tfourier: Tangent angle Fourier transform

Description

tfourier computes tangent angle Fourier analysis from a matrix or a list of coordinates.

Usage

tfourier(x, ...)
# S3 method for default
tfourier(x, nb.h, smooth.it = 0, norm = FALSE,
  verbose = TRUE, ...)
# S3 method for Out
tfourier(x, nb.h = 40, smooth.it = 0, norm = TRUE,
  verbose = TRUE, ...)

Arguments

A list or matrix of coordinates or an Out

...

useless here

nb.h

integer. The number of harmonics to use. If missing, 12 is used on shapes; 99 percent of harmonic power on Out objects, both with messages.

smooth.it

integer. The number of smoothing iterations to perform

norm

logical. Whether to scale and register new coordinates so that the first point used is sent on the origin.

verbose

logical. Whether to display diagnosis messages.

Value

A list with the following components:

ao ao harmonic coefficient
an vector of \(a_{1->n}\) harmonic coefficients
bn vector of \(b_{1->n}\) harmonic coefficients
phi vector of variation of the tangent angle
t vector of distance along the perimeter expressed in radians
perimeter numeric. The perimeter of the outline
thetao numeric. The first tangent angle
x1 The x-coordinate of the first point
y1 The y-coordinate of the first point.

References

Zahn CT, Roskies RZ. 1972. Fourier Descriptors for Plane Closed Curves. IEEE Transactions on Computers C-21: 269-281. Claude, J. (2008) Morphometrics with R, Use R! series, Springer 316 pp.

Examples

Run this code

data(bot)
coo <- bot[1]
coo_plot(coo)
tf  <- tfourier(coo, 12)
tf
tfi <- tfourier_i(tf)
coo_draw(tfi, border='red', col=NA) # the outline is not closed...
coo_draw(tfourier_i(tf, force2close=TRUE), border='blue', col=NA) # we force it to close.