coords array: polygon with holes vs multipolygon

[codeofsumit]

Hey there, I'm trying to replace turfs difference and intersect with your library in leaflet.pm (drawing plugin for leaflet) due to size.
To illustrate the problem I've included gifs of using your library.

When using difference, I'm having a bit trouble figuring out if the result is a MultiPolygon or a Polygon with a hole.
In your examples, you always expect it to be a Multipolygon but if you treat a hole that way - two layers are being drawn.

Using diff on a polygon when the result is a regular polygon

Using diff on a polygon, cutting it in half, and the result is a multipolygon:

Using diff on a polygon, cutting a hole in it. The resulting coords array looks exactly like a multipolygon, so both are getting drawn:

How would you recommend to find out if it's a hole or a multipolygon?

[DenisCarriere]

@codeofsumit Side topic, we would be using the martinez library for TurfJS's intersect & difference if the hole in the MultiPolygon issue get sorted out.

👍

@rowanwins Could we use martinez right now?

[rowanwins]

Mmm at the moment I think we're just trying to sort out a performance bug @DenisCarriere . We could try and incorporate it into turf and see how the tests and benchmark faired, I'll try and take a look at that this week and will report back

[rowanwins]

Actually just dropping another note in here, I've attempted to replace jsts within turf/difference but I didn't have much joy. There still seems to be some issues with multipolygons as well as polygons with holes. The test suite for turf was very handy for identifying the issues so that was positive :)

[w8r]

difference is broken, as I stated before, but it wasn't before we made changes, so I think we can fix it.

[rowanwins]

ahh sorry @w8r I misunderstood that other comment you left, I'll try getting one of the other operations into turf and see if I uncover anything else

[rowanwins]

No joy with union either @w8r when using this input I get this output, the hole is nested too deeply

[w8r]

Very cool that you have examples!

[codeofsumit]

hey guys, just wanted to ask how it's going on this? @w8r you mentioned difference is broken - can you let me/us know if this will change short-term or stay this way for the foreseeable future (considering your own time working on it if no surprise PR comes in)?

[rowanwins]

slow is the answer @codeofsumit :(

I'm currently tied up with some turf work for the next week but once that is sorted this is going to be my main priority.

[w8r]

I am sorry it goes so slow, but I really work on it sporadically. Maybe we can really plan a session when we can sit and resolve that stuff once and for all. I really believe we have lots of test cases and now that the code is simpler, we can fix the problem. Actually holes marking was done by indexing and in the paper it even supports 'islands' as 'holes' of 'holes', which might be the flaw. I really need to sit down and look at it closely

[codeofsumit]

any updates here?

[rowanwins]

Hi @codeofsumit

I've made some progress which is available in #42 , although there are still a couple of outstanding issues that occur in very isolated situations. I would say that in 95% of situations you'll likely get a good and predictable result, so whether that is enough for you I'm not sure...

[rowanwins]

Oh and ps in the branch mentioned above everything is output as a multipolygon. It may be there that the output only have 1 polygon, but this was we can provide a consistent output in terms of nesting etc.

[codeofsumit]

@DenisCarriere is it enough to get it into turf?

[rowanwins]

It's really close, but not quite sufficient for my liking.
FYI I'm involved in Turf as well, as soon as all this work is tidied up I'll make sure it's incorporated in Turf asap.

[DenisCarriere]

👍 Agreed! We will definitely add Martinez in Turf! This will open up many new doors for new spatial operations.

Looking forward to that day! 🎉

[w8r]

will be fixed in #42