r.out.gdal(1grass) GRASS GIS User's Manual r.out.gdal(1grass)
NAME
r.out.gdal - Exports GRASS raster maps into GDAL supported formats.
KEYWORDS
raster, export, output
SYNOPSIS
r.out.gdal
r.out.gdal --help
r.out.gdal [-lcmtf] input=name output=name format=string [type=string]
[createopt=string[,string,...]] [metaopt=string[,string,...]] [no-
data=float] [overviews=integer] [--overwrite] [--help] [--ver-
bose] [--quiet] [--ui]
Flags:
-l
List supported output formats
-c
Do not write GDAL standard colortable
Only applicable to Byte or UInt16 data types
-m
Do not write non-standard metadata
Enhances compatibility with other GIS software
-t
Write raster attribute table
Some export formats may not be supported
-f
Force raster export despite any warnings of data loss
Overrides nodata safety check
--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 raster map (or group) to export
output=name [required]
Name for output raster file
format=string [required]
Raster data format to write (case sensitive, see also -l flag)
Options: VRT, GTiff, COG, NITF, HFA, ELAS, AAIGrid, DTED, PNG,
JPEG, MEM, GIF, FITS, XPM, BMP, PCIDSK, PCRaster, ILWIS, SGI,
SRTMHGT, Leveller, Terragen, GMT, netCDF, HDF4Image, ISIS3, ISIS2,
PDS4, VICAR, ERS, JP2OpenJPEG, FIT, GRIB, RMF, WMS, RST, INGR,
GSAG, GSBG, GS7BG, R, KMLSUPEROVERLAY, WEBP, PDF, Rasterlite,
MBTiles, CALS, WMTS, MRF, PNM, PAux, MFF, MFF2, BT, LAN, IDA, LCP,
GTX, NTv2, CTable2, KRO, ROI_PAC, RRASTER, BYN, ARG, USGSDEM, BAG,
NWT_GRD, ADRG, BLX, PostGISRaster, SAGA, XYZ, HF2, JPEGLS, ZMap,
SIGDEM, GPKG, NGW, ENVI, EHdr, ISCE, Zarr
Default: GTiff
type=string
Data type
Options: Byte, Int16, UInt16, Int32, UInt32, Float32, Float64,
CInt16, CInt32, CFloat32, CFloat64
createopt=string[,string,...]
Creation option(s) to pass to the output format driver
In the form of "NAME=VALUE", separate multiple entries with a comma
metaopt=string[,string,...]
Metadata key(s) and value(s) to include
In the form of "META-TAG=VALUE", separate multiple entries with a
comma. Not supported by all output format drivers.
nodata=float
Assign a specified nodata value to output bands
If given, the nodata value is always written to metadata even if
there are no NULL cells in the input band (enhances output compati-
bility).
overviews=integer
Number of overviews to create for the output dataset
Options: 0-5
Default: 0
DESCRIPTION
r.out.gdal allows a user to export a GRASS raster map layer into any
GDAL supported raster map format. If a GRASS raster map is exported for
a particular application, the application’s native format would be
preferable. GeoTIFF is supported by a wide range of applications (see
also NOTES on GeoTIFF below).
To specify multiple creation options use a comma separated list (cre-
ateopt="TFW=YES,COMPRESS=DEFLATE").
For possible createopt and metaopt parameters please consult the indi-
vidual supported formats pages on the GDAL website. The createopt pa-
rameter may be used to create TFW or World files ("TFW=YES","WORLD-
FILE=ON").
r.out.gdal also supports the export of multiband rasters as a group,
when the imagery group’s name is entered as input. (created imagery
groups with the i.group module)
As with most GRASS raster modules, the current region extents and re-
gion resolution are used, and a MASK is respected if present. Use
g.region’s "align=", or "raster=" options if you need to realign the
region settings to match the original map’s before export.
SUPPORTED RASTER FORMATS
The set of supported raster formats written by r.out.gdal depends on
the local GDAL installation, printed with the -l flag. Available may be
(incomplete list):
AAIGrid: Arc/Info ASCII Grid
BMP: MS Windows Device Independent Bitmap
BSB: Maptech BSB Nautical Charts
DTED: DTED Elevation Raster
ELAS: ELAS
ENVI: ENVI .hdr Labelled
FIT: FIT Image
GIF: Graphics Interchange Format (.gif)
GTiff: GeoTIFF
HDF4Image: HDF4 Dataset
HFA: Erdas Imagine Images (.img)
JPEG2000: JPEG-2000 part 1 (ISO/IEC 15444-1)
JPEG: JPEG JFIF
MEM: In Memory Raster
MFF2: Atlantis MFF2 (HKV) Raster
MFF: Atlantis MFF Raster
NITF: National Imagery Transmission Format
PAux: PCI .aux Labelled
PCIDSK: PCIDSK Database File
PNG: Portable Network Graphics
PNM: Portable Pixmap Format (netpbm)
VRT: Virtual Raster
XPM: X11 PixMap Format
NOTES
Out of the GDAL data types, the closest match for GRASS CELL, FCELL and
DCELL rasters are respectively Int32, Float32 and Float64. These are
not exact equivalents, but they will preserve the maximum possible data
range and number of decimal places for each respective GRASS raster
data type. Please keep in mind that not all CELL rasters will require
Int32 - e.g., 0-255 CELL raster are covered by the Byte type as well.
Moreover, some GDAL-supported formats do not support all the data types
possible in GDAL and GRASS. Use r.info to check the data type and range
for your GRASS raster, refer to specific format documentation (on the
GDAL website), format vendor’s documentation, and e.g. the Wikipedia
article Typical boundaries of primitive integral types for details.
Ranges of GDAL data types
GDAL data type minimum maximum
Byte 0 255
UInt16 0 65,535
Int16, CInt16 -32,768 32,767
UInt32 0 4,294,967,295
Int32, CInt32 -2,147,483,648 2,147,483,647
Float32, CFloat32 -3.4E38 3.4E38
Float64, CFloat64 -1.79E308 1.79E308
If there is a need to keep file sizes small, use the simplest data type
covering the data range of the raster(s) to be exported, e.g., if suit-
able use Byte rather than UInt16; use Int16 rather than Int32; or use
Float32 rather than Float64. In addition, the COMPRESS createopt used
can have a very large impact on the size of the output file.
Some software may not recognize all of the compression methods avail-
able for a given file format, and certain compression methods may only
be supported for certain data types (depends on vendor and version).
If the export settings are set such that data loss would occur in the
output file (i.e, due to the particular choice of data type and/or file
type), the normal behaviour of r.out.gdal in this case would be to is-
sue an error message describing the problem and exit without exporting.
The -f flag allows raster export even if some of the data loss tests
are not passed, and warnings are issued instead of errors.
r.out.gdal exports may appear all black or gray on initial display in
other GIS software. This is not a bug of r.out.gdal, but often caused
by the default color table assigned by that software. The default
color table may be grayscale covering the whole range of possible val-
ues which is very large for e.g. Int32 or Float32. E.g. stretching the
color table to actual min/max would help (sometimes under symbology).
Adding overviews to speed up map display in other software
Adding overviews with gdaladdo after exporting can speed up display.
The overviews are created internally within the exported file. The
amount of levels (power-of-two factors) are controlled with the over-
views parameter. The higher the overview level defined by the user the
more lower resolution internal overviews are added Note that other
software might create their own overviews, ignoring existing overviews.
GeoTIFF caveats
GeoTIFF exports can only be displayed by standard image viewers if the
GDAL data type was set to Byte and the GeoTIFF contains either one or
three bands. All other data types and numbers of bands can be properly
read with GIS software only. Although GeoTIFF files usually have a .tif
extension, these files are not necessarily images but first of all spa-
tial raster datasets, e.g. land cover or elevation.
When writing out multi-band GeoTIFF images for users of ESRI software
or ImageMagick, the interleaving mode should be set to "pixel" using
createopt="INTERLEAVE=PIXEL". BAND interleaving is slightly more effi-
cient, but not supported by some applications. This issue only arises
when writing out multi-band imagery groups.
Classic TIFF format supports only files with up to 4GB. Files that ex-
ceed this limit (in compressed or uncompressed form) need to be ex-
ported with createopt="BIGTIFF=YES". BIGTIFF is available if GDAL is
built with libtiff &= 4.0.
Improving GeoTIFF compatibility
To create a GeoTIFF that is highly compatible with various other GIS
software packages, it is recommended to keep the GeoTIFF file as simple
as possible. You will have to experiment with which options your soft-
ware is compatible with, as this varies widely between vendors and ver-
sions. Long term, the less metadata you have to remove the more
self-documenting (and useful) the dataset will be.
Here are some things to try:
• Create a World file with createopt="TFW=YES".
• Do not use GeoTIFF internal compression. Other GIS software of-
ten supports only a subset of the available compression methods
with the supported methods differing between GIS software pack-
ages. Unfortunately this means the output image can be rather
huge, but the file can be compressed with software like zip,
gnuzip, or bzip2.
• Skip exporting the color table. Color tables are not always
properly rendered, particularly for type UInt16, and the Geo-
TIFF file can appear completely black. If you are lucky the
problematic software package has a method to reset the color
table and assign a new color table (sometimes called symbol-
ogy).
• Keep metadata simple with createopt="PROFILE=GeoTIFF" or cre-
ateopt="PROFILE=BASELINE". With BASELINE no GDAL or GeoTIFF
tags will be written and a World file is required (cre-
ateopt="TFW=YES").
EXAMPLES
Export the integer raster basin_50K map to GeoTIFF format
See also GeoTIFF format description (GDAL):
g.region raster=basin_50K -p
r.out.gdal input=basin_50K output=basin_50K.tif
Export the integer raster landclass96 map to Cloud Optimized GeoTIFF format
See also Cloud Optimized GeoTIFF (COG) format description (GDAL):
g.region -p raster=landclass96
r.out.gdal -fmt input=landclass96 output=landclass96.tif format=COG overviews=4
Export a DCELL raster map in GeoTIFF format suitable for ESRI software
g.region raster=elevation -p
r.out.gdal in=elevation output=elevation.tif createopt="PROFILE=GeoTIFF,TFW=YES"
Export a raster map in "Deflate" compressed GeoTIFF format
g.region raster=elevation -p
r.out.gdal in=elevation output=elevation.tif createopt="COMPRESS=DEFLATE"
Export a large raster map in LZW compressed (Big) GeoTIFF format
# integer map export
g.region raster=zipcodes -p
# Using PREDICTOR 2 for integer maps can further reduce file size
r.out.gdal in=zipcodes output=zipcodes.tif createopt="COMPRESS=LZW,PREDICTOR=2,BIGTIFF=YES"
# floating point map export
g.region raster=elevation -p
# Using PREDICTOR 3 for floating point data can further reduce file size
r.out.gdal in=elevation output=elevation.tif createopt="COMPRESS=LZW,PREDICTOR=3,BIGTIFF=YES"
Export a raster map with internal overview in "Deflate" compressed GeoTIFF
format
g.region raster=elevation -p
# overviews=5 corresponds to ’gdaladdo ... 2 4 8 16 32’
r.out.gdal in=elevation output=elevation.tif createopt="COMPRESS=DEFLATE" overviews=5
Export R,G,B imagery bands in GeoTIFF format suitable for ESRI software
i.group group=nc_landsat_rgb input=lsat7_2002_30,lsat7_2002_20,lsat7_2002_10
g.region raster=lsat7_2002_30 -p
r.out.gdal in=nc_landsat_rgb output=nc_landsat_rgb.tif type=Byte \
createopt="PROFILE=GeoTIFF,INTERLEAVE=PIXEL,TFW=YES"
Export group of image maps as multi-band file
g.list group
i.group group=tm7 subgroup=tm7 input=tm7_10,tm7_20,tm7_30,tm7_40,tm7_50,tm7_60,tm7_70
i.group -l tm7
g.region raster=tm7_10 -p
r.out.gdal tm7 output=lsat_multiband.tif
gdalinfo lsat_multiband.tif
Export RGB with alpha channel that encodes NULL cells
When exporting exporting RGB data rather than GIS data for Web applica-
tions or generally the scope of visualization, the alpha channel is of
use. Here the export type is commonly the Byte data type.
When exporting data with r.out.gdal, assigning a nodata value (specific
parameter of the module) means that any band values equal to this no-
data value will be interpreted as nodata. Using an additional alpha
channel means that all pixels with an alpha value of 0 are transparent.
The alpha channel thus represents per-pixel encoding of nodata, just
like the GRASS MASK (null file). That means when using an alpha chan-
nel, you do not need to "free up" any particular value, but you can use
any value you like to replace NULL cells, as long as the value can be
represented by the Byte data type. It does not matter if that value is
already present in any of the input bands.
Hence for "visual-only" RGB data export it is needed to create an addi-
tional alpha channel that encodes all NULL cells and in the RGB bands
to be exported replace NULL cells with some value in the range 0-255.
For example:
# for simplicity variables are used
RMAP="lsat7_2000_30"
GMAP="lsat7_2000_20"
BMAP="lsat7_2000_10"
OUTNAME="lsat7_2000_RGBA.tif"
# extract alpha
r.mapcalc "out_a = if(isnull($RMAP) || isnull($GMAP) || isnull($BMAP), 0, 255)"
# replace NULL cells with a valid value, extract colors
# exporting 8 bit RGB data, not GIS data, therefore the `#` operator:
r.mapcalc "out_r = if(isnull($RMAP), 0, #$RMAP)"
r.mapcalc "out_g = if(isnull($GMAP), 0, #$GMAP)"
r.mapcalc "out_b = if(isnull($BMAP), 0, #$BMAP)"
# create group for export
i.group group=out_rgba input=out_r,out_g,out_b,out_a
# remove any MASK because this works only if there are
# no NULL cells in the bands to be exported
r.mask -r
# export the group:
# add PROFILE=BASELINE to createopt to produce a standard TIFF file
# without any GTiff extensions
r.out.gdal input=out_rgba output=$OUTNAME -cm createopt="PHOTOMETRIC=RGB,ALPHA=YES"
gdalinfo $OUTNAME
The resulting GeoTIFF file can be used e.g. for Web server applica-
tions.
Export the floating point raster elevation map to ERDAS/IMG format
See also Erdas Imagine .img format description (GDAL):
g.region raster=elevation -p
r.out.gdal input=elevation output=elelevation.img format=HFA type=Float32
GDAL RELATED ERROR MESSAGES
• "ERROR 6: SetColorInterpretation() not supported for this
dataset.": This may indicate that the color table was not writ-
ten properly. But usually it will be correct and the message
can be ignored.
• "ERROR 6: SetNoDataValue() not supported for this dataset.":
The selected output format does not support "no data". It is
recommended to use a different output format if your data con-
tains NULLs.
• "Warning 1: Lost metadata writing to GeoTIFF ... too large to
fit in tag.": The color table metadata may be too large. It is
recommended to simplify or not write the color table, or use a
different output format or the flags -c and -m.
SEE ALSO
GDAL supported raster formats and GDAL supported vector formats
r.out.ascii, r.out.bin, r.out.mat, r.out.png, r.out.ppm, r.pack
REFERENCES
GDAL Pages: https://gdal.org
AUTHORS
Vytautas Vebra (oliver4grass at gmail.com)
Markus Metz (improved nodata logic)
SOURCE CODE
Available at: r.out.gdal source code (history)
Accessed: unknown
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