Provided by: grass-doc_7.4.0-1_all 
NAME
r.out.gdal - Exports GRASS raster maps into GDAL supported formats.
KEYWORDS
raster, export
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,...]] [nodata=float] [overviews=integer] [--overwrite] [--help]
[--verbose] [--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, NITF, HFA, ELAS, AAIGrid, DTED, PNG, JPEG, MEM, GIF, XPM, BMP, PCIDSK, PCRaster,
ILWIS, SGI, SRTMHGT, Leveller, Terragen, GMT, netCDF, HDF4Image, ISIS3, ISIS2, ERS, JP2OpenJPEG, FIT,
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, ENVI, EHdr,
ISCE, ARG, USGSDEM, NWT_GRD, ADRG, BLX, EPSILON, PostGISRaster, SAGA, XYZ, HF2, ZMap, GPKG
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 compatibility).
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 (createopt="TFW=YES,COMPRESS=DEFLATE").
For possible createopt and metaopt parameters please consult the individual supported formats pages on
the GDAL website. The createopt parameter may be used to create TFW or World files
("TFW=YES","WORLDFILE=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 region 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 suitable 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 available 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 issue 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 values 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).
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 spatial 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
efficient, but not supported by some applications. This issue only arises when writing out multi-band
imagery groups.
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
software is compatible with, as this varies widely between vendors and versions. 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 often supports only a subset of the
available compression methods with the supported methods differing between GIS software packages.
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 GeoTIFF 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 symbology).
• Keep metadata simple with createopt="PROFILE=GeoTIFF" or createopt="PROFILE=BASELINE". With
BASELINE no GDAL or GeoTIFF tags will be written and a World file is required
(createopt="TFW=YES").
• Adding overviews with gdaladdo after exporting can speed up display. Note that other software
might create their own overviews, ignoring existing overviews.
Cloud Optimized GeoTIFFs (COG) can be created with the creation options
createopt=TILED=YES,COMPRESS=DEFLATE, followed by gdaladdo to build overviews.
EXAMPLES
Export the integer raster basin_50K map to GeoTIFF format
g.region raster=basin_50K -p
r.out.gdal input=basin_50K output=basin_50K.tif
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 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 the floating point raster elevation map to ERDAS/IMG format
g.region raster=elevation -p
r.out.gdal input=elevation output=elelevation.img format=HFA type=Float32
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 applications 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 nodata 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
channel, 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 additional 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 applications.
GDAL RELATED ERROR MESSAGES
• "ERROR 6: SetColorInterpretation() not supported for this dataset.": This may indicate that the
color table was not written 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 contains
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
The GDAL supported formats page.
r.out.ascii, r.out.bin, r.out.mat, r.out.png, r.out.ppm, r.pack
REFERENCES
GDAL Pages: http://www.gdal.org
AUTHORS
Vytautas Vebra (oliver4grass at gmail.com)
Markus Metz (improved nodata logic)
Last changed: $Date: 2017-10-12 20:47:34 +0200 (Thu, 12 Oct 2017) $
SOURCE CODE
Available at: r.out.gdal source code (history)
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GRASS 7.4.0 r.out.gdal(1grass)