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g.proj(1)		      Grass User's Manual		     g.proj(1)

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

KEYWORDS
       general,	projection

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

   Flags:
       -p
	   Print projection information	in conventional	GRASS format

       -g
	   Print projection information	in shell script	style

       -d
	   Verify datum	information and	print transformation parameters

       -j
	   Print projection information	in PROJ.4 format

       -f
	   Print 'flat'	output with no linebreaks (applies to WKT  and	PROJ.4
	   output)

       -w
	   Print projection information	in WKT format

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

       -t
	   Force  override of datum transformation information in input	co-or-
	   dinate system

       -c
	   Create new projection files (modifies current location)

       --verbose
	   Verbose module output

       --quiet
	   Quiet module	output

   Parameters:
       georef=file
	   Name	of georeferenced data file to read projection information from

       wkt=file
	   Name	of ASCII file containing a WKT projection description
	   '-' for standard input

       proj4=params
	   PROJ.4 projection description
	   '-' for standard input

       epsg=code
	   EPSG	projection code
	   Options: 1-1000000

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

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

       location=name
	   Name	of new location	to create

DESCRIPTION
       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  lo-
		     cation,  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	 popu-
       larised	by proprietary GIS. In addition, if one	of the parameters geo-
       ref, wkt, proj4 or epsg is specified, rather than the projection	infor-
       mation  being read from the current location it is imported from	an ex-
       ternal source as	follows:

       georef=filename
	   g.proj attempts to invoke GDAL and OGR in turn to read a  georefer-
	   enced  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.

       epsg=number
	   number should correspond to the index number	of a valid co-ordinate
	   system in the EPSG database.	EPSG code support is based upon	a  lo-
	   cal	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 con-
       tained in the input co-ordinate system, and discard any datum transfor-
       mation  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  DE-
       FAULT_WIND)  based on the imported information. If the location parame-
       ter is specified	in addition to -c, then	a new location	will  be  cre-
       ated.   Otherwise the projection	information files in the current loca-
       tion 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	infor-
       mation and datum	transformation parameters associated with the co-ordi-
       nate system. The	-d flag	will report a human-readable summary of	this.

NOTES
       If the input co-ordinate	system contains	a datum	name but no  transfor-
       mation  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 exit.
       0 (default): Continue without specifying	parameters - if	used when cre-
       ating 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 da-
       tum 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  ex-
       isting 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 me-
       ters.

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

EXAMPLES
       Print the projection information	for the	current	location:

       g.proj -p

       Create  a '.prj'	file in	ESRI format corresponding to the current loca-
       tion:

       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 loca-
       tion:

       g.proj -t datumtrans=-1

       Create a	new location with the co-ordinate system from a	WKT definition
       stored in a text	file:

       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"  da-
       tum=eur50 datumtrans=0

       Reproject external raster map to	current	GRASS projection (does not al-
       ways 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	 polb-
       nda_italy_LL.shp

REFERENCES
       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)

SEE ALSO
       g.setproj
       r.in.gdal
       v.in.ogr

AUTHOR
       Paul Kelly

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

       Full index

       (C) 2003-2016 GRASS Development Team

GRASS 6.4.6							     g.proj(1)

NAME | KEYWORDS | SYNOPSIS | DESCRIPTION | NOTES | EXAMPLES | REFERENCES | SEE ALSO | AUTHOR

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