Ubuntu Manpage: g.proj - Prints or modifies GRASS projection information files (in various co-ordinate system

NAME

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

KEYWORDS

       general, projection, create project

SYNOPSIS

       g.proj
       g.proj --help
       g.proj  [-pgdjfwetc]    [georef=file]     [wkt=file]     [srid=params]     [proj4=params]     [epsg=code]
       [list_codes=string]     [datum=name]     [datum_trans=index]     [project=name]    [--help]   [--verbose]
       [--quiet]  [--ui]

   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-ordinate system

       -c
           Modify current project’s projection files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   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

       srid=params
           Spatial reference ID with authority name and code
           E.g. EPSG:4326 or urn:ogc:def:crs:EPSG::4326

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

       epsg=code
           EPSG projection code
           Options: 1-1000000

       list_codes=string
           List codes for given authority, e.g. EPSG, and exit
           Options: EPSG, ESRI, IAU_2015, IGNF, NKG, NRCAN, OGC, PROJ

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

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

       project=name
           Name of new project (location) to create

DESCRIPTION

g.proj provides a means of converting a coordinate reference system (CRS) description between various
formats.

For an introduction to map projections (with PROJ),see the manual page of r.proj.

If compiled without OGR present, the functionality is limited to:

• Reporting the CRS information for the current project (previously called location), either in
conventional GRASS (-p flag) or PROJ (-j flag) format

• Changing the datum, or reporting and modifying the datum transformation parameters, for the
current project

When compiled with OGR, functionality is increased and allows output of the CRS 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 being read from the current project, the CRS
information is imported from an external source as follows:

georef=filename
g.proj attempts to invoke GDAL and OGR in turn to read a georeferenced file filename. The CRS
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 CRS 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 CRS description in PROJ format, enclosed in quotation marks if there are any
spaces. If - is given for description, the PROJ 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 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
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 CRS 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 CRS files (PROJ_INFO,
PROJ_UNITS, WIND and DEFAULT_WIND) based on the imported information. If the project parameter is
specified in addition to -c, then a new project will be created. Otherwise the CRS information files in
the current project 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.

NOTES

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 exit.
0 (default): Continue without specifying parameters - if used when creating a project, 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 project.

Output is simply based on the input CRS 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 CRS descriptions is limited to 8000 bytes.

EXAMPLES

   Print information
       Print the CRS information for the current project:
       g.proj -p

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

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

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

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

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

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

       Create  a  new  project with the coordinate 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 project=irish_grid

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

       Create a new project with the coordinate system from a WKT definition stored in a text file:
       g.proj -c wkt=irish_grid.prj project=irish_grid

       Create  a  new project from a PROJ description, explicitly specifying a datum and using the default datum
       transformation parameters:
       g.proj -c project=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 project (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 project using the OGR ’ogr2ogr’ tool:
       ogr2ogr -t_srs "`g.proj -wf`" polbnda_italy_GB_ovest.shp polbnda_italy_LL.shp

REFERENCES

       PROJ: 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 (PROJ)

AUTHOR

       Paul Kelly

SOURCE CODE

       Available at: g.proj source code (history)

       Accessed: Thursday Aug 01 11:29:46 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.4.0 Reference Manual