Ptolemy {Momocs}

Ptolemaic ellipses and illustration of efourier

Description

Calculate and display Ptolemaic ellipses which illustrates intuitively the principle behing elliptical Fourier analysis.

Usage

Ptolemy(
  coo,
  t = seq(0, 2 * pi, length = 7)[-1],
  nb.h = 3,
  nb.pts = 360,
  palette = col_heat,
  zoom = 5/4,
  legend = TRUE,
  ...
)

Arguments

coo

a matrix of (x; y) coordinates

t

A vector af angles (in radians) on which to display ellipses

nb.h

integer. The number of harmonics to display

nb.pts

integer. The number of points to use to display shapes

palette

a color palette

zoom

numeric a zoom factor for coo_plot

legend

logical. Whether to plot the legend box

...

additional parameters to feed coo_plot

Value

a drawing on the last plot

References

This method has been inspired by the figures found in the followings papers. Kuhl FP, Giardina CR. 1982. Elliptic Fourier features of a closed contour. Computer Graphics and Image Processing 18: 236-258. Crampton JS. 1995. Elliptical Fourier shape analysis of fossil bivalves: some practical considerations. Lethaia 28: 179-186.

See Also

An intuitive explanation of elliptic Fourier analysis can be found in the Details section of the efourier function.

exemplifying functions

Examples

cat <- shapes[4]
Ptolemy(cat, main="An EFT cat")