GRASS GIS manual: g.transform

NAME

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

KEYWORDS

general, transformation, GCP

SYNOPSIS

g.transform
g.transform help
g.transform [-srx] group=name order=integer [format=string[,string,...]] [coords=name] [--verbose] [--quiet]

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
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

group=name: Name of input imagery group
order=integer: Rectification polynomial order; Options: 1-3
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)
coords=name: File containing coordinates to transform ("-" to read from stdin); Local x,y coordinates to target east,north

DESCRIPTION

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

NOTES

For coordinates given with the coords file option or fed from stdin, the input format is "x y" with one coordinate pair per line.

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.

AUTHORS

Brian J. Buckley
Glynn Clements
Hamish Bowman

Last changed: $Date: 2010-09-18 12:45:32 -0700 (Sat, 18 Sep 2010) $

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