Polygon Utilities

This JavaScript module provides a set of utility functions for calculating properties of polygons using geographical coordinates. These properties include the area and centroid of a polygon, checking if a point is inside a polygon and determining an internal label point for polygons.

ES6 Import

import {
  polygonArea,
  polygonCentroid,
  isPointInPolygon,
  polygonInternalLabel,
} from "polygon-property-utils";

Functions

polygonArea(coordinates: Position[]): number

Calculates the area of a polygon provided as an array of Position coordinates. The function requires that the polygon is closed, i.e., the last coordinate is the same as the first.

Parameters:

• coordinates: Array of [longitude, latitude] pairs.

Returns:

• The area of the polygon in square meters (m^2).

polygonCentroid(coordinates: Position[]): Position | null

Calculates the centroid (geometric center) of a polygon defined by an array of Position coordinates.

Parameters:

• coordinates: Array of [longitude, latitude] pairs.

Returns:

• A Position array [longitude, latitude] representing the centroid, or null if the polygon is not closed.

isPointInPolygon(point: Position, coordinates: Position[]): boolean

Determines whether a given point is inside a polygon.

Parameters:

• point: A Position [longitude, latitude].
• coordinates: Array of [longitude, latitude] pairs defining the polygon.

Returns:

• true if the point is inside the polygon, false otherwise.

polygonInternalLabel(coordinates: Position[]): Position | null

Calculates an ideal point for labeling purposes inside a polygon. (Locates closest boundary from the centroid and draws a line through the polygon to find the next intersection and returns a location 1/3 distance from the first intersection towards the second intersection.)

Parameters:

• coordinates: Array of [longitude, latitude] pairs defining the polygon.

Returns:

• A Position [longitude, latitude] that is suitable for placing a label inside the polygon, or null if no suitable point can be found.

Types

Position

A tuple representing a geographical coordinate, where the first element is the longitude and the second is the latitude.

type Position = [number, number];