r.import(1grass) GRASS GIS User's Manual r.import(1grass)
NAME
r.import - Imports raster data into a GRASS raster map using GDAL li-
brary and reprojects on the fly.
KEYWORDS
raster, import, projection
SYNOPSIS
r.import
r.import --help
r.import [-enlo] input=name [band=integer[,integer,...]] [mem-
ory=memory in MB] [output=name] [resample=string] [extent=string]
[resolution=string] [resolution_value=float] [title=phrase]
[--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
-e
Estimate resolution only
-n
Do not perform region cropping optimization
-l
Force Lat/Lon maps to fit into geographic coordinates (90N,S;
180E,W)
-o
Override projection check (use current location’s projection)
Assume that the dataset has the same projection as the current lo-
cation
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
input=name [required]
Name of GDAL dataset to be imported
band=integer[,integer,...]
Input band(s) to select (default is all bands)
memory=memory in MB
Maximum memory to be used (in MB)
Cache size for raster rows
Default: 300
output=name
Name for output raster map
resample=string
Resampling method to use for reprojection
Options: nearest, bilinear, bicubic, lanczos, bilinear_f, bicu-
bic_f, lanczos_f
Default: nearest
nearest: nearest neighbor
bilinear: bilinear interpolation
bicubic: bicubic interpolation
lanczos: lanczos filter
bilinear_f: bilinear interpolation with fallback
bicubic_f: bicubic interpolation with fallback
lanczos_f: lanczos filter with fallback
extent=string
Output raster map extent
Options: input, region
Default: input
input: extent of input map
region: extent of current region
resolution=string
Resolution of output raster map (default: estimated)
Options: estimated, value, region
Default: estimated
estimated: estimated resolution
value: user-specified resolution
region: current region resolution
resolution_value=float
Resolution of output raster map (use with option resolution=value)
title=phrase
Title for resultant raster map
DESCRIPTION
r.import imports a map or selected bands from a GDAL raster datasource
into the current location and mapset. If the projection of the input
does not match the projection of the location, the input is reprojected
into the current location. If the projection of the input does match
the projection of the location, the input is imported directly with
r.in.gdal.
NOTES
r.import checks the projection metadata of the dataset to be imported
against the current location’s projection. If not identical a related
error message is shown.
To override this projection check (i.e. to use current location’s pro-
jection) by assuming that the dataset has the same projection as the
current location the -o flag can be used. This is also useful when geo-
data to be imported do not contain any projection metadata at all. The
user must be sure that the projection is identical in order to avoid to
introduce data errors.
Resolution
r.import reports the estimated target resolution for each input band.
The estimated resolution will usually be some floating point number,
e.g. 271.301. In case option resolution is set to estimated (default),
this floating point number will be used as target resolution. Since the
target resolution should be typically the rounded estimated resolution,
e.g. 250 or 300 instead of 271.301, flag -e can be used first to obtain
the estimate without importing the raster bands. Then the desired res-
olution is set with option resolution_value and option resolu-
tion=value. For latlong locations, the resolution might be set to arc
seconds, e.g. 1, 3, 7.5, 15, and 30 arc seconds are commonly used reso-
lutions.
Resampling methods
When reprojecting a map to a new spatial reference system, the pro-
jected data is resampled with one of four different methods: nearest
neighbor, bilinear, bicubic interpolation or lanczos.
In the following, common use cases are:
nearest is the simplest method and the only possible method for cate-
gorical data.
bilinear does linear interpolation and provides smoother output than
nearest. bilinear is recommended when reprojecting a DEM for hydrologi-
cal analysis or for surfaces where overshoots must be avoided, e.g.
precipitation should not become negative.
bicubic produces smoother output than bilinear, at the cost of over-
shoots. Here, valid pixels that are adjacent to NULL pixels or edge
pixels are set to NULL.
lanczos produces the smoothest output of all methods and preserves con-
trast best. lanczos is recommended for imagery. Both bicubic and lanc-
zos preserve linear features. With nearest or bilinear, linear features
can become zigzag features after reprojection.
In the bilinear, bicubic and lanczos methods, if any of the surrounding
cells used to interpolate the new cell value are NULL, the resulting
cell will be NULL, even if the nearest cell is not NULL. This will
cause some thinning along NULL borders, such as the coasts of land ar-
eas in a DEM. The bilinear_f, bicubic_f and lanczos_f interpolation
methods can be used if thinning along NULL edges is not desired. These
methods "fall back" to simpler interpolation methods along NULL bor-
ders. That is, from lanczos to bicubic to bilinear to nearest.
For explanation of the -l flag, please refer to the r.in.gdal manual.
When importing whole-world maps the user should disable map-trimming
with the -n flag. For further explanations of -n flag, please refer the
to r.proj manual.
EXAMPLES
Import of SRTM V3 global data at 1 arc-seconds resolution
The SRTM V3 1 arc-second global data (~30 meters resolution) are avail-
able from EarthExplorer (http://earthexplorer.usgs.gov/). The SRTM
collections are located under the "Digital Elevation" category.
Example for North Carolina sample dataset (the tile name is
"n35_w079_1arc_v3.tif"):
# set computational region to e.g. 10m elevation model:
g.region raster=elevation -p
# Import with reprojection on the fly. Recommended parameters:
# resample Resampling method to use for reprojection - bilinear
# extent Output raster map extent - region: extent of current region
# resolution Resolution of output raster map
# - region: current region resolution - limit to g.region setting from above
r.import input=n35_w079_1arc_v3.tif output=srtmv3_resamp10m resample=bilinear \
extent=region resolution=region title="SRTM V3 resampled to 10m resolution"
# beautify colors:
r.colors srtmv3_resamp10m color=elevation
Import of WorldClim data
Import of a subset from WorldClim Bioclim data set, to be reprojected
to current location projection (North Carolina sample dataset). Dif-
ferent resolutions are available, in this example we use the 2.5
arc-minutes resolution data. During import, we spatially subset the
world data to the North Carolina region using the extent parameter:
# download selected Bioclim data (2.5 arc-minutes resolution)
# optionally tiles are available for the 30 arc-sec resolution
wget http://biogeo.ucdavis.edu/data/climate/worldclim/1_4/grid/cur/bio_2-5m_bil.zip
# extract BIO1 from package (BIO1 = Annual Mean Temperature):
unzip bio_2-5m_bil.zip bio1.bil bio1.hdr
# prior to import, fix broken WorldClim extent using GDAL tool
gdal_translate -a_ullr -180 90 180 -60 bio1.bil bio1_fixed.tif
# set computational region to North Carolina, 4000 m target pixel resolution
g.region -d res=4000 -ap
# subset to current region and reproject on the fly to current location projection,
# using -n since whole-world map is imported:
r.import input=bio1_fixed.tif output=bioclim01 resample=bilinear \
extent=region resolution=region -n
# temperature data are in °C * 10
r.info bioclim01
r.univar -e bioclim01
SEE ALSO
r.in.gdal, r.proj
AUTHORS
Markus Metz
Improvements: Martin Landa, Anna Petrasova
SOURCE CODE
Available at: r.import source code (history)
Accessed: unknown
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GRASS 7.8.7 r.import(1grass)
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