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m.transform(1grass)

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

NAME

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

KEYWORDS

miscellaneous, transformation, GCP

SYNOPSIS

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

Flags:

-s

Display summary information
-r

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

Display transform matrix coefficients
--help

Print usage summary
--verbose

Verbose module output
--quiet

Quiet module output
--ui

Force launching GUI dialog

Parameters:

group=name [required]

Name of input imagery group
order=integer [required]

Rectification polynomial order
Options: 1-3
Default: 1
format=string[,string,...]

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)
input=name

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

DESCRIPTION

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.

NOTES

The transformations are:

order=1: 



    e = [E0 E1][1]·[1]


        [E2  0][e] [n]


    n = [N0 N1][1]·[1]


        [N2  0][e] [n]
order=2: 


    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]
order=3: 


    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.

SEE ALSO

i.ortho.transform, i.rectify, v.rectify, v.transform

AUTHORS

Brian J. Buckley
Glynn Clements
Hamish Bowman

SOURCE CODE

Available at: m.transform source code (history)

Accessed: Thursday Jun 18 12:49:57 2026

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GRASS 8.5.0