.TH g.proj 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBg.proj\fR\fR  \- Prints or modifies GRASS projection information files (in various co\-ordinate system descriptions).
.br
Can also be used to create new GRASS locations.
.SH KEYWORDS
general, projection, create location
.SH SYNOPSIS
\fBg.proj\fR
.br
\fBg.proj \-\-help\fR
.br
\fBg.proj\fR [\-\fBpgdjfwetc\fR]  [\fBgeoref\fR=\fIfile\fR]   [\fBwkt\fR=\fIfile\fR]   [\fBproj4\fR=\fIparams\fR]   [\fBepsg\fR=\fIcode\fR]   [\fBlist_codes\fR=\fIstring\fR]   [\fBdatum\fR=\fIname\fR]   [\fBdatum_trans\fR=\fIindex\fR]   [\fBlocation\fR=\fIname\fR]   [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-p\fR" 4m
.br
Print projection information in conventional GRASS format
.IP "\fB\-g\fR" 4m
.br
Print projection information in shell script style
.IP "\fB\-d\fR" 4m
.br
Verify datum information and print transformation parameters
.IP "\fB\-j\fR" 4m
.br
Print projection information in PROJ.4 format
.IP "\fB\-f\fR" 4m
.br
Print \(cqflat\(cq output with no linebreaks (applies to WKT and PROJ.4 output)
.IP "\fB\-w\fR" 4m
.br
Print projection information in WKT format
.IP "\fB\-e\fR" 4m
.br
Use ESRI\-style format (applies to WKT output only)
.IP "\fB\-t\fR" 4m
.br
Force override of datum transformation information in input co\-ordinate system
.IP "\fB\-c\fR" 4m
.br
Modify current location projection files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBgeoref\fR=\fIfile\fR" 4m
.br
Name of georeferenced data file to read projection information from
.IP "\fBwkt\fR=\fIfile\fR" 4m
.br
Name of ASCII file containing a WKT projection description
.br
\(cq\-\(cq for standard input
.IP "\fBproj4\fR=\fIparams\fR" 4m
.br
PROJ.4 projection description
.br
\(cq\-\(cq for standard input
.IP "\fBepsg\fR=\fIcode\fR" 4m
.br
EPSG projection code
.br
Options: \fI1\-1000000\fR
.IP "\fBlist_codes\fR=\fIstring\fR" 4m
.br
List codes for given authority, e.g. EPSG, and exit
.br
Options: \fIEPSG, ESRI, IGNF, NKG, OGC, PROJ\fR
.IP "\fBdatum\fR=\fIname\fR" 4m
.br
Datum (overrides any datum specified in input co\-ordinate system)
.br
Accepts standard GRASS datum codes, or \(dqlist\(dq to list and exit
.IP "\fBdatum_trans\fR=\fIindex\fR" 4m
.br
Index number of datum transform parameters
.br
\(dq0\(dq for unspecified or \(dq\-1\(dq to list and exit
.br
Options: \fI\-1\-100\fR
.br
Default: \fI0\fR
.IP "\fBlocation\fR=\fIname\fR" 4m
.br
Name of new location to create
.SH DESCRIPTION
.PP
\fIg.proj\fR 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:
.RS 4n
.IP \(bu 4n
Reporting the projection information for the current location,
either in conventional GRASS (\-p flag) or PROJ (\-j flag) format
.IP \(bu 4n
Changing the datum, or reporting and modifying the datum transformation
parameters, for the current location
.RE
.PP
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 \fIgeoref\fR,
\fIwkt\fR, \fIproj4\fR or \fIepsg\fR is specified, rather than the
projection information being read from the current location it is imported
from an external source as follows:
.IP "georef=\fIfilename\fR" 4m
.br
\fIg.proj\fR attempts to invoke GDAL and OGR in turn to read a
georeferenced file \fIfilename\fR. The projection information will be
read from this file. If the file is not georeferenced or cannot be read,
XY (unprojected) will be used.
.IP "wkt=\fIfilename\fR or \fI\-\fR" 4m
.br
The file \fIfilename\fR should contain a projection description in WKT
format with or without line\-breaks (e.g. a \(cq.prj\(cq file). If \fI\-\fR is given
for the filename, the WKT description will be read from stdin rather than a
file.
.IP "proj4=\fIdescription\fR or \fI\-\fR" 4m
.br
\fIdescription\fR should be a projection description in
PROJ format, enclosed in
quotation marks if there are any spaces. If \fI\-\fR is given for
\fIdescription\fR, the PROJ description will be read from stdin rather
than as a directly\-supplied command\-line parameter.
.IP "epsg=\fInumber\fR" 4m
.br
\fInumber\fR 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.
.PP
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 \fIdatum\fR parameter. This will override any
datum contained in the input co\-ordinate system, and discard
any datum transformation parameters. Enter datum=\fIlist\fR to return a
list of all the datums supported by GRASS. Since any
existing datum transformation parameters will have been discarded, the
\fIdatumtrans\fR parameter should in general always be used in
conjunction with \fIdatum\fR.
.PP
The \-p, \-j, \-w, etc. flags are all functional when importing projection
information from an external source, meaning that \fIg.proj\fR can be
used to convert between representations of the information. It is
not required that either the input or output be in GRASS
format.
.PP
In addition however, if the \-c flag is specified, \fIg.proj\fR will
create new GRASS projection files (PROJ_INFO, PROJ_UNITS, WIND and
DEFAULT_WIND) based on the imported information. If the \fIlocation\fR
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.
.PP
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.
.SH NOTES
.PP
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), \fIg.proj\fR will check the value of
the \fIdatumtrans\fR option and act according to the following:
.br
\-1: List available parameter sets in a GUI\-parsable (but also
human\-readable) format and exit.
.br
0 (default): Continue without specifying parameters \- if
used when creating a location, other GRASS modules will use the \(dqdefault\(dq
(likely non\-optimum) parameters for this datum if necessary in the future.
.br
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.
.br
If the \fI\-t\fR 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.
.PP
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.
.PP
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.
.PP
The maximum size of input WKT or PROJ projection descriptions is
limited to 8000 bytes.
.SH EXAMPLES
.SS Print information
Print the projection information for the current location:
.br
.br
.nf
\fC
g.proj \-p
\fR
.fi
.PP
List the possible datum transformation parameters for the current location:
.br
.br
.nf
\fC
g.proj \-t datumtrans=\-1
\fR
.fi
.SS Create projection (PRJ) file
Create a \(cq.prj\(cq file in ESRI format corresponding to the current location:
.br
.br
.nf
\fC
g.proj \-wef > irish_grid.prj
\fR
.fi
.SS Read projection from file
Read the projection information from a GeoTIFF file and print it in PROJ
format:
.br
.br
.nf
\fC
g.proj \-jf georef=ASTER_DEM20020508161837.tif
\fR
.fi
.PP
Convert the PROJ projection description contained in a text file to WKT
format:
.br
.br
.nf
\fC
cat proj4.description | g.proj \-w proj4=\-
\fR
.fi
.SS Create new location
.PP
Create a new location with the co\-ordinate system referred to by EPSG code
4326 (Latitude\-Longitude/WGS84), without explicitly specifying datum
transformation parameters:
.br
.br
.nf
\fC
g.proj \-c epsg=4326 location=latlong
\fR
.fi
.PP
Create a new location with the co\-ordinate system referred to by ESRI\-EPSG code
900913 (Google Mercator Projection)
.br
.br
.nf
\fC
g.proj \-c epsg=900913 location=google
\fR
.fi
.PP
Create a new location with the co\-ordinate system referred to by EPSG code
29900 (Irish Grid), selecting datum transformation parameter set no. 2:
.br
.br
.nf
\fC
# list available datums for EPSG code 29900
g.proj \-t datumtrans=\-1 epsg=29900
g.proj \-c epsg=29900 datumtrans=2 location=irish_grid
\fR
.fi
.PP
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:
.br
.br
.nf
\fC
g.proj \-c location=newloc \-t datumtrans=1
\fR
.fi
.PP
Create a new location with the co\-ordinate system from a WKT definition
stored in a text file:
.br
.br
.nf
\fC
g.proj \-c wkt=irish_grid.prj location=irish_grid
\fR
.fi
.PP
Create a new location from a PROJ description, explicitly
specifying a datum and using the default datum transformation
parameters:
.br
.br
.nf
\fC
g.proj \-c location=spain proj4=\(dq+proj=utm +zone=30 +ellps=intl\(dq datum=eur50 datumtrans=0
\fR
.fi
.SS Using g.proj output for GDAL/OGR tools
.PP
Reproject external raster map to current GRASS projection (does not always make sense!)
using the GDAL \(cqgdalwarp\(cq tool. We recommend to use the ERDAS/Img format and not
to use the ESRI style of WKT:
.br
.br
.nf
\fC
# example for 30x30 pixel resolution (enforce with \-tr to avoid odd values)
gdalwarp \-of HFA \-tr 30 30 \-t_srs \(dq\(gag.proj \-wf\(ga\(dq aster.img aster_tmerc.img
\fR
.fi
.PP
Reproject external vector map to current GRASS projection
using the OGR \(cqogr2ogr\(cq tool:
.br
.br
.nf
\fC
ogr2ogr \-t_srs \(dq\(gag.proj \-wf\(ga\(dq polbnda_italy_GB_ovest.shp polbnda_italy_LL.shp
\fR
.fi
.SH REFERENCES
PROJ: Projection/datum support library
.br
GDAL raster library and toolset
.br
OGR vector library and toolset
.PP
\fBFurther reading\fR
.RS 4n
.IP \(bu 4n
ASPRS Grids and Datum
.IP \(bu 4n
MapRef \- The Collection of Map Projections and Reference Systems for Europe
.IP \(bu 4n
Projections Transform List (PROJ)
.RE
.SH SEE ALSO
\fI
m.proj,
r.proj,
v.proj,
r.import,
r.in.gdal,
v.import,
v.in.ogr
\fR
.SH AUTHOR
Paul Kelly
.SH SOURCE CODE
.PP
Available at: g.proj source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual