Flags:¶

-3

Perform 3D transformation

-o

Perform orthogonal 3D transformation

-r

Print RMS errors
Print RMS errors and exit without rectifying the input map

-b

Do not build topology
Advantageous when handling a large number of points

--overwrite

Allow output files to overwrite existing files

--help

Print usage summary

--verbose

Verbose module output

--quiet

Quiet module output

--ui

Force launching GUI dialog

Parameters:¶

input=name [required]

Name of input vector map
Or data source for direct OGR access

output=name [required]

Name for output vector map

group=name

Name of input imagery group

points=name

Name of input file with control points

rmsfile=name

Name of output file with RMS errors (if omitted or ’-’ output to stdout

order=integer

Rectification polynomial order (1-3)
Options: 1-3
Default: 1

separator=character

Field separator for RMS report
Special characters: pipe, comma, space, tab, newline
Default: pipe

Coordinate transformation and RMSE¶

The desired order of transformation (1, 2, or 3) is selected with the order option. v.rectify will calculate the RMSE if the -r flag is given and print out statistcs in tabular format. The last row gives a summary with the first column holding the number of active points, followed by average deviations for each dimension and both forward and backward transformation and finally forward and backward overall RMSE.

2D linear affine transformation (1st order transformation)¶

x’ = a1 + b1 * x + c1 * y
y’ = a2 + b2 * x + c2 * y

3D linear affine transformation (1st order transformation)¶

x’ = a1 + b1 * x + c1 * y + d1 * z
y’ = a2 + b2 * x + c2 * y + d2 * z
z’ = a3 + b3 * x + c3 * y + d3 * z The a,b,c,d coefficients are determined by least squares regression based on the control points entered. This transformation applies scaling, translation and rotation. It is NOT a general purpose rubber-sheeting, nor is it ortho-photo rectification using a DEM, not second order polynomial, etc. It can be used if (1) you have geometrically correct data, and (2) the terrain or camera distortion effect can be ignored.

Polynomial Transformation Matrix (2nd, 3d order transformation)¶

v.rectify uses a first, second, or third order transformation matrix to calculate the registration coefficients. The minimum number of control points required for a 2D transformation of the selected order (represented by n) is
((n + 1) * (n + 2) / 2) or 3, 6, and 10 respectively. For a 3D transformation of first, second, or third order, the minimum number of required control points is 4, 10, and 20, respectively. It is strongly recommended that more than the minimum number of points be identified to allow for an overly-determined transformation calculation which will generate the Root Mean Square (RMS) error values for each included point. The polynomial equations are determined using a modified Gaussian elimination method.