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# Control Points [0.8.1 and later]

Control points are used for 2D and 3D alignment, and to constrain 3D scene models. Control point data is loaded from a control point file. Scripts to generate and manipulate control point files are included in the `scripts` directory of the source distribution; the file specification is outlined in the final section below.

## Loading a Control Point File

The --cpf-load= option is used to load data from a control point file.

    --cpf-load=<f>    Load control point data from file <f>   [0.8.1 and later]

## Control Point File Format (version 0)

The version 0 control point file format consists of a version command followed by a sequence of control points, with one control point per line of the file.

    V 0
    Control Point 1
    Control Point 2
    Control Point 3
    .
    .
    .

Control points can be one of three types:

### Type A control points

Type A control points specify a sequence of 2D points, one for each frame, where each point is specified as a pair of floating point numbers. If there is no data for a frame, then "nan" should be specified. E.g.:

    A 20  30  nan nan 10  10  10  15
    A 23  22  25  25  nan nan nan nan

### Type B control points

Type B control points specify a 3D coordinate. E.g.:

    B 10 30 -400
    B 10 15 -425

### Type C control points

Type C control points specify both 2D and 3D data. There is a single 3D point specified, as well as one 2D point for each frame. The 3D point appears at the end of the line. E.g.:

    C 20  30  nan nan 10  10  10  15  10 30 -400
    C 23  22  25  25  nan nan nan nan 10 15 -425

Copyright 2005 David Hilvert

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