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       g.proj   -  Prints  or modifies GRASS projection information files (in various co-ordinate
       system descriptions).
       Can also be used to create new GRASS locations.


       general, projection, create location


       g.proj --help
       g.proj   [-pgdjfwetc]    [georef=file]     [wkt=file]      [proj4=params]      [epsg=code]
       [datum=name]    [datum_trans=index]    [location=name]    [--help]  [--verbose]  [--quiet]

           Print projection information in conventional GRASS format

           Print projection information in shell script style

           Verify datum information and print transformation parameters

           Print projection information in PROJ.4 format

           Print ’flat’ output with no linebreaks (applies to WKT and PROJ.4 output)

           Print projection information in WKT format

           Use ESRI-style format (applies to WKT output only)

           Force override of datum transformation information in input co-ordinate system

           Modify current location projection files

           Print usage summary

           Verbose module output

           Quiet module output

           Force launching GUI dialog

           Name of georeferenced data file to read projection information from

           Name of ASCII file containing a WKT projection description
           ’-’ for standard input

           PROJ.4 projection description
           ’-’ for standard input

           EPSG projection code
           Options: 1-1000000

           Datum (overrides any datum specified in input co-ordinate system)
           Accepts standard GRASS datum codes, or "list" to list and exit

           Index number of datum transform parameters
           "0" for unspecified or "-1" to list and exit
           Options: -1-100
           Default: 0

           Name of new location to create


       g.proj provides a means of converting a co-ordinate system  description  (i.e.  projection
       information)  between various formats.  If compiled without OGR present, the functionality
       is limited to:

           ·   Reporting  the  projection  information  for  the  current  location,  either   in
               conventional GRASS (-p flag) or PROJ.4 (-j flag) format

           ·   Changing   the   datum,  or  reporting  and  modifying  the  datum  transformation
               parameters, for the current location

       When compiled with OGR, functionality is increased and allows  output  of  the  projection
       information  in  the  Well-Known  Text  (WKT)  format  popularised  by proprietary GIS. In
       addition, if one of the parameters georef, wkt, proj4 or epsg is  specified,  rather  than
       the  projection  information  being  read from the current location it is imported from an
       external source as follows:

           g.proj attempts to invoke GDAL and OGR in turn to read a georeferenced file  filename.
           The  projection  information  will  be  read  from  this  file.  If  the  file  is not
           georeferenced or cannot be read, XY (unprojected) will be used.

       wkt=filename or -
           The file filename should contain a  projection  description  in  WKT  format  with  or
           without  line-breaks  (e.g.  a  ’.prj’  file). If - is given for the filename, the WKT
           description will be read from stdin rather than a file.

       proj4=description or -
           description should be a projection description in PROJ.4 format, enclosed in quotation
           marks  if  there are any spaces. If - is given for description, the PROJ.4 description
           will be read from stdin rather than as a directly-supplied command-line parameter.

           number should correspond to the index number of a valid co-ordinate system in the EPSG
           database.  EPSG  code  support  is based upon a local copy of the GDAL CSV co-ordinate
           system and datum information files, stored in the directory $GISBASE/etc/proj/ogr_csv.
           These can be updated if necessary to support future revisions of the EPSG database.

       If  datum  information  is incorrect or missing in the input co-ordinate system definition
       (e.g. PROJ.4 descriptions have very limited support for specifying datum names),  a  GRASS
       datum  abbreviation  can instead be supplied using the datum parameter. This will override
       any datum contained in the input co-ordinate system, and discard any datum  transformation
       parameters.  Enter datum=list to return a list of all the datums supported by GRASS. Since
       any existing datum transformation parameters will  have  been  discarded,  the  datumtrans
       parameter should in general always be used in conjunction with datum.

       The  -p,  -j, -w, etc. flags are all functional when importing projection information from
       an external source, meaning that g.proj can be used to convert between representations  of
       the information. It is not required that either the input or output be in GRASS format.

       In  addition however, if the -c flag is specified, g.proj will create new GRASS projection
       files (PROJ_INFO, PROJ_UNITS, WIND and DEFAULT_WIND) based on the imported information. If
       the  location  parameter  is  specified  in  addition  to  -c, then a new location will be
       created.  Otherwise the projection information files  in  the  current  location  will  be
       overwritten. The program will not warn before doing this.

       The  final  mode  of  operation  of g.proj is to report on the datum information and datum
       transformation parameters associated with the co-ordinate system. The -d flag will  report
       a human-readable summary of this.


       If  the  input  co-ordinate system contains a datum name but no transformation parameters,
       and there is more than one suitable  parameter  set  available  (according  to  the  files
       datum.table and datumtransform.table in $GISBASE/etc/proj), g.proj will check the value of
       the datumtrans option and act according to the following:
       -1: List available parameter sets in a GUI-parsable (but also human-readable)  format  and
       0  (default):  Continue  without specifying parameters - if used when creating a location,
       other GRASS modules will use the "default" (likely non-optimum) parameters for this  datum
       if necessary in the future.
       Any  other  number  less  than or equal to the number of parameter sets available for this
       datum: Choose this parameter set and add it to the co-ordinate system description.
       If the -t flag is specified, the module will attempt to change  the  datum  transformation
       parameters  using  one  of  the above two methods even if a valid parameter set is already
       specified in the input co-ordinate  system.  This  can  be  useful  to  change  the  datum
       information for an existing location.

       Output  is  simply  based  on the input projection information. g.proj does not attempt to
       verify that the co-ordinate system thus described matches an existing system in use in the
       world. In particular, this means there are no EPSG Authority codes in the WKT output.

       WKT  format  shows  the  false  eastings and northings in the projected unit (e.g. meters,
       feet) but in PROJ format it should always be given in meters.

       The maximum size of input WKT or PROJ.4 projection descriptions is limited to 8000 bytes.


   Print information
       Print the projection information for the current location:
       g.proj -p

       List the possible datum transformation parameters for the current location:
       g.proj -t datumtrans=-1

   Create projection (PRJ) file
       Create a ’.prj’ file in ESRI format corresponding to the current location:
       g.proj -wef > irish_grid.prj

   Read projection from file
       Read the projection information from a GeoTIFF file and print it in PROJ.4 format:
       g.proj -jf georef=ASTER_DEM20020508161837.tif

       Convert the PROJ.4 projection description contained in a text file to WKT format:
       cat proj4.description | g.proj -w proj4=-

   Create new location
       Create a new  location  with  the  co-ordinate  system  referred  to  by  EPSG  code  4326
       (Latitude-Longitude/WGS84), without explicitly specifying datum transformation parameters:
       g.proj -c epsg=4326 location=latlong

       Create  a  new  location  with the co-ordinate system referred to by ESRI-EPSG code 900913
       (Google Mercator Projection)
       g.proj -c epsg=900913 location=google

       Create a new location with the co-ordinate system referred to by EPSG  code  29900  (Irish
       Grid), selecting datum transformation parameter set no. 2:
       # list available datums for EPSG code 29900
       g.proj -t datumtrans=-1 epsg=29900
       g.proj -c epsg=29900 datumtrans=2 location=irish_grid

       Create  a  new  location  with  the  same  co-ordinate system as the current location, but
       forcing a change to datum transformation parameter set no. 1:
       g.proj -c location=newloc -t datumtrans=1

       Create a new location with the co-ordinate system from a WKT definition stored in  a  text
       g.proj -c wkt=irish_grid.prj location=irish_grid

       Create  a  new location from a PROJ.4 description, explicitly specifying a datum and using
       the default datum transformation parameters:
       g.proj -c location=spain proj4="+proj=utm +zone=30 +ellps=intl" datum=eur50 datumtrans=0

   Using g.proj output for GDAL/OGR tools
       Reproject external raster map to current GRASS projection (does not  always  make  sense!)
       using  the  GDAL  ’gdalwarp’ tool. We recommend to use the ERDAS/Img format and not to use
       the ESRI style of WKT:
       # example for 30x30 pixel resolution (enforce with -tr to avoid odd values)
       gdalwarp -of HFA -tr 30 30 -t_srs "`g.proj -wf`" aster.img aster_tmerc.img

       Reproject external vector map to current GRASS projection using the OGR ’ogr2ogr’ tool:
       ogr2ogr -t_srs "`g.proj -wf`" polbnda_italy_GB_ovest.shp polbnda_italy_LL.shp


       PROJ 4: Projection/datum support library
       GDAL raster library and toolset
       OGR vector library and toolset

       Further reading

           ·   ASPRS Grids and Datum

           ·   MapRef - The Collection of Map Projections and Reference Systems for Europe

           ·   Projections Transform List (PROJ4)


        m.proj, r.proj, v.proj, r.import,, v.import,


       Paul Kelly

       Last changed: $Date: 2016-05-28 08:54:25 +0200 (Sat, 28 May 2016) $


       Available at: g.proj source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual