R statistics/rgrass

Installation

See R_statistics/Installation

Terminology

See "Overview" in R_statistics

R within GRASS

In this example, we will use R within a GRASS GIS session, i.e. start R (or RStudio) from the GRASS GIS terminal or command line interface.

Startup

• First start a GRASS GIS session. Then, at the GRASS command line start R (for an 'rstudio' session, see below)

In this example we will use the North Carolina sample dataset.

Reset the region settings to the defaults

GRASS (nc_spm_08_grass7):~ > g.region -d

Launch R from the GRASS prompt

GRASS (nc_spm_08_grass7):~ > R

Load the rgrass library:

library(rgrass)

Get the GRASS environment (mapset, region, map projection, etc.); you can display the metadata for your location by printing G:

gmeta()
gisdbase    /home/mneteler/grassdata 
location    nc_spm_08_grass7 
mapset      user1 
rows        620 
columns     1630 
north       320000 
south       10000 
west        120000 
east        935000 
nsres       500 
ewres       500 
projection:
 PROJCRS["NAD83(HARN) / North Carolina",
    BASEGEOGCRS["NAD83(HARN)",
        DATUM["NAD83 (High Accuracy Reference Network)",
            ELLIPSOID["GRS 1980",6378137,298.257222101,
                LENGTHUNIT["metre",1]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433]],
        ID["EPSG",4152]],
    CONVERSION["SPCS83 North Carolina zone (meters)",
        METHOD["Lambert Conic Conformal (2SP)",
            ID["EPSG",9802]],
        PARAMETER["Latitude of false origin",33.75,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8821]],
        PARAMETER["Longitude of false origin",-79,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8822]],
        PARAMETER["Latitude of 1st standard parallel",36.1666666666667,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8823]],
        PARAMETER["Latitude of 2nd standard parallel",34.3333333333333,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8824]],
        PARAMETER["Easting at false origin",609601.22,
            LENGTHUNIT["metre",1],
            ID["EPSG",8826]],
        PARAMETER["Northing at false origin",0,
            LENGTHUNIT["metre",1],
            ID["EPSG",8827]]],
    CS[Cartesian,2],
        AXIS["easting (X)",east,
            ORDER[1],
            LENGTHUNIT["metre",1]],
        AXIS["northing (Y)",north,
            ORDER[2],
            LENGTHUNIT["metre",1]],
    USAGE[
        SCOPE["Engineering survey, topographic mapping."],
        AREA["United States (USA) - North Carolina - counties of Alamance; Alexander; Alleghany; Anson; Ashe; Avery; Beaufort; Bertie; Bladen; Brunswick; Buncombe; Burke; Cabarrus; Caldwell; Camden; Carteret; Caswell; Catawba; Chatham; Cherokee; Chowan; Clay; Cleveland; Columbus; Craven; Cumberland; Currituck; Dare; Davidson; Davie; Duplin; Durham; Edgecombe; Forsyth; Franklin; Gaston; Gates; Graham; Granville; Greene; Guilford; Halifax; Harnett; Haywood; Henderson; Hertford; Hoke; Hyde; Iredell; Jackson; Johnston; Jones; Lee; Lenoir; Lincoln; Macon; Madison; Martin; McDowell; Mecklenburg; Mitchell; Montgomery; Moore; Nash; New Hanover; Northampton; Onslow; Orange; Pamlico; Pasquotank; Pender; Perquimans; Person; Pitt; Polk; Randolph; Richmond; Robeson; Rockingham; Rowan; Rutherford; Sampson; Scotland; Stanly; Stokes; Surry; Swain; Transylvania; Tyrrell; Union; Vance; Wake; Warren; Washington; Watauga; Wayne; Wilkes; Wilson; Yadkin; Yancey."],
        BBOX[33.83,-84.33,36.59,-75.38]],
    ID["EPSG",3358]]

Listing of existing maps

List available vector maps:

execGRASS("g.list", parameters = list(type = "vector"))

List selected vector maps (wildcard):

execGRASS("g.list", parameters = list(type = "vector", pattern = "precip*"))
 precip
 precip_30ynormals
 precip_30ynormals_3d

Save selected vector maps into R vector:

my_vmaps <- execGRASS("g.list", parameters = list(type = "vector", pattern = "precip*"))
attributes(my_vmaps)
attributes(my_vmaps)$resOut
 [1] "precip"               "precip_30ynormals"    "precip_30ynormals_3d"

List available raster maps:

execGRASS("g.list", parameters = list(type = "raster"))

List selected raster maps (wildcard):

execGRASS("g.list", parameters = list(type = "raster", pattern = "lsat7_2002*"))
 lsat7_2002_10
 lsat7_2002_20
 lsat7_2002_30
 lsat7_2002_40
 lsat7_2002_50
 lsat7_2002_61
 lsat7_2002_62
 lsat7_2002_70
 lsat7_2002_80

Reading in data from GRASS

Example 1: raster maps

Manual page: read_RAST()

Read in two GRASS raster maps, "geology_30m" and "elevation", from the North Carolina sample data location into the R current session as a new object "ncdata". This object is a SpatRaster layer from terra package:

ncdata <- read_RAST(c("geology_30m", "elevation"))

We can verify the new R object:

ncdata
class       : SpatRaster 
dimensions  : 450, 500, 2  (nrow, ncol, nlyr)
resolution  : 30, 30  (x, y)
extent      : 630000, 645000, 215000, 228500  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=lcc +lat_0=33.75 +lon_0=-79 +lat_1=36.1666666666667 +lat_2=34.3333333333333 +x_0=609601.22 +y_0=0 +ellps=GRS80 +units=m +no_defs 
sources     : file1da12a752d65.grd  
              file1da12112d9ea4.grd  
names       : geology_30m, elevation 
min values  :         217,  55.92321 
max values  :         948, 156.25197

Now, let's plot one of the raster layers within the SpatRaster object. Note that we use the terra package plot function:

terra::plot(ncdata$elevation)

Add a title to the plot:

title("North Carolina elevation")

In addition, we can show what is going on inside the objects read into R:

terra::summary(ncdata)
  geology_30m      elevation     
 Min.   :217.0   Min.   : 56.01  
 1st Qu.:217.0   1st Qu.: 94.77  
 Median :270.0   Median :108.86  
 Mean   :311.2   Mean   :110.36  
 3rd Qu.:270.0   3rd Qu.:126.80  
 Max.   :948.0   Max.   :156.07

Example 2: single raster map

Here an example for a single raster map transfer from GRASS GIS to R:

library(rgrass)
execGRASS("g.region", raster = "elevation", flags = "p")
ncdata <- read_RAST("elevation")
terra::summary(ncdata)
terra::plot(ncdata)

Example 3: vector maps

Here an example for a single vector map transfer from GRASS GIS to R. In this case, vector maps from GRASS will be converted into SpatVector objects from the terra package in R:

# needed prerequisite
library(rgrass)

execGRASS("v.info", map="schools_wake", layer="1")
vInfo("schools_wake")
myschools <- read_VECT("schools_wake")
print(terra::summary(myschools))
terra::plot(myschools)

Example 4: Summarizing data

Create a box plot of geologic types at different elevations:

boxplot(ncdata$elevation ~ ncdata$geology_30m, medlwd = 1)

Example 5: Querying maps

Sometimes you may want to query GRASS GIS maps from your R session.

As an example, here the transfer of raster pixel values at the position of vector points:

# set the computational region first to the raster map:
execGRASS("g.region", raster = "elev_state_500m", flags = "p")

# query raster map at vector points, transfer result into R
goutput <- execGRASS("r.what", map="elev_state_500m", points="geodetic_pts", separator=",", intern=TRUE)
str(goutput)
chr [1:29939] "571530.81289275,265739.968425953,,187.8082200648" ...

# parse it
con <- textConnection(goutput)
go1 <- read.csv(con, header=FALSE)
str(go1)
'data.frame':	29939 obs. of  4 variables:
 $ V1: num  571531 571359 571976 572391 573011 ...
 $ V2: num  265740 265987 267049 267513 269615 ...
 $ V3: logi  NA NA NA NA NA NA ...
 $ V4: Factor w/ 22738 levels "-0.0048115728",..: 6859 6642 6749 6411 6356 6904 7506 7224 6908 7167 ...
summary(go1)
       V1               V2            V3                V4       
 Min.   :121862   Min.   :  7991   Mode:logical   0      :  723  
 1st Qu.:462706   1st Qu.:162508   NA's:29939     *      :  293  
 Median :610328   Median :204502                  0.3048 :   47  
 Mean   :588514   Mean   :200038                  0.6096 :   44  
 3rd Qu.:717610   3rd Qu.:247633                  1.524  :   42  
 Max.   :946743   Max.   :327186                  0.9144 :   23  
                                                  (Other):28767

Exporting data back to GRASS

Finally, a SpatialGridDataFrame object is written back to a GRASS raster map:

First prepare some data: (square root of elevation)

ncdata$sqdem <- sqrt(ncdata$elevation)

Export data from R back into a GRASS raster map:

writeRAST(ncdata, "sqdemNC", zcol="sqdem", ignore.stderr=TRUE)

Check that it imported into GRASS ok:

execGRASS("r.info", parameters=list(map="sqdemNC"))

 +----------------------------------------------------------------------------+
 | Map:      sqdemNC                        Date: Sun Jul 19 13:06:34 2015    |
 | Mapset:   PERMANENT                      Login of Creator: veroandreo      |
 | Location: nc_spm_08_grass7                                                 |
 | DataBase: /home/veroandreo/grassdata                                       |
 | Title:     ( sqdemNC )                                                     |
 | Timestamp: none                                                            |
 |----------------------------------------------------------------------------|
 |                                                                            |
 |   Type of Map:  raster               Number of Categories: 0               |
 |   Data Type:    DCELL                                                      |
 |   Rows:         491                                                        |
 |   Columns:      400                                                        |
 |   Total Cells:  196400                                                     |
 |        Projection: Lambert Conformal Conic                                 |
 |            N:     228500    S: 215000.0002   Res: 27.49490794              |
 |            E:     645000    W:     630000   Res:  37.5                     |
 |   Range of data:    min = 7.47818253045085  max = 12.5000787351036         |
 |                                                                            |
 |   Data Description:                                                        |
 |    generated by r.in.bin                                                   |
 |                                                                            |
 |   Comments:                                                                |
 |                                                                            |
 +----------------------------------------------------------------------------+

Using RStudio in a GRASS GIS session

If you are most used to run R through RStudio, but still want to have all GRASS data available for performing any analyses without loosing the possibility of still using GRASS command line, you can run:

GRASS> rstudio &

or, if you already are working on a certain RStudio project:

GRASS> rstudio /path/to/project/folder/ &

Then, you load rgrass library in your RStudio project

library(rgrass)

and you are ready to go.

RStudio used in GRASS GIS session

GRASS within R

Using GRASS GIS within a R session, i.e. you connect to a GRASS GIS location/mapset from within R (or RStudio).

Startup

In the first place, find out the path to the GRASS GIS library. This can be easily done with the following command (still outside of R; or through a system() call inside of R):

# OSGeo4W, Linux, Mac OSX users:
grass --config path

It may report something like:

# OSGeo4W users:
C:\OSGeo4W64\apps\grass\grass

# Linux, Mac OSX users:
/usr/local/grass

To call GRASS GIS functionality from R, start R and use the initGRASS() function to define the GRASS settings. If GRASS GIS was installed through OSGeo4W, first start the OSGeo4W Shell. Note that it may start in C: or a directory where the user does not have writing permission. Before calling R or RStudio, first change to a directory where you are sure you have writing permission.

## MS-Windows users (example for an OSGeo4W 64bit installation)
# change to a directory with writing permission
C:\>d:
D:\>cd temp
D:\temp>cd testR

# start R within this directory:
D:\temp\testR>R

# to start RStudio from OSGeo4W Shell, run: "C:/Program Files/RStudio/bin/rstudio.exe"
 
# load rgrass package
library(rgrass)

# initialisation of GRASS in the North Carolina sample dataset
initGRASS(gisBase = "C:/OSGeo4W64/apps/grass/grass",
         gisDbase = "C:/Users/marissa/grassdata/",
         location = "nc_spm_08_grass7", 
         mapset = "user1", 
         SG="elevation")

Linux and Mac OSX users just need to start R or RStudio the usual way, load the rgrass package and initialize GRASS GIS with initGRASS() as shown below:

# load rgrass package
library(rgrass)
# initialisation of GRASS in the North Carolina sample dataset
initGRASS(gisBase = "/usr/local/grass", 
          home = tempdir(), 
          gisDbase = "/home/veroandreo/grassdata/",
          location = "nc_spm_08_grass7", 
          mapset = "user1", 
          SG="elevation")

Note: the optional SG parameter is a 'SpatialGrid' object to define the ‘DEFAULT_WIND’ of the temporary location.

# set computational region to default (optional)
system("g.region -dp")
# verify metadata
gmeta()

# get two raster maps into R space
ncdata <- read_RAST(c("geology_30m", "elevation"), cat=c(TRUE, FALSE))

# calculate object summaries
summary(ncdata$geology_30m)
 CZfg_217 CZlg_262 CZig_270 CZbg_405 CZve_583 CZam_720  CZg_766 CZam_862 
     292       78      277      102        8        1        2       25 
 CZbg_910   Km_921 CZam_946     NA's 
      18        5        2  1009790

R in GRASS in batch mode

Run the following script with

R CMD BATCH batch.R

library(rgrass)
# initialisation of GRASS in the North Carolina sample dataset (example with a compiled version)
initGRASS(gisBase = "/home/veroandreo/software/grass/dist.x86_64-pc-linux-gnu", 
          home = tempdir(), 
          gisDbase = "/home/veroandreo/grassdata/",
          location = "nc_spm_08_grass7", mapset = "user1", SG="elevation",
          override = TRUE)
# set region to default
system("g.region -dp")
# verify
gmeta()
# read data into R
ncdata <- read_RAST(c("geology_30m", "elevation"), cat=c(TRUE, FALSE))
# summary of geology map
summary(ncdata$geology_30m)
proc.time()

The result is (shorted here):

cat batch.Rout

    R version 4.0.2 (2020-06-22) -- "Taking Off Again"
    Copyright (C) 2020 The R Foundation for Statistical Computing
    Platform: x86_64-redhat-linux-gnu (64-bit)
    ...
    > library(rgrass)
    Loading required package: XML
    GRASS GIS interface loaded with GRASS version: (GRASS not running)
    > # initialisation and the use of north carolina dataset
    > initGRASS(gisBase = "/home/veroandreo/software/grass/dist.x86_64-pc-linux-gnu", home = tempdir(), 
    +           gisDbase = "/home/veroandreo/grassdata/",
    +           location = "nc_spm_08_grass7", mapset = "user1", SG="elevation",
    +           override = TRUE)
    gisdbase    /home/veroandreo/grassdata/ 
    location    nc_spm_08_grass7 
    mapset      user1 
    rows        13500 
    columns     15000 
    north       228500 
    south       215000 
    west        630000 
    east        645000 
    nsres       1 
    ewres       1 
    projection  +proj=lcc +lat_1=36.16666666666666 +lat_2=34.33333333333334
    +lat_0=33.75 +lon_0=-79 +x_0=609601.22 +y_0=0 +no_defs +a=6378137
    +rf=298.257222101 +towgs84=0.000,0.000,0.000 +type=crs +to_meter=1  
    
    > system("g.region -dp")
    projection: 99 (Lambert Conformal Conic)
    zone:       0
    datum:      nad83
    ellipsoid:  a=6378137 es=0.006694380022900787
    north:      320000
    south:      10000
    west:       120000
    east:       935000
    nsres:      500
    ewres:      500
    rows:       620
    cols:       1630
    cells:      1010600
    > gmeta()
    gisdbase    /home/veroandreo/grassdata/ 
    location    nc_spm_08_grass7 
    mapset      user1 
    rows        620 
    columns     1630 
    north       320000 
    south       10000 
    ...
    > ncdata <- read_RAST(c("geology_30m", "elevation"), cat=c(TRUE, FALSE))
    ...
    > summary(ncdata$geology_30m)
    CZfg_217 CZlg_262 CZig_270 CZbg_405 CZve_583 CZam_720  CZg_766 CZam_862 
         292       78      277      102        8        1        2       25 
    CZbg_910   Km_921 CZam_946     NA's 
          18        5        2  1009790 
    > proc.time()
       user  system elapsed 
      8.061   2.016  10.048

Troubleshooting

Running out of disk space

Linux: A common issue is that /tmp/ is used for temporary files albeit being often a small partition. To change that to a larger directory, you may add to your $HOME/.bashrc the entry:

# change TMP directory of R (note: of course also another directory than suggested here is fine)
mkdir -p $HOME/tmp
export TMP=$HOME/tmp

The drawback of this approach is that on modern Linux systems the /tmp/ is a fast RAM disk (based on tempfs) while HOME directories are often on slower spinning disks (unless you have a SSD drive). At least you no longer run out of disk space easily.