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Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

NAME - Generate ground control points for image group to be rectified.


imagery, ground control points

SYNOPSIS --help [-c] group=name source_image=name target_image=name [order=integer] npoints=integer [detail=string] [threshold=float] [--help] [--verbose] [--quiet] [--ui]


Use current region settings in source location instead of source map extends
Print usage summary
Verbose module output
Quiet module output
Force launching GUI dialog


group=name [required]
Name of input imagery group
source_image=name [required]
Name of input raster map
target_image=name [required]
Name of input raster map
Transformation polynom order (1-3)
Options: 1, 2, 3
Default: 1
npoints=integer [required]
Maximum number of points to generate
How detailed should the information be to be used.
Options: coarse, medium, fine
Default: fine
RMS error threshold. Recommended: source image resolution or smaller
Default: 0.0

Table of contents

DESCRIPTION tries to automatically generate a given number of new ground control points (GCPs) by matching the input map to a target map through FFT correlation, based on a few existing ground control points, previously defined by the user, for example through the Ground Control Points Manager. The goal of the module is thus to automaticallty increase the number of control points to enable higher quality geocoding of imagery to a master image (co-registration).


It is recommended to use maps filtered with the DIVERSITY or STDDEV filters of the r.neighbors module, with a window size of 3x3 or 5x5 pixels. However, the algorithm sometimes works well also with the original maps. The produced GCPs can then be used on the original imagery.

The actual number of newly generated ground control points will likely be less than the given maximum number of ground control points because each generated point is filtered using its FFT correlation coefficient, and optionally also by the given RMS threshold. supports the usual transformation orders 1-3 and requires the corresponding number of previously set ground control points: 3 for order 1, 6 for order 2, 10 for order 3.


The GRASS 4 Image Processing manual, i.rectify,, r.neighbors, Ground Control Points Manager


(note that the former module name was i.coregister)


Ivan Michelazzi
Luca Miori
Markus Metz


Available at: source code (history)

Latest change: Monday Jan 30 19:52:26 2023 in commit: cac8d9d848299297977d1315b7e90cc3f7698730

Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

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