Not sure is it the same problem, but if we have point from "nearestPointOnLine" and check it with "booleanPointOnLine", we wil get the "false" mostly. Mayby I am missing something in the documentation, but think what both functions are should be connected. I mean, if we get "nearestPointOnLine", we can prove it by using "booleanPointOnLine".
I am changed @kristiansvenssonwsp fiddle a little bit to show this behaiver.

@zazagag I'm running into this same problem, kind of problematic as I need to generate a point on a multiline then figure out which segment of the multiline it's on.

Also seeing this issue. nearestPointOnLine and booleanPointOnLine should surely be connected as described above.

This could well be the difference between spherical and ellipsoidal calculations. Using the two different methods in geopy produces the results mentioned above: using great_circle gives (4353m) vs geodesic (4367).

Have opened discussion #2470 on the best way to go forward. One option would be to port geopy's distance formula to Turf. However am seeking advice on which technique should become the default if we offer multiple options.

Hi @JamesLMilner @rowanwins @twelch . Will take a look at this if you'd like to assign my way.

The length accuracy part of this should be addressed by #2476. User needs to pass in the appropriate ellipsoid for underlying distance() calculation to use.

@sweco-sekrsv. At the moment fixing the length issue will have to stay on the back burner. Turf is already using a mix of planar and spherical calculations, and adding spheroidal also ... 🤯 Our focus is on making Turf internally consistent first, then look at parity with other tools once that's stable.

@zazagag, @ngottlieb, @AppKidd nearestPointOnLine was making inaccurate calculations, as was booleanPointOnLine. So they were both wrong, and in different ways, which is why they weren't matching up. A fix for nearestPointOnLine should arrive soon, and then after that will move on to booleanPointOnLine.

Given this issue covers a couple of different modules and outcomes, will close based on the length module being "not planned". nearestPointOnLine is covered by #1878, and booleanPointOnLine by #1362.