polygonToCells returns Error1 (specific error is not available) but polygonToCellsExperimental works fine

[dgnemo]

In the application I am working on I am observing frequent cases of polygonToCells invocations returning

Error 1: The operation failed but a more specific error is not available

I suspect this happens with Polygons that are near or include one of the poles, but I am not sure as I have not inspected all the errors I am receiving.

These polygons are all approximations of elliptical shapes. If I approximate the shape with > 4 points, polygonToCells fails.

When I approximate with 4 points it usually works.

An example of these shapes is:

h3.LatLngPoly([
    (-54.057708, 64.153144),
    (-73.063939, 150.650215),
    (-60.97747, -98.008123),
    (-42.548997, -40.753213),
    (-39.497647, 10.681521)
])

Interesting to note that polygon_to_cells_experimental seems to work fine.

(unfortunately I cannot test it extensively as the original application is in Java and latest h3-java release in Maven does not include the new experimental methods).

Questions:

1. are there known limitations in polygonToCells ?
2. is it known/expected that polygon_to_cells_experimental can solve polygons that the original methods cannot?

PS: looking forward for h3-java to release new versions including experimental methods!

[KirkDybvik]

A few limitations found when looking at similar issue #945 (comment)

Looking at C source code for 4.2, the polygonToCells calls bboxesFromGeoPolygon, and that calls bboxFromGeoLoop. Looking deeper, see the comment in polygonAlgos.h for GENERIC_LOOP_ALGO stating "Does not currently support polygons containing a pole."

If this truly is the cause, it may be a good idea to document these limitations on https://h3geo.org/docs/api/regions#polygontocells

/**

Create a bounding box from a simple polygon loop.
Known limitations:
Does not support polygons with two adjacent points > 180 degrees of
longitude apart. These will be interpreted as crossing the antimeridian.
Does not currently support polygons containing a pole.
@param loop Loop of coordinates
@param bbox Output bbox
*/
void GENERIC_LOOP_ALGO(bboxFrom)(const TYPE *loop, BBox *bbox) {