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m.transform(1grass) GRASS GIS User's Manual m.transform(1grass)


m.transform - Computes a coordinate transformation based on the control points.


miscellaneous, transformation, GCP


m.transform --help
m.transform [-srx] group=name order=integer [format=string[,string,...]] [input=name] [--help] [--verbose] [--quiet] [--ui]


Display summary information

Reverse transform of coords file or coeff. dump
Target east,north coordinates to local x,y

Display transform matrix coefficients

Print usage summary

Verbose module output

Quiet module output

Force launching GUI dialog


Name of input imagery group

Rectification polynomial order
Options: 1-3
Default: 1

Output format
Options: idx, src, dst, fwd, rev, fxy, rxy, fd, rd
Default: fd,rd
idx: point index
src: source coordinates
dst: destination coordinates
fwd: forward coordinates (destination)
rev: reverse coordinates (source)
fxy: forward coordinates difference (destination)
rxy: reverse coordinates difference (source)
fd: forward error (destination)
rd: reverse error (source)

File containing coordinates to transform ("-" to read from stdin)
Local x,y coordinates to target east,north


m.transform is an utility to compute transformation based upon GCPs and output error measurements.

If coordinates are given with the input file option or fed from stdin, both the input and the output format is "x y" with one coordinate pair per line. Reverse transform is performed with the -r flag.

The format option determines how control points are printed out. A summary on the control points can be printed with the -s flag. The summary includes maximum deviation observed when transforming GCPs and overall RMS. The format option is ignored when coordinates are given with the input file option.


The transformations are:


e = [E0 E1][1].[1]
[E2 0][e] [n]
n = [N0 N1][1].[1]
[N2 0][e] [n]

e = [E0 E1 E3][1 ] [1 ]
[E2 E4 0][e ].[n ]
[E5 0 0][e²] [n²]
n = [N0 N1 N3][1 ] [1 ]
[N2 N4 0][e ].[n ]
[N5 0 0][e²] [n²]

e = [E0 E1 E3 E6][1 ] [1 ]
[E2 E4 E7 0][e ].[n ]
[E5 E8 0 0][e²] [n²]
[E9 0 0 0][e³] [n³]
n = [N0 N1 N3 N6][1 ] [1 ]
[N2 N4 N7 0][e ].[n ]
[N5 N8 0 0][e²] [n²]
[N9 0 0 0][e³] [n³]
["." = dot-product, (AE).N = N’EA.]

In other words, order=1 and order=2 are equivalent to order=3 with the higher coefficients equal to zero.


i.rectify, v.rectify, v.transform


Brian J. Buckley
Glynn Clements
Hamish Bowman


Available at: m.transform source code (history)

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© 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual

GRASS 7.8.5