Provided by: grass-doc_8.4.0-1_all 
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 [-enlo] input=name [band=integer[,integer,...]] [memory=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 project’s CRS)
Assume that the dataset has the same coordinate reference system (CRS) as the current
project
--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, 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)
title=phrase
Title for resultant raster map
DESCRIPTION
r.import imports a map or selected bands from a GDAL raster datasource into the current
project (previously called location) and mapset. If the coordinate reference system (CRS)
of the input does not match the CRS of the project, the input is reprojected into the
current project. If the CRS of the input does match the CRS of the project, the input is
imported directly with r.in.gdal.
NOTES
r.import checks the CRS metadata of the dataset to be imported against the current
project’s CRS. If not identical a related error message is shown.
To override this projection check (i.e. to use current project’s CRS) by assuming that the
dataset has the same CRS as the current project the -o flag can be used. This is also
useful when geodata to be imported do not contain any CRS metadata at all. The user must
be sure that the CRS is identical in order to avoid introducing 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 resolution is set with
option resolution_value and option resolution=value. For latlong projects, 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 interpolation or
lanczos.
In the following, common use cases are:
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. 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 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.
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 areas 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 borders. 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 available 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 project
CRS (North Carolina sample dataset). Different 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 project CRS,
# 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: Thursday Aug 01 11:31:52 2024
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