Identify the inner polygon of a point set

This function identifies the inner polygon of a given set of points. It uses a method of concentric mirroring around a center point, applies an alpha hull to the mirrored shape, and then mirrors the result back.

Usage

inside_polygon(x, y, concavity, center = NULL)

Arguments

x

A numeric vector representing the x coordinates of the points.

y

A numeric vector representing the y coordinates of the points.

concavity

A strictly positive parameter that influences the shape of the inner polygon. Smaller values result in a shape that closely follows the inner boundary, while larger values create a shape that focuses more on the central area.

center

A numeric vector of length 2, representing the (x,y) coordinates of the center point for the mirroring process. If NULL, the mid-ranges of x and y are used.

Value

A data frame containing x and y coordinates that describe the inner polygon. The id variable indicates the order of the points.

Examples

x3p <- x3p_subsamples[[1]]
bounds <- x3p_boundary_points(x3p, 2)
polygon <- inside_polygon(bounds$x, bounds$y, 1)

library(ggplot2)
library(dplyr)
#> 
#> Attaching package: ‘dplyr’
#> The following objects are masked from ‘package:stats’:
#> 
#>     filter, lag
#> The following objects are masked from ‘package:base’:
#> 
#>     intersect, setdiff, setequal, union
bounds %>%
  ggplot(aes(x = x, y = y)) +
  geom_point() +
  geom_polygon(data = polygon) +
  theme_bw()