1r.external(1)                 Grass User's Manual                r.external(1)
2
3
4

NAME

6       r.external  - Links GDAL supported raster data as a pseudo GRASS raster
7       map.
8

KEYWORDS

10       raster, import, external
11

SYNOPSIS

13       r.external
14       r.external --help
15       r.external  [-fojeahvt]   [input=name]     [source=name]    output=name
16       [band=integer]    [title=phrase]   [--overwrite]  [--help]  [--verbose]
17       [--quiet]  [--ui]
18
19   Flags:
20       -f
21           List supported formats and exit
22
23       -o
24           Override projection check (use current location’s projection)
25           Assume that the dataset has same projection as the current location
26
27       -j
28           Perform projection check only and exit
29
30       -e
31           Extend region extents based on new dataset
32           Also updates the default region if in the PERMANENT mapset
33
34       -a
35           Auto-adjustment for lat/lon
36           Attempt to fix small precision errors in resolution and extents
37
38       -h
39           Flip horizontally
40
41       -v
42           Flip vertically
43
44       -t
45           List available bands including band type in dataset and exit
46           Format: band number,type,projection check
47
48       --overwrite
49           Allow output files to overwrite existing files
50
51       --help
52           Print usage summary
53
54       --verbose
55           Verbose module output
56
57       --quiet
58           Quiet module output
59
60       --ui
61           Force launching GUI dialog
62
63   Parameters:
64       input=name
65           Name of raster file to be linked
66
67       source=name
68           Name of non-file GDAL data source
69
70       output=name [required]
71           Name for output raster map
72
73       band=integer
74           Band to select (default is all bands)
75
76       title=phrase
77           Title for resultant raster map
78

DESCRIPTION

80       r.external allows a user to link a GDAL  supported  raster  file  to  a
81       binary  raster  map  layer,  from any GDAL supported raster map format,
82       with an optional title. The file is not imported but just registered as
83       GRASS raster map.
84

NOTES

86       In essence, r.external creates a read-only link to the original dataset
87       which is only valid if the original dataset remains at  the  originally
88       indicated directory and filename.
89

NULL data handling

91       GDAL-linked  (r.external)  maps do not have or use a NULL bitmap, hence
92       r.null cannot manipulate them directly. Here NULL cells are those whose
93       value  matches  the  value  reported  by the GDALGetRasterNoDataValue()
94       function.  To apply the GDAL-linked the user need to  either  create  a
95       MASK  (e.g.  with r.mask) and then "apply" it using e.g. r.resample, or
96       use r.mapcalc to create a copy with the appropriate categories  changed
97       to NULL (if() condition).
98

EXAMPLES

100   RGB Orthophoto from GeoTIFF
101       # import of all channels (each channel will become a GRASS raster map):
102       r.external input=/home/user/data/maps/059100.tif output=ortho
103       g.region raster=ortho.3 -p
104       d.rgb r=ortho.1 g=ortho.2 b=ortho.3
105       r.composite r=ortho.1 g=ortho.2 b=ortho.3 output=ortho.rgb
106
107   Processing workflow without data import and export
108       External  raster  maps  to  be  processed  can be directly linked using
109       r.external; likewise, results can be written  out  to  standard  raster
110       formats with r.external.out (GDAL supported formats):
111       # register GeoTIFF file to be used in current mapset:
112       r.external input=terra_lst1km20030314.LST_Day.tif output=modis_celsius
113       # define output directory for files resulting from GRASS calculation:
114       r.external.out directory=$HOME/gisoutput/ format="GTiff"
115       # perform GRASS calculation (here: extract pixels > 20 deg C)
116       # this stores the output map directly as GeoTIFF:
117       r.mapcalc "warm.tif = if(modis_celsius > 20.0, modis_celsius, null() )"
118       # cease GDAL output connection and turn back to write GRASS raster files:
119       r.external.out -r
120       # now use the resulting file elsewhere
121       gdalinfo $HOME/gisoutput/warm.tif
122

REFERENCES

124       GDAL Pages: http://www.gdal.org/
125

SEE ALSO

127        r.import, r.in.gdal, r.external.out
128
129        v.import, v.in.ogr, v.external, v.external.out
130

AUTHOR

132       Glynn Clements
133

SOURCE CODE

135       Available at: r.external source code (history)
136
137       Main  index  | Raster index | Topics index | Keywords index | Graphical
138       index | Full index
139
140       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
141
142
143
144GRASS 7.8.2                                                      r.external(1)