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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     [-lcmtf]     input=name     output=name     format=string     [type=string]
       [createopt=string[,string,...]]        [metaopt=string[,string,...]]        [nodata=float]
       [overviews=integer]   [--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

       -m
           Do not write non-standard metadata
           Enhances compatibility with other GIS software

       -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,
           ISIS3,  ISIS2,  ERS,  JP2OpenJPEG,  FIT,  RMF,  WMS,  RST, INGR, GSAG, GSBG, GS7BG, R,
           KMLSUPEROVERLAY, WEBP, PDF, Rasterlite, MBTiles, CALS,  WMTS,  MRF,  PNM,  PAux,  MFF,
           MFF2,  BT,  LAN,  IDA,  LCP,  GTX, NTv2, CTable2, KRO, ROI_PAC, ENVI, EHdr, ISCE, ARG,
           USGSDEM, NWT_GRD, ADRG, BLX, EPSILON, PostGISRaster, SAGA, XYZ, HF2, ZMap, GPKG
           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
           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

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, 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

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. 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.

   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.

       Cloud   Optimized   GeoTIFFs   (COG)   can   be   created   with   the   creation  options
       createopt=TILED=YES,COMPRESS=DEFLATE, followed by gdaladdo to build 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

   Export RGB with alpha channel that encodes NULL cells
       When exporting exporting RGB data rather than GIS data for Web applications  or  generally
       the  scope of visualization, the alpha channel is of use. Here the export type is commonly
       the Byte data type.

       When exporting data with r.out.gdal, assigning a nodata value (specific parameter  of  the
       module)  means  that  any  band  values  equal to this nodata value will be interpreted as
       nodata. Using an additional alpha channel means that all pixels with an alpha value  of  0
       are transparent. The alpha channel thus represents per-pixel encoding of nodata, just like
       the GRASS MASK (null file). That means when using an alpha channel, you  do  not  need  to
       "free  up" any particular value, but you can use any value you like to replace NULL cells,
       as long as the value can be represented by the Byte data type. It does not matter if  that
       value is already present in any of the input bands.

       Hence for "visual-only" RGB data export it is needed to create an additional alpha channel
       that encodes all NULL cells and in the RGB bands to be 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.

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 or the flags -c and -m.

SEE ALSO

       The GDAL supported formats page.
        r.out.ascii, r.out.bin, r.out.mat, r.out.png, r.out.ppm, r.pack

REFERENCES

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

AUTHORS

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

       Last changed: $Date: 2017-10-12 20:47:34 +0200 (Thu, 12 Oct 2017) $

SOURCE CODE

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

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       © 2003-2018 GRASS Development Team, GRASS GIS 7.4.0 Reference Manual