MAPPROJECT

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#ifdef SI #define UNIT cm #else #define UNIT inch #endif  

NAME

mapproject - Forward and Inverse map transformation of 2-D coordinates  

SYNOPSIS

mapproject infiles -Jparameters -Rwest/east/south/north[r] [ -C ] [ -F[k|m] ] [ -H ] [ -I ] [ -M[flag] ] [ -S ] [ -V ] [ -: ]  

DESCRIPTION

mapproject reads (longitude, latitude) positions from infiles [or standard input] and computes (x,y) coordinates using the specified map projection and scales. Optionally, it can read (x,y) positions and compute (longitude, latitude) values doing the inverse transformation. This can be used to transform linear (x,y) points obtained by digitizing a map of known projection to geographical coordinates. Additional data fields are permitted after the first 2 columns which must have (longitude,latitude) or (x,y). See option -: on how to read (latitude,longitude) files.
       No space between the option flag and the associated arguments. Use upper case for the
option flags and lower case for modifiers.
infiles
Data file(s) to be transformed. If not given, standard input is read. #include "explain_-J.txt" #include "explain_-R.txt"
 

OPTIONS

infile(s)
input file(s) with 2 or more columns. If no file(s) is given, mapproject will read standard input.
-C
Set center of projected coordinates to be at map projection center [Default is lower left corner].
-F
Force 1:1 scaling, i.e., input data is in actual projected meters. Append k to get projected km, or m to get miles. #include "explain_-H.txt"
-I
Do the Inverse transformation, i.e. get (longitude,latitude) from (x,y) data.
-M
Multiple segment file. Segments are separated by a record whose first character is <flag>. [Default is '>'].
-S
Suppress points that fall outside the region. #include "explain_-V.txt" #include "explain_-t.txt"
 

EXAMPLES

To transform a file with (longitude,latitude) into (x,y) positions in UNIT on a Mercator grid for a given scale, run

mapproject lonlatfile -R20/50/12/25 -Jm0.25 > xyfile

To transform several files with (latitude,longitude) into (x,y) positions in UNIT on a Transverse Mercator grid (central longitude 75W) for scale = 1:500000 and suppress those points that would fall outside the map area, run

mapproject tracks.* -R-80/-70/20/40 -Jt-75/1:500000 -: -S > tmfile.xy
 

RESTRICTIONS

The rectangular input region set with -R will in general be mapped into a non-rectangular grid. Unless -C is set, the leftmost point on this grid has xvalue = 0.0, and the lowermost point will have yvalue = 0.0. Thus, before you digitize a map, run the extreme map coordinates through mapproject using the appropriate scale and see what (x,y) values they are mapped onto. Use these values when setting up for digitizing in order to have the inverse transformation work correctly, or alternatively, use awk to scale and shift the (x,y) values before transforming.  

SEE ALSO

gmtdefaults, gmt, project #include "refs.i"

Snyder, J. P., 1987, Map Projections - A Working Manual, U.S. Geological Survey Prof. Paper 1395.


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
RESTRICTIONS
SEE ALSO

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