Ubuntu Manpage: r.out.gdal - Exports GRASS raster maps into GDAL supported formats.

name
keywords
synopsis
description
supported raster formats
notes
examples
gdal related error messages
see also
references
authors

Provided by: grass-doc_7.0.3-1build1_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  [-lctf] input=name output=name format=string  [type=string]   [createopt=string[,string,...]]
       [metaopt=string[,string,...]]   [nodata=float]   [--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

       -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, ISIS2, ERS, JP2OpenJPEG, FIT,
           JPEG2000, RMF, WMS, RST, INGR, GSAG, GSBG, GS7BG, R, PNM, ENVI, EHdr, PAux, MFF, MFF2, BT, LAN,  IDA,
           LCP,  GTX,  NTv2,  CTable2,  KRO,  ARG, USGSDEM, ADRG, BLX, Rasterlite, EPSILON, PostGISRaster, SAGA,
           KMLSUPEROVERLAY, XYZ, HF2, PDF, WEBP, ZMap
           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

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.
       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. SRTM DEM version 4.

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.

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

           •   "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.

REFERENCES

       GDAL Pages: http://www.gdal.org

AUTHORS

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

       Last changed: $Date: 2015-12-31 09:19:51 +0100 (Thu, 31 Dec 2015) $

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