Momocs (version 1.4.1)

rfourier_shape: Calculates and draw 'rfourier' shapes.

Description

rfourier_shape calculates a 'Fourier radii variation shape' given Fourier coefficients (see Details) or can generate some 'rfourier' shapes.

Usage

rfourier_shape(an, bn, nb.h, nb.pts = 80, alpha = 2, plot = TRUE)

Value

A matrix of (x; y) coordinates.

Arguments

an

numeric. The \(a_n\) Fourier coefficients on which to calculate a shape.

bn

numeric. The \(b_n\) Fourier coefficients on which to calculate a shape.

nb.h

integer. The number of harmonics to use.

nb.pts

integer. The number of points to calculate.

alpha

numeric. The power coefficient associated with the (usually decreasing) amplitude of the Fourier coefficients (see Details).

plot

logical. Whether to plot or not the shape.

Details

rfourier_shape can be used by specifying nb.h and alpha. The coefficients are then sampled in an uniform distribution \((-\pi ; \pi)\) and this amplitude is then divided by \(harmonicrank^alpha\). If alpha is lower than 1, consecutive coefficients will thus increase. See rfourier for the mathematical background.

References

Claude, J. (2008) Morphometrics with R, Use R! series, Springer 316 pp.

See Also

Other rfourier: rfourier_i(), rfourier()

Examples

data(bot)
rf <- rfourier(bot[1], 24)
rfourier_shape(rf$an, rf$bn) # equivalent to rfourier_i(rf)
rfourier_shape() # not very interesting

rfourier_shape(nb.h=12) # better
rfourier_shape(nb.h=6, alpha=0.4, nb.pts=500)

# Butterflies of the vignette' cover
panel(Out(a2l(replicate(100,
rfourier_shape(nb.h=6, alpha=0.4, nb.pts=200, plot=FALSE)))))