lineIntersectsLine is not commutative

Hi,

I noticed this:

const line1 = [
  [50.054358, 8.693184],
  [50.055604, 8.685873]
];
const line2 = [
  [50.054228, 8.69338],
  [50.054358, 8.693184]
];
lineIntersectsLine(line1, line2);
// false
lineIntersectsLine(line2, line1);
// true

Note that the start of line1 and the end of line2 are identical.

What do you think is the expected result? Since the lines share a point, they arguably do intersect. However my use case is around multiple lines fanning out from a single point and I don’t want to count those as intersecting.

I’d suggest adding a parameter excludeEndpoints that determines wether sharing a start/end-point should count as intersecting. What do you think?

I can probably open a PR if we decide on something.

Kind regards, yeldiRium

[HarryStevens]

Thanks @yannbriancon. I’ve merged your PR.

[yannbriancon]

@HarryStevens Thanks for this great library!

I am though having issues with the fact that if the end point of one line is on the other line but is not its beginning or end, the lines are not detected as intersecting.

Here is an example: line1 = [a, b] = [[0, 0], [1, 0]] line2 = [c, d] = [[0.5, -1], [0.5, 0]]

a---d---b
    |
    |
    c

lineIntersectsLine([[0, 0], [1, 0]], [[0.5, -1], [0.5, 0]]) // returns false

Here is a PR fixing the issue https://github.com/HarryStevens/geometric/pull/23 but reach out if you have another fix in mind