Getting a raster into GRASS and back out again: `rgrass7` readRAST not preserving dimensions

Question

I am trying to get a raster into GRASS from R and back out again using the rgrass7 package. Getting the raster in seems to be no problem. However, when I try to get it out with the readRAST function it seems that the raster dimensions have been reduced to [1,1].

Am I missing a function argument? All the examples I have seen simply use the GRASS object name.

Is this a mapset issue? I didn't think so because it was my understanding that the philosophy of rgrass7 is to use temporary mapsets and layers.

See reproducible example:

library(raster)
#> Loading required package: sp

raster_image <- raster::raster(system.file("external/test.grd", package = "raster"))
raster_image <- as(raster_image, "SpatialGridDataFrame")

loc <- rgrass7::initGRASS("/usr/lib/grass70", home = tempdir(), override = TRUE)
rgrass7::writeRAST(raster_image, "raster_image", flags = c("overwrite"))
#>    0%   3%   6%   9%  12%  15%  18%  21%  24%  27%  30%  33%  36%  39%  42%  45%  48%  51%  54%  57%  60%  63%  66%  69%  72%  75%  78%  81%  84%  87%  90%  93%  96%  99% 100%
rgrass7::execGRASS("r.info", map = "raster_image")
#>  +----------------------------------------------------------------------------+
#>  | Map:      raster_image                   Date: Wed Jan 18 08:36:35 2017    |
#>  | Mapset:   file17053b43fb4e               Login of Creator: jose            |
#>  | Location: file170531b5b35a                                                 |
#>  | DataBase: /tmp/Rtmpn8cS5A                                                  |
#>  | Title:     ( raster_image )                                                |
#>  | Timestamp: none                                                            |
#>  |----------------------------------------------------------------------------|
#>  |                                                                            |
#>  |   Type of Map:  raster               Number of Categories: 0               |
#>  |   Data Type:    DCELL                                                      |
#>  |   Rows:         115                                                        |
#>  |   Columns:      80                                                         |
#>  |   Total Cells:  9200                                                       |
#>  |        Projection: x,y                                                     |
#>  |            N:     334000    S:     329400   Res:    40                     |
#>  |            E:     181600    W:     178400   Res:    40                     |
#>  |   Range of data:    min = 128.434005737305  max = 1805.78002929688         |
#>  |                                                                            |
#>  |   Data Description:                                                        |
#>  |    generated by r.in.bin                                                   |
#>  |                                                                            |
#>  |   Comments:                                                                |
#>  |    r.in.bin --overwrite -d input="/tmp/Rtmpn8cS5A/file170531b5b35a/file\   |
#>  |    17053b43fb4e/.tmp/josecomp/X530" output="raster_image" bytes=8 heade\   |
#>  |    r=0 bands=1 order="native" north=334000 south=329400 east=181600 wes\   |
#>  |    t=178400 rows=115 cols=80 anull=127                                     |
#>  |                                                                            |
#>  +----------------------------------------------------------------------------+

out_raster <- rgrass7::readRAST("raster_image")
#> Creating BIL support files...
#> Exporting raster as floating values (bytes=8)
#>    0% 100%
dim(raster_image)
#> [1] 9200    1
plot(raster_image)

dim(out_raster)
#> [1] 1 1
plot(out_raster)
#> Warning in min(x): no non-missing arguments to min; returning Inf
#> Warning in max(x): no non-missing arguments to max; returning -Inf
#> Error in seq.default(zlim[1], zlim[2], length.out = length(col) + 1): 'from' cannot be NA, NaN or infinite

Answer 1

Your GRASS mapset region settings are at fault (even a temp dir needs to be set up). Try something like

region_check <- capture.output(execGRASS('g.region', flags = c('p'))

edit: (nah, just use `gmeta()` )

or cheat: open your mapset directly in GRASS and run g.region -p. You can do this even with a temp location so long as you don't exit R, you just have to navigate to the correct R temp folder in GRASS's start screen.

You will be able to set the region to match the file you imported by e.g. g.region raster=raster_image'.

edit2: you may find that after this, the location still has no genuine CRS. g.region won't set that, instead you need to run g.proj -t -c georef='raster_image' or similar. The catch is that this has to be done in the PERMANENT mapset and then g.region -d has to be run in all other mapsets.

Suggest you simplify your life by altering your initGRASS call to start in PERMANENT e.g.

rgrass7::initGRASS("/usr/lib/grass70", home = tempdir(), 
                   mapset = 'PERMANENT', override = TRUE)

I've never understood why that isn't default behaviour in GRASS. Anyway, you can then set projection with g.proj. Notably, if you point it at a raster on disk using the georef= parameter (e.g. georef=<filepath> or georef=raster@file@name), you get all your region settings matching the file, not just the projection.