Provided by: grass-doc_6.4.3-3_all bug


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


       general, projection


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

           Create new projection files (modifies current location)

           Verbose module output

           Quiet module output

           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 the projection information for the current location:

       g.proj -p

       Create a '.prj' file in ESRI format corresponding to the current location:

       g.proj -wef > irish_grid.prj

       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 a new location with the co-ordinate system referred to by EPSG code 4326 (Latitude-
       Longitude/WGS84), without explicitly specifiying 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 loc=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:

       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

       List the possible datum transformation parameters for the current location:

       g.proj -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

       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)




       Paul Kelly

       Last changed: $Date: 2012-10-17 13:15:48 -0700 (Wed, 17 Oct 2012) $

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