Hey @samuelarbibe i've found an issue with this fix. I'll test out a fix and get back to you.

Hey @samuelarbibe i've found an issue with this fix. I'll test out a fix and get back to you.

I'm curious. Let me know :)

@samuelarbibe I think you focused too much on advanced use cases and forgot the simple ones 😂
This implementation fails for this use case:

Sandbox link: https://turf-sandbox.netlify.app/?gist=6ce3e4e6d674e6dd9c92c5265b6a25e0

The issue is this line not returning any segments when there are no intersections.

const lineSegments = turf.lineSplit(turf.feature(linestring), turf.feature(polygon));

Here is a potential fix:

// ...
  const lineSegmentsOrLineString = lineSegments.features.length > 0 ? lineSegments.features : [turf.feature(linestring)];

  for (const lineSegment of lineSegmentsOrLineString) {
    const midpoint = turf.midpoint(
      lineSegment.geometry.coordinates[0],
      lineSegment.geometry.coordinates[1]
    );
// ...

Fix sandbox: https://turf-sandbox.netlify.app/?gist=57378d936e774ac353de86e975060bf9

Thank you.... got too focused on the complicated cases 😅.
Implemented a fix similar to you suggestion, with a little fix (The problem is that if the line sting has 2 or more vertices on the boundary of the polygon, the midpoint might be contained by the polygon, so I split the linestring into multiple linestring, one per segment).

Would you mind doing some rewording of the documentation while you're here? The "exact opposite result" phrasing isn't very satisfying (and I'm not sure it's true anyway if taken literally).

From

Boolean-contains returns True if the second geometry is completely contained by the first geometry. The interiors of both geometries must intersect and, the interior and boundary of the secondary (geometry b) must not intersect the exterior of the primary (geometry a). Boolean-contains returns the exact opposite result of the @turf/boolean-within.

returns true/false

To

Tests whether geometry a contains geometry b. The interiors of both geometries must intersect, and the interior and boundary of geometry b must not intersect the exterior of geometry a.

booleanContains(a, b) is equivalent to booleanWithin(b, a)

returns true if geometry a contains geometry b, false otherwise

Happy to hear it if you have other suggestions as well!

Thanks for your work on this too @Janickvw ⭐

fix similar to you suggestion, with a little fix (The problem is that if the line sting has 2 or more vertices on the boundary of the polygon, the midpoint might be contained by the polygon, so I split the linestring into multiple linestring, one per segment).

Sorry to be a pain, since I know this is already merged. But i've read this comment a few times and still don't understand it. Seems redundant to split a line segment that completely overlaps a boundary? Do you have a graphic or picture you could use to demonstrate?

Sorry to be a pain, since I know this is already merged. But i've read this comment a few times and still don't understand it. Seems redundant to split a line segment that completely overlaps a boundary? Do you have a graphic or picture you could use to demonstrate?

Hey! no problem.

the problem is that the split function isn't sufficient.
For example, this scenario:

The split function will return in this case a single line string feature:

And using a midpoint on the whole line string may result in faulty cases.

The new function created, splitLineIntoSegmentsOnPolygon, splits the line string on the polygon - but makes sure to return individual segments.

  const lineSegmentsOrLineString = lineSegments.features.length > 0 ? lineSegments.features : [turf.feature(linestring)];

is insufficient, as it assumes the split function splits in a certain way.
For reference - the LineIsContainedByPolygonWithSegmentOnBoundary test fails when using this logic.

Sorry to be a pain, since I know this is already merged. But i've read this comment a few times and still don't understand it. Seems redundant to split a line segment that completely overlaps a boundary? Do you have a graphic or picture you could use to demonstrate?

Hey! no problem.

the problem is that the split function isn't sufficient. For example, this scenario:

The `split` function will return in this case a single line string feature: And using a midpoint on the whole line string may result in faulty cases.

The new function created, splitLineIntoSegmentsOnPolygon, splits the line string on the polygon - but makes sure to return individual segments.

  const lineSegmentsOrLineString = lineSegments.features.length > 0 ? lineSegments.features : [turf.feature(linestring)];

is insufficient, as it assumes the split function splits in a certain way. For reference - the LineIsContainedByPolygonWithSegmentOnBoundary test fails when using this logic.

Ah ok interesting. Thanks for the reply @samuelarbibe!

Thanks for doing that followup @Janickvw and @samuelarbibe