Momocs (version 0.2-03)

tfourier.shape: Calculates and draw "tfourier" shapes.

Description

tfourier.shape calculates a "Fourier tangent angle shape" given Fourier coefficients (see Details) or can generate some "tfourier" shapes.

Usage

tfourier.shape(an, bn, ao = 0, nb.h, nb.pts=80, alpha=2, plot=TRUE)

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.

ao

ao Harmonic coefficient.

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.

Value

• A list with components:
• x
  vector of x-coordinates.
• y
  vector of y-coordinates.

Details

tfourier.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 tfourier for the mathematical background.

References

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

See Also

tfourier.i.

Examples

data(bot)
tf <- tfourier(bot@coo[[1]], 24)
tfourier.shape(tf$an, tf$bn) # equivalent to rfourier.i(rf)
tfourier.shape()
tfourier.shape(nb.h=6, alpha=0.4, nb.pts=500)
panel(Coo(replicate(100, coo.force2close(l2m(tfourier.shape(nb.h=6, alpha=2, nb.pts=200, plot=FALSE)))))) # biological shapes