DESCRIPTION
r.out.gdal allows a user to export a GRASS raster map layer
into any GDAL supported raster map format.
For possible metaopt parameters see 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
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.
Some software may not recognize all of the compression methods available.
To specify multiple options use a comma separated list
(createopt="TFW=YES,COMPRESS=DEFLATE").
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.
Improving GeoTIFF compatibility
To create a highly compatibility GeoTIFF 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 and the GeoTIFF file can appear completely black. If you are lucky
the problematic software package has a method to reset the color table.
- 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="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="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.
SEE ALSO
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
r.out.gdal.sh
(old shell script version using gdal_translate)
REFERENCES
GDAL Pages: http://www.gdal.org
AUTHOR
Vytautas Vebra (oliver4grass at gmail.com)
Last changed: $Date$