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NAME

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

KEYWORDS

       raster, export, output

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, FITS, XPM, BMP, PCIDSK,
           PCRaster, ILWIS, SGI, SRTMHGT, Leveller, Terragen, GMT, netCDF, HDF4Image, ISIS3, ISIS2,  PDS4,  ERS,
           JP2OpenJPEG,  FIT,  GRIB,  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, RRASTER, BYN, ARG, USGSDEM, BAG, NWT_GRD, ADRG, BLX, EPSILON, PostGISRaster, SAGA, XYZ,
           HF2, JPEGLS, ZMap, SIGDEM, GPKG, NGW, ENVI, EHdr, ISCE
           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).

   Adding overviews to speed up map display in other software
       Adding overviews with gdaladdo after exporting can speed up display. The overviews are created internally
       within  the  exported file. The amount of levels (power-of-two factors) are controlled with the overviews
       parameter. The higher the overview level defined by the user the more lower resolution internal overviews
       are added Note that other software might create their own overviews, ignoring existing overviews.

   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.

       Classic  TIFF  format  supports only files with up to 4GB. Files that exceed this limit (in compressed or
       uncompressed form) need to be exported with createopt="BIGTIFF=YES". BIGTIFF  is  available  if  GDAL  is
       built with libtiff >= 4.0.

   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").

       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 a large raster map in LZW compressed (Big) GeoTIFF format
       g.region raster=elevation -p
       # Using PREDICTOR 2 or 3 (the latter mainly for floating point data) can further reduce file size
       r.out.gdal in=elevation output=elevation.tif createopt="COMPRESS=LZW,PREDICTOR=3,BIGTIFF=YES"

   Export a raster map with internal overview in "Deflate" compressed GeoTIFF format
       g.region raster=elevation -p
       # overviews=5 corresponds to ’gdaladdo ... 2 4 8 16 32’
       r.out.gdal in=elevation output=elevation.tif createopt="COMPRESS=DEFLATE" overviews=5

   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)

SOURCE CODE

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

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual