r.out.gdal(1)

📦
version 8.4.2 · 9 versions
, in fedora 44

✨ r.out.gdal ✨

okay bestie, gather round, because r.out.gdal is the GRASS GIS module that takes your raster and yeets it into literally any GDAL-supported format. it's giving ✨export era✨ and we're gonna go through every single flag together, no skipping, no cap 💅

🌸 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,...]]
[nodata=float]   [overviews=integer]   [offset=float]   [scale=float]
[--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

🎀 Flags 🎀

  • -l — list supported output formats 👑 (do this first, trust me)
  • -c — do not write GDAL standard colortable. only applies to Byte or UInt16 data types.
  • -m — do not write non-standard metadata. this one enhances compatibility with other GIS software 🫶
  • -t — write raster attribute table. lowkey, some export formats may not be supported 🙈
  • -f — force raster export despite any warnings of data loss. this one overrides the nodata safety check, so be careful bestie 😭
  • --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: GTiff, COG, VRT, NITF, HFA, AAIGrid, DTED, PNG, GTA, JPEG, MEM, GIF, FITS, BMP, PCIDSK, PCRaster, ILWIS, SRTMHGT, Leveller, Terragen, netCDF, HDF4Image, ISIS3, PDS4, VICAR, ERS, JP2OpenJPEG, GRIB, RMF, WMS, RST, GSAG, GSBG, GS7BG, KMLSUPEROVERLAY, WEBP, PDF, MBTiles, CALS, WMTS, MRF, PNM, BT, LCP, GTX, KRO, ROI_PAC, RRASTER, BAG, NWT_GRD, PostGISRaster, SAGA, XYZ, HF2, ZMap, SIGDEM, EXR, GPKG, OpenFileGDB, 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, so vibe check first 💀
  • 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

  • offset=float — assign a specified offset value to output bands
  • scale=float — assign a specified scale value to output bands

💖 DESCRIPTION 💖

r.out.gdal lets a user export a GRASS raster map layer into any GDAL supported raster map format. the way that this works is so iconic — if you're exporting a GRASS raster map 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. fr fr, don't skip this step.

🌈 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
bestie reminder: this is an incomplete list. your actual local set is whatever -l tells you 💅

🧚 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 ⭐

  • Byte — minimum 0, maximum 255
  • UInt16 — minimum 0, maximum 65,535
  • Int16, CInt16 — minimum -32,768, maximum 32,767
  • UInt32 — minimum 0, maximum 4,294,967,295
  • Int32, CInt32 — minimum -2,147,483,648, maximum 2,147,483,647
  • Float32, CFloat32 — minimum -3.4E38, maximum 3.4E38
  • Float64, CFloat64 — minimum -1.79E308, maximum 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. ⚠️

no cap: -f means warnings instead of errors. you were warned, bestie.

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). 💀 not your fave, I know.

🎀 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 overviews 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 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.

Classic TIFF format supports only files with up to 4GB. Files that exceed this limit (in compressed or uncompressed form) need to be exported 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 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").

💅 Offset/scale parameters 💅

Offset is only relevant if not zero. Scale is only relevant if not 1. periodt.

🎀 EXAMPLES 🎀

okay bestie this is the part where it all clicks, like the moment in a rom-com where everything makes sense 💖 every single one of these is copy-paste-ready, so go off.

🗺️ 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 you're exporting exporting RGB data rather than GIS data — think Web applications, or honestly just anything where the vibe is visualization — the alpha channel is your bestie. Here the export type is commonly the Byte data type. 💅

When you export data with r.out.gdal, assigning a nodata value (that's a specific parameter of this module, iykyk) means any band values equal to that nodata value get interpreted as nodata. But if you use an additional alpha channel, then all pixels with an alpha value of 0 are transparent. So the alpha channel is basically per-pixel encoding of nodata, just like the GRASS MASK (null file). Which means: when you're using an alpha channel, you do not need to "free up" any particular value — you can use literally any value you like to replace NULL cells, as long as that value can be represented by the Byte data type. And it does not matter if that value is already present in any of the input bands. no cap. ✨

So for "visual-only" RGB data export you need to create an additional alpha channel that encodes all NULL cells, and in the RGB bands being 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. 🫶

🛰️ 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

📐 Export raster map with offset/scale assigned

An offset value can be assigned to output raster data by the offset parameter. Similarly, a scale value can be assigned by the scale parameter.

# produce raster map
g.region n=100 s=0 e=100 w=0 res=1
r.random.cells output=random distance=1.0
r.info -r random
# export raster data with offset/scale assigned
r.out.gdal input=random output=random.tif offset=100 scale=0.01

Check result by gdalinfo command line tool:

gdalinfo random.tif
...
Band 1 Block=100x40 Type=UInt16, ColorInterp=Palette
  Description = random
    Computed Min/Max=1.000,3661.000
  NoData Value=65535
  Offset: 100,   Scale:0.01
...

ngl when GDAL starts yelling at you, don't panic — here's the translation:

  • "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 just be ignored. lowkey harmless 🙈
  • "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. fr fr, pick another format.
  • "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 use the flags -c and -m.

🌈 REFERENCES 🌈

GDAL Pages: https://gdal.org

👀 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

👑 AUTHORS 👑

  • Vytautas Vebra (oliver4grass at gmail.com)
  • Markus Metz (improved nodata logic)

📜 SOURCE CODE 📜

Available at: r.out.gdal source code (history)

Accessed: Saturday Jan 17 05:40:52 2026

Main index | Raster index | Topics index | Keywords index | Graphical index | Full index

okay that's the whole page bestie, you're officially a r.out.gdal girlie now 💖 this was the GRASS GIS 8.4.2 Reference Manual, © 2003-2025 GRASS Development Team, and the page you just read is GRASS 8.4.2 — r.out.gdal(1). go export something iconic 🦋✨

📦 where this page comes from