r.importgrass - Online in the Cloud

PROGRAM:

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).

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