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NAME
r.import - Imports raster data into a GRASS raster map using GDAL library and reprojects on the fly.
KEYWORDS
raster, import, projection
SYNOPSIS
r.import
r.import --help
r.import [-enl] input=name [band=integer[,integer,...]] [memory=integer] output=name
[resample=string] [extent=string] [resolution=string] [resolution_value=float] [--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)
--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=integer
Maximum memory to be used (in MB)
Cache size for raster rows
Options: 0-2047
Default: 300
output=name [required]
Name for output raster map
resample=string
Resampling method to use for reprojection
Options: nearest, bilinear, bicubic, lanczos, bilinear_f, bicubic_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)
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
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 resolution is set
with option resolution_value and option resolution=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 resolutions.
Resampling methods
When reprojecting a map to a new spatial reference system, the projected data is resampled with one of
four different methods: nearest neighbor, bilinear, bicubic iterpolation or lanczos.
In the following common use cases:
nearest is the simplest method and the only possible method for categorical data.
bilinear does linear interpolation and provides smoother output than nearest. bilinear is recommended
when reprojecting a DEM for hydrological 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 overshoots.
lanczos produces the smoothest output of all methods and preserves contrast best. lanczos is recommended
for imagery. Both bicubic and lanczos preserve linear features. With nearest or bilinear, linear
features can become zigzag features after reprojection.
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.
EXAMPLE
Import of a subset from Bioclim data set, to be reprojected to current location projection (North
Carolina sample dataset). While normally the full raster map is imported, we spatially subset using the
extent parameter:
# download selected Bioclim data
wget http://biogeo.ucdavis.edu/data/climate/worldclim/1_4/grid/cur/bio_2-5m_bil.zip
# extract BIO1 from package:
unzip bio_2-5m_bil.zip bio1.bil bio1.hdr
# 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.bil output=bioclim01 resample=bilinear \
extent=region resolution=region -n
r.info bioclim01
r.univar -e bioclim01
KNOWN ISSUES
The option extent=region only works when the dataset has a different projection than the current location
(i.e., internally r.proj is invoked).
SEE ALSO
r.in.gdal, r.proj
AUTHORS
Markus Metz
Improvements: Martin Landa, Anna Petrasova
Last changed: $Date: 2015-01-20 20:52:27 +0100 (Tue, 20 Jan 2015) $
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