Tesselation sometime fails for small regions at high latitude
The fix for critical issue #792 (closed) was not sufficient. In very rare case, and unfortunately cases difficult to reproduce (I am currently not able to them at all), ellipsoid tesselation fails at high latitude. Tesselation works by seeding a mesh with a single node arbitrarily extracted from the region, then expanding the mesh by looking at neighboring points until the two following conditions are met: 1) all neighbors are outside of the zone 2) there are no peaks in the region that escapes between two mesh nodes (like a long and thin peninsula for a region representing an island)
When a region is path-connected, this first step of the tesselation algorithm is sufficient to ensure the full region is covered and some grid points can be selected to construct a set list of regular tiles.
When a region is not path-connected (like when the region corresponds to an archipelago with one region split into several sub-regions), this first step is insufficient as it may cover only one of the islands and miss the other ones which are farther away. For this reason, the algorithm includes a second step to handle this case: the generated tile is removed from the initial region, and if the difference (with set theory semantics) is not empty, then a new iteration of the loop containing steps 1 and step 2 is performed, the seeding point for the new iteration being extracted from the difference, ensuring the new mesh will cover new areas. The meshes resulting from all iterations of this loop are merged together, taking care of cases where they intersect each other (in the archipelago example, this happens when islands are far enough to trigger several iterations, but close enough that some mesh happens to intersect other ones).
The critical bug happens when computing the regions difference. In rare cases (not fully characterized yet, but which seem to happen at high latitudes in along-track tiling), small path-connected regions lead to non-empty differences despite they are really fully covered by a single tile.