getAreaOfPolygon returns a number when I pass an unclosed area

[kasir-barati]

Hi dear reader, When I execute this code IDK why but for some reason for the second one also returns a number though it is not even a closed area. So my question is that if this is an expected behaviour and OK. BTW based on my understanding it should not work like that, I mean it is not even a closed are to begin with:

const geolib = require("geolib");

// 1
console.log(
  geolib.getAreaOfPolygon([
    [7.453635617650258, 51.49320556213869],
    [7.454583481047989, 51.49328893754685],
    [7.454778172179346, 51.49240881084831],
    [7.453832678225655, 51.49231619246726],
    [7.453635617650258, 51.49320556213869],
  ])
);

// 2
console.log(
  geolib.getAreaOfPolygon([
    {
      latitude: -72.2781577,
      longitude: 42.9288483,
    },
    {
      latitude: -72.2864358,
      longitude: 42.928252,
    },
    {
      latitude: -72.2877233,
      longitude: 42.9247012,
    },
    {
      latitude: -72.2817152,
      longitude: 42.9237898,
    },
  ])
);

Here is what I meant by not closed area, as you can see in the uploaded image the starting point - the first point on the right top corner - is not even close to the ending point -- the last point in the bottom right corner:

Here is my work env conf:

geolib: 3.3.4
node: 20.3.1
npm: 9.6.7
OS: Darwin Kernel Version 22.5.0 arm64

[kasir-barati]

Can you please let me know if this is a bug or not dear @manuelbieh? IMO it is but still it is a good idea to be sure 😅

[kasir-barati]

OK, I am coming from the future. In this part of code we are closing it

geolib/src/getAreaOfPolygon.ts

Lines 16 to 36 in 26ec179

	for (let i = 0; i < points.length; i++) {
	if (i === points.length - 2) {
	lowerIndex = points.length - 2;
	middleIndex = points.length - 1;
	upperIndex = 0;
	} else if (i === points.length - 1) {
	lowerIndex = points.length - 1;
	middleIndex = 0;
	upperIndex = 1;
	} else {
	lowerIndex = i;
	middleIndex = i + 1;
	upperIndex = i + 2;
	}
	const p1lon = getLongitude(points[lowerIndex]);
	const p2lat = getLatitude(points[middleIndex]);
	const p3lon = getLongitude(points[upperIndex]);
	area += (toRad(p3lon) - toRad(p1lon)) * Math.sin(toRad(p2lat));
	}

Though IMO this is not OK, and also the documentation lacks clarity about these kind of underlying implementations.

I hope someone will just address this GitHub issue