R: Calculate the centroid of a polygon.

getCentroid {venn} | R Documentation

## Calculate the centroid of a polygon.

### Description

This function takes a list of dataframes or a matrices containing x and y values, which define zones (polygons), and calculates their centroids.

### Usage

    getCentroid(data)

### Arguments

`data` | A matrix or a dataframe with two columns, for x and y coordinates

### Details

Most of the coordinates for the intersection labels in this package were calculated using the formula for a centroid of a non-self-intersecting closed polygon, approximated by 10 vertices.

### Value

A list with x and y coordinates, for each zone in the input list.

### References

Centroid. (n.d.). In Wikipedia. Retrieved January 06, 2016, from https://en.wikipedia.org/wiki/Centroid

### Examples

    venn("0110")

    # centroid for the intersection "0110" in a 4 set diagram
    centroid <- getCentroid(getZones("0110"))[[1]]

    text(centroid[1], centroid[2], labels = "0110", cex = 0.85)

    # centroids for the two zones in the "E not A" zones
    venn(5)
    area <- getZones("0---1") # list of length 2

    polygon(area[[1]], col="lightblue")

    polygon(area[[2]], col="lightblue")

    text(do.call("rbind", getCentroid(area)),
         labels = c("zone 1", "zone 2"), cex = 0.85)

[Package venn version 1.7 Index]