geomorph (version 1.1-6)

define.sliders.2d: Select points to "slide" along two-dimensional curves.

Description

An interactive function to define which landmarks will "slide" along two-dimensional (2D) curves.

Usage

define.sliders.2d(spec, nsliders)

Arguments

spec

Name of specimen, as an object matrix containing 2D landmark coordinates

nsliders

Number of landmarks to be semilandmarks that slide along curves

Value

• Function returns a 'nsliders-x-3' matrix containing the landmark address of the curve sliders, indicating the landmarks between which the slider landmarks will "slide". The matrix is also written to working directory as "curveslide.csv". Matrix (or "curveslide.csv") is designed for use by gpagen during GPA.

Details

Function takes a matrix of digitized landmark coordinates, such as made by digitize2d, and helps user choose which landmarks will be treated as "curve sliders" in Generalized Procrustes analysis gpagen. This type of semilandmark "slides" along curves lacking known landmarks (see Bookstein 1991:376-382, 1997 for algorithm details). Each sliding semilandmark ("sliders") will slide between two designated points, along a line tangent to the specified curvature. Selection{ Choosing which landmarks will be sliders involves landmark selection using a mouse in the plot window. To define the sliders, for each sliding landmark along the curve in the format 'before-slider-after', using the LEFT mouse button (or regular button for Mac users), click on the hollow circle to choose the landmark in the following order:

1. Click to choose the first landmark between which semi-landmark will "slide",
2. Click to choose sliding landmark,
3. Click to choose the last landmark between which semi-landmark will "slide", Selected landmarks will be filled in and lines are drawn connecting the three landmarks, and will highlight the sliding semilandmark in red and the flanking landmarks in blue.

This procedure is overlapping, so for example, a curve defined by a sequence of semilandmarks, the user must select the 2nd point of the first three to be the 1st for the next e.g. 1 2 3 then 2 3 4, then 3 4 5 etc. }

References

Bookstein, F. J. 1991 Morphometric Tools for Landmark Data: Geometry and Biology. Cambridge University Press, New York. Bookstein, F. J. 1997 Landmark Methods for Forms without Landmarks: Morphometrics of Group Differences in Outline Shape. Medical Image Analysis 1(3):225-243.

See Also

digitize2d, gpagen