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

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

   Flags:
       -l
           List supported output formats

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

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

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Name of raster map (or group) to export

       format=string
           GIS 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,JPEG2000,FIT,RMF,WMS,RST,INGR,GSAG,GSBG,GS7BG,R,PNM,ENVI,EHdr,PAux,MFF,MFF2,BT,LAN,IDA,GTX,NTv2,CTable2,ARG,USGSDEM,ADRG,BLX,Rasterlite,EPSILON,PostGISRaster,SAGA,KMLSUPEROVERLAY,XYZ,HF2,PDF,ZMap
           Default: GTiff

       type=string
           File type
           Options: Byte,Int16,UInt16,Int32,UInt32,Float32,Float64,CInt16,CInt32,CFloat32,CFloat64

       output=name
           Name for output raster file

       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
       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 (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 "rast=" 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 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 createopt="PROFILE=GeoTIFF,TFW=YES"

   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
       r.out.gdal               in=nc_landsat_rgb                out=nc_landsat_rgb.tif                type=Byte
       createopt="PROFILE=GeoTIFF,INTERLEAVE=PIXEL,TFW=YES"

   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
       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
       r.out.gdal tm7 type=UInt16 out=lsat_multiband.tif
       gdalinfo lsat_multiband.tif

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.

REFERENCES

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

AUTHORS

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

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

       Full index

       © 2003-2013 GRASS Development Team

GRASS 6.4.3                                                                                   r.out.gdal(1grass)