R statistics/rgrass7

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This page refers to the usage of R within a GRASS GIS 7 session. (see also R_statistics/spgrass6)

Startup

  • First start a GRASS GIS session. Then, at the GRASS command line start R (for a 'rstudio' session, see below)
In this example we will use the North Carolina sample dataset.

Reset the region settings to the defaults

GRASS 7.0.1svn (nc_spm_08_grass7):~ > g.region -d

Launch R from the GRASS prompt

GRASS 7.0.1svn (nc_spm_08_grass7):~ > R

Load the rgrass7 library:

> library(rgrass7)

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

> gmeta()
gisdbase    /home/neteler/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  +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 +to_meter=1 

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*"))

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

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_2000*"))

Reading in data

Read in two raster maps (North Carolina sample dataset):

> ncdata <- readRAST(c("geology", "elevation"),
           cat=c(TRUE, FALSE), ignore.stderr=TRUE,
           plugin=NULL)

The metadata are accessed and available, but are not (yet) used to structure the sp class objects, here a SpatialGridDataFrame object filled with data from two Spearfish layers. Here is a plot of the elevation data:

> image(spear, attr = 2, col = terrain.colors(20))

Add a title to the plot:

> title("Spearfish elevation")
R stats elev.png

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

> str(G)
List of 26
 $ GISDBASE     : chr "/home/rsb/topics/grassdata"
 $ LOCATION_NAME: chr "spearfish57"
 $ MAPSET       : chr "rsb"
 $ DEBUG        : chr "0"
 $ GRASS_GUI    : chr "text"
 $ projection   : chr "1 (UTM)"
 $ zone         : chr "13"
 $ datum        : chr "nad27"
 $ ellipsoid    : chr "clark66"
 $ north        : num 4928010
 $ south        : num 4913700
 $ west         : num 589980
 $ east         : num 609000
 $ top          : num 1
 $ bottom       : num 0
 $ nsres        : num 30
 $ nsres3       : num 30
 $ ewres        : num 30
 $ ewres3       : num 30
 $ tbres        : num 1
 $ rows         : int 477
 $ rows3        : int 477
 $ cols         : int 634
 $ cols3        : int 634
 $ depths       : int 1
 $ proj4        : chr "+proj=utm +zone=13 +a=6378206.4 +rf=294.9786982 +no_defs +nadgrids=/home/rsb/topics/grass61/grass-6.1.cvs/etc/nad/conus"


> summary(spear)
Object of class SpatialGridDataFrame
Coordinates:
              min     max
coords.x1  589980  609000
coords.x2 4913700 4928010
Is projected: TRUE 
proj4string : [+proj=utm +zone=13 +a=6378206.4 +rf=294.9786982 +no_defs +nadgrids=/home/rsb/topics/grass61/grass-6.1.cvs/etc/nad/conus]
Number of points: 2
Grid attributes:
  cellcentre.offset cellsize cells.dim
1            589995       30       634
2           4913715       30       477
Data attributes:
      geology      elevation.dem  
 sandstone:74959   Min.   : 1066  
 limestone:61355   1st Qu.: 1200  
 shale    :46423   Median : 1316  
 sand     :36561   Mean   : 1354  
 igneous  :36534   3rd Qu.: 1488  
 (Other)  :37636   Max.   : 1840  
 NA's     : 8950   NA's   :10101  

Summarizing data

We can create a table of cell counts:

> table(spear$geology)
metamorphic transition igneous sandstone limestone shale sandy shale claysand sand
11693 142 36534 74959 61355 46423 11266 14535 36561

And compare with the equivalent GRASS module:

> execGRASS("r.stats", flags=c("c", "l"), parameters=list(input="geology"), ignore.stderr=TRUE)
1 metamorphic 11693
2 transition 142
3 igneous 36534
4 sandstone 74959
5 limestone 61355
6 shale 46423
7 sandy shale 11266
8 claysand 14535
9 sand 36561
* no data 8950


Create a box plot of geologic types at different elevations:

> boxplot(spear$elevation.dem ~ spear$geology, medlwd = 1)
R stats boxplot geo.png

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)

> spear$sqdem <- sqrt(spear$elevation.dem)

Export data from R back into a GRASS raster map:

> writeRAST6(spear, "sqdemSP", zcol="sqdem", ignore.stderr=TRUE)

Check that it imported into GRASS ok:

> execGRASS("r.info", parameters=list(map="sqdemSP"))
 +----------------------------------------------------------------------------+
 | Layer:    sqdemSP                        Date: Sun May 14 21:59:26 2006    |
 | Mapset:   rsb                            Login of Creator: rsb             |
 | Location: spearfish57                                                      |
 | DataBase: /home/rsb/topics/grassdata                                       |
 | Title:     ( sqdemSP )                                                     |
 |----------------------------------------------------------------------------|
 |                                                                            |
 |   Type of Map:  raster              Number of Categories: 255              |
 |   Data Type:    FCELL                                                      |
 |   Rows:         477                                                        |
 |   Columns:      634                                                        |
 |   Total Cells:  302418                                                     |
 |        Projection: UTM (zone 13)                                           |
 |            N:    4928010    S:    4913700   Res:    30                     |
 |            E:     609000    W:     589980   Res:    30                     |
 |   Range of data:    min =  32.649654 max = 42.895222                       |
 |                                                                            |
 |   Data Source:                                                             |
 |                                                                            |
 |                                                                            |
 |                                                                            |
 |   Data Description:                                                        |
 |    generated by r.in.gdal                                                  |
 |                                                                            |
 |                                                                            |
 +----------------------------------------------------------------------------+