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)

Reproject vector point coordinate pairs to Long/Lat WGS84¶

The m.proj module is designed to work seamlessly with point data exported 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 CRS using the -i flag which sets the target projection parameters automatically from the current project 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 coordinate list to the target projection.

Datum conversions are automatically handled by the PROJ library if +datum settings 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

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 ellipsoid).

For more usage examples, see the documentation for the PROJ cs2cs program.