m.proj(1grass) GRASS GIS User's Manual m.proj(1grass)
NAME
m.proj - Converts coordinates from one projection to another (cs2cs
frontend).
KEYWORDS
miscellaneous, projection, transformation
SYNOPSIS
m.proj
m.proj --help
m.proj [-iodec] [coordinates=east,north] [input=name] [out-
put=name] [separator=character] [proj_in=string]
[proj_out=string] [--overwrite] [--help] [--verbose] [--quiet]
[--ui]
Flags:
-i
Use LL WGS84 as input and current location as output projection
-o
Use current location as input and LL WGS84 as output projection
-d
Output long/lat in decimal degrees, or other projections with many
decimal places
-e
Include input coordinates in output file
-c
Include column names in output file
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
coordinates=east,north
Input coordinates to reproject
input=name
Name of input coordinate file
’-’ for standard input
output=name
Name for output coordinate file (omit to send to stdout)
separator=character
Field separator (format: input[,output])
Special characters: pipe, comma, space, tab, newline
Default: pipe
proj_in=string
Input projection parameters (PROJ.4 style)
proj_out=string
Output projection parameters (PROJ.4 style)
DESCRIPTION
This program allows a user to convert coordinates from one projection
to another. Coordinates can be read from one file, converted, and re-
sults written to another file. Alternatively, if the input=-, eastings
and northings may be passed to the program directly from standard in-
put. If the output option is omitted, the results are sent directly to
standard output. In this way m.proj can be used as a simple frontend to
the PROJ cs2cs utility. The -i or -o flags make the task especially
easy for the common problem of converting to or from lat/long WGS84.
Note: This program does not transform GRASS maps, it is designed to de-
termine the equivalent coordinate values of an individual position or
list of positions. Use v.proj to reproject vector maps or r.proj for
raster maps.
For an introduction to map projections (with PROJ),see the manual page
of r.proj.
NOTES
cs2cs expects input data to formatted as x y, so if working with lati-
tude-longitude data be sure to send the x value first, i.e., longi-
tude latitude. Output data will be exported using the same convention.
cs2cs will treat a third data column as a z value (elevation) and will
modify the value accordingly. This usually translates into small but
real differences in that data column.
cs2cs does not expect the input stream to contain column headings, only
numbers. If your data file has lines you wish to have passed through
without being processed, they must start with the ’#’ character.
If sending m.proj data from standard input, be aware that the data is
first stored to a temporary file before being processed with cs2cs. It
is therefore not advisable to send m.proj data from an open data
stream. The module will stop listening for incoming data after 2 sec-
onds of inactivity. You may use the projection parameters gleaned from
m.proj’s verbose mode (--verbose) with cs2cs directly in this case.
Custom projection parameters can be used via the proj_in and proj_out
options. Full documentation of the projection parameter format may be
found on the PROJ website. Using these options will fully override the
default parameters the module would normally use.
By using the --verbose verbose flag, the user can see exactly what pro-
jection parameters will be used in the conversion as well as some other
informative messages.
If output is to lat/long, it will be formatted using PROJ’s De-
gree:Minute:Second (DMS) convention of DDDdMM’SSS.SS"H. This can be
handy if you wish to quickly convert lat/long decimal degree data into
its DMS equivalent.
Alternatively, to have m.proj output data in decimal degrees, use the
-d flag. This flag can also be used with non-lat/long data to force a
higher number of decimal places (the cs2cs default is 2).
Note that Lat/long output can be converted to GRASS’s DMS convention
(DDD:MM:SSS.SSSH) by piping the results of m.proj through the sed
stream editor as follows.
m.proj -o ... | sed -e ’s/d/:/g’ -e "s/’/:/g" -e ’s/"//g’
EXAMPLES
The examples are suitable for the North Carolina sample dataset if not
stated otherwise:
Reproject vector point coordinate pairs to Long/Lat WGS84
The m.proj module is designed to work seamlessly with point data ex-
ported from the GIS with v.out.ascii, as the following example shows.
# Long/Lat WGS84 output in DMS
v.out.ascii bridges | m.proj -o input=-
# Long/Lat WGS84 output in decimal degree
v.out.ascii bridges | m.proj -o -d input=-
Reproject Long/Lat WGS84 coordinate pair to current map projection
To convert a Long/Lat WGS84 coordinate pair to the current map projec-
tion using the -i flag which sets the target projection parameters au-
tomatically from the current location definition:
echo "-78.61168178 33.92225767" | m.proj -i input=-
645513.47|19180.31|0.00
The same, but load points from a file named waypoints.txt and continue
on to import the results into a GRASS vector points map in the current
map projection:
# check file content
cat waypoints.txt
-78.43977824 33.89587173
-78.54944691 33.88964566
-78.51078074 33.88141495
-77.14037951 35.60543020
# reproject points and generate vector map on the fly
m.proj -i input=waypoints.txt | v.in.ascii input=- output=test_pnts
# verify result
v.db.select test_pnts cat|dbl_1|dbl_2|dbl_3
1|661427.74|16329.14|0
2|651285.43|15586.79|0
3|654867.21|14690.64|0
4|778074.58|207402.6|0
Custom projection parameter usage
To transform points from a UTM projection (here specified with detailed
projection definition rather than using an EPSG code) into the
Gauss-Krüger Grid System, importing from and exporting to files:
m.proj proj_in="+proj=utm +name=utm +a=6378137.0 +es=0.006694380 \
+zone=32 +unfact=1.0" proj_out="+proj=tmerc +name=tmerc \
+a=6377397.155 +es=0.0066743720 +lat_0=0.0 +lon_0=9.0 +k=1.0 \
+x_0=3500000.0" input=utm.coord.txt output=new.gk.coord.txt
Projection parameters provided in the above case: +proj (projection
type), +name (projection name), +a (ellipsoid: equatorial radius), +es
(ellipsoid: eccentricity squared), +zone (zone for the area), +unfact
(conversion factor from meters to other units, e.g. feet), +lat_0
(standard parallel), +lon_0 (central meridian), +k (scale factor) and
+x_0 (false easting). Sometimes false northing is needed which is coded
as +y_0. Internally, the underlying PROJ projection library performs
an inverse projection to latitude-longitude and then projects the coor-
dinate list to the target projection.
Datum conversions are automatically handled by the PROJ library if +da-
tum setings are specified on both the input and output projections on
the command line. The +towgs84 parameter can be used to define either 3
or 7 term datum transform coefficients, satisfying this requirement.
If a datum is specified there is no need for the +ellps= or underlying
parameters, +a=, +es=, etc.
Another custom parameter usage example:
m.proj proj_in="+proj=tmerc +datum=ire65 +lat_0=53.5 +lon_0=-8 +x_0=200000 \
+y_0=250000 +k=1.000035" proj_out="+proj=ll +datum=wgs84" input=wpt.txt
or without datum transformation:
m.proj proj_in="+proj=tmerc +ellps=modif_airy +lat_0=53.5 +lon_0=-8 +x_0=200000 \
+y_0=250000 +k=1.000035" proj_out="+proj=ll +datum=wgs84" input=wpt.txt
In this example no datum transformation will take place as a datum was
not specified for the input projection. The datum specified for the
output projection will thus be silently ignored and may be left out;
all that is achieved a simple conversion from projected to geodetic
co-ordinates, keeping the same datum (and thus also the same ellip-
soid).
For more usage examples, see the documentation for the PROJ cs2cs pro-
gram.
REFERENCES
• Evenden, G.I. (1990) Cartographic projection procedures for
the UNIX environment - a user’s manual. USGS Open-File Report
90-284 (OF90-284.pdf) See also there: Interim Report and 2nd
Interim Report on Release 4, Evenden 1994).
• PROJ Cartographic Projection Library
SEE ALSO
g.proj, r.proj, v.proj, i.rectify, v.in.ascii, v.out.ascii
AUTHOR
M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
Functionality inspired by the m.proj and m.proj2 modules for GRASS GIS
5.
SOURCE CODE
Available at: m.proj source code (history)
Accessed: unknown
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GRASS 7.8.7 m.proj(1grass)
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