m.transform(1)

💖 m.transform — the GRASS GIS bestie coordinate glow-up 💖

okay so this is m.transform(1), straight out of the GRASS GIS User's Manual (8.4.2, she's current ✨). Sit down, hydrate, because we're computing a coordinate transformation based on the control points and honestly? it's giving main character.

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🌸 NAME 🌸

m.transform — computes a coordinate transformation based on the control points. no cap, that's the whole job. 💅

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🎀 KEYWORDS 🎀

miscellaneous, transformation, GCP

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✨ 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. slay, give me the tea ☕
• -r — Reverse transform of coords file or coeff. dump. Target east,north coordinates to local x,y — so she's going backwards, iconic.
• -x — Display transform matrix coefficients. the math, but visible 👑
• --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. literally required, bestie, don't skip her.
• 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

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💜 DESCRIPTION 💜

m.transform is an utility to compute transformation based upon GCPs and output error measurements. that's it, that's her whole vibe. 🫶

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. periodt.

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. (she said what she said 😭)

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🔥 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. the way that's just math being lazy and honestly valid 💀

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🌟 SEE ALSO 🌟

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

go read those too, bestie, they're the friend group 🦋

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👑 AUTHORS 👑

• Brian J. Buckley
• Glynn Clements
• Hamish Bowman

three icons, no notes 💅

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🍓 SOURCE CODE 🍓

Available at: m.transform source code (history)

Accessed: Saturday Jan 17 05:41:37 2026

Main index | Miscellaneous index | Topics index | Keywords index | Graphical index | Full index

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© 2003-2025 GRASS Development Team, GRASS GIS 8.4.2 Reference Manual

and that's the whole page, bestie — GRASS 8.4.2, m.transform(1), accessed Saturday Jan 17 05:41:37 2026 🧚✨ love u, go transform something 💖