Provided by: grass-doc_6.4.3-3_all bug


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


       raster, export


       r.out.gdal help
       r.out.gdal   [-lcf]    [input=name]     [format=string]     [type=string]    [output=name]
       [createopt=string[,string,...]]        [metaopt=string[,string,...]]        [nodata=float]
       [--verbose]  [--quiet]

           List supported output formats

           Do not write GDAL standard colortable
           Only applicable to Byte or UInt16 data types.

           Force raster export despite any warnings of data loss
           Overrides nodata safety check.

           Verbose module output

           Quiet module output

           Name of raster map (or group) to export

           GIS format to write (case sensitive, see also -l flag)
           Default: GTiff

           File type

           Name for output raster file

           Creation option(s) to pass to the output format driver
           In the form of "NAME=VALUE", separate multiple entries with a comma.

           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.

           Assign a specified nodata value to output bands


       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 preferrable. 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

       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 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 "rast=" options if
       you need to realign the region settings to match the original map's before export.


       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


       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
       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


   Export the integer raster roads map to GeoTIFF format:

       r.out.gdal input=roads output=roads.tif type=UInt16

   Export a DCELL raster map in GeoTIFF format suitable for ESRI software:

       r.out.gdal           in=elevation.10m           out=ned_elev10m.tif           type=Float64

   Export R,G,B imagery bands in GeoTIFF format suitable for ESRI software: group=nc_landsat_rgb input=lsat7_2002_30,lsat7_2002_20,lsat7_2002_10
       r.out.gdal          in=nc_landsat_rgb           out=nc_landsat_rgb.tif           type=Byte

   Export the floating point raster elevation map to ERDAS/IMG format:

       r.out.gdal input=elevation.10m output=elev_dem10.img format=HFA type=Float32

   Export group of image maps as multi-band file

       g.list group group=tm7 subgroup=tm7 input=tm7_10,tm7_20,tm7_30,tm7_40,tm7_50,tm7_60,tm7_70 -l tm7
       r.out.gdal tm7 type=UInt16 out=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.


       The GDAL supported formats page.
        r.out.ascii, r.out.arc, r.out.bin, r.out.mat, r.out.png, r.out.ppm, r.out.tiff (old shell script version using gdal_translate)


       GDAL Pages:


       Vytautas Vebra (oliver4grass at
       Markus Metz (improved nodata logic)

       Last changed: $Date: 2010-09-16 00:25:59 -0700 (Thu, 16 Sep 2010) $

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