# sfourier_i: Inverse radii variation Fourier transform In Momocs: Morphometrics using R

## Description

`sfourier_i` uses the inverse radii variation (equally spaced curvilinear abscissa) transformation to calculate a shape, when given a list with Fourier coefficients, typically obtained computed with sfourier.

## Usage

 `1` ```sfourier_i(rf, nb.h, nb.pts = 120, dtheta = FALSE) ```

## Arguments

 `rf` A `list` with `ao`, `an` and `bn` components, typically as returned by `sfourier`. `nb.h` `integer`. The number of harmonics to calculate/use. `nb.pts` `integer`. The number of points to calculate. `dtheta` `logical`. Whether to use the dtheta correction method. `FALSE` by default. When `TRUE`, tries to correct the angular difference between reconstructed points; otherwise equal angles are used.

## Value

A list with components:

 `x ` `vector` of `x`-coordinates. `y ` `vector` of `y`-coordinates. `angle` `vector` of angles used. `r` `vector` of radii calculated.

## References

Renaud S, Pale JRM, Michaux JR (2003): Adaptive latitudinal trends in the mandible shape of Apodemus wood mice. J Biogeogr 30:1617-1628.

Other sfourier: `sfourier_shape`, `sfourier`
 ```1 2 3 4 5 6``` ```coo <- coo_center(bot[1]) # centering is almost mandatory for sfourier family coo_plot(coo) rf <- sfourier(coo, 12) rf rfi <- sfourier_i(rf) coo_draw(rfi, border='red', col=NA) ```