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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.

SEE ALSO

i.rectify

AUTHORS

Brian J. Buckley
Glynn Clements
Hamish Bowman

Last changed: $Date: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $


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