-extents-sum-overlapping-cell-values-in-r), might help

merged_f <- mosaic(f1 ... f7, fun = )