Incorrect/weird results from h3SetToMultiPolygon

[Tama Pugsley]

I'm getting some weird results from h3SetToMultiPolygon when passing large numbers of h3 indexes (in these examples the h3 cells are all adjacent). There are two issues:

1. When the polygon array is returned there are a number of single point arrays. e.g.

h3Ids:
["8132fffffffffff","812e7ffffffffff","81303ffffffffff","815a3ffffffffff","814f7ffffffffff","81733ffffffffff","81687ffffffffff","814afffffffffff","8133bffffffffff","812f3ffffffffff","814e7ffffffffff","8130fffffffffff","815afffffffffff","8132bffffffffff","814bbffffffffff","812e3ffffffffff","81777ffffffffff","814f3ffffffffff","814abffffffffff","81337ffffffffff","812efffffffffff","814e3ffffffffff","815abffffffffff","81327ffffffffff","814b7ffffffffff","812fbffffffffff","81773ffffffffff","814efffffffffff","81317ffffffffff","815b7ffffffffff","814a7ffffffffff","81333ffffffffff","815a7ffffffffff","81737ffffffffff","81323ffffffffff","814fbffffffffff","814b3ffffffffff","812f7ffffffffff","814ebffffffffff","81313ffffffffff","815b3ffffffffff","814a3ffffffffff","8123bffffffffff","81237ffffffffff","81233ffffffffff","8147bffffffffff","8146fffffffffff","8146bffffffffff","81223ffffffffff","81463ffffffffff","81473ffffffffff","81477ffffffffff","81467ffffffffff","815dbffffffffff","815d3ffffffffff","815cbffffffffff","815c3ffffffffff","8137bffffffffff","815bbffffffffff","81373ffffffffff","8136bffffffffff","81363ffffffffff","8171bffffffffff","81717ffffffffff","81713ffffffffff"]

Gives this result:
[ [ [ [ 43.816094965537175, 142.3058437365082 ], [ 47.94353494620575, 140.81932027711576 ], [ 48.30438780776227, 137.965723000237 ], [ 48.41801789173907, 134.76393627595755 ], [ 45.253613490980094, 131.7744009814935 ], [ 45.09643436908035, 125.98114176677377 ], [ 47.997962809385406, 122.1525950681968 ], [ 47.30945130281312, 116.21289563713783 ], [ 43.25414167974314, 115.50113901102061 ], [ 41.14827082786993, 119.13690952882241 ], [ 38.614966776615006, 118.5828850895855 ], [ 37.42985448428109, 118.86929883406582 ], [ 36.20528264541884, 121.690153924224 ], [ 36.005614448071924, 123.16276457697893 ], [ 32.66144519495384, 124.02055612683286 ], [ 29.89298533869355, 120.503393859958 ], [ 26.20027606045547, 121.34751445935747 ], [ 24.728661050965936, 119.64146543031175 ], [ 23.50895195973631, 117.99047716641068 ], [ 19.252194904738655, 118.80300158646772 ], [ 18.127070267319834, 123.02355515221002 ], [ 13.797500809062361, 123.85482415801255 ], [ 10.736966167684393, 120.449366342475 ], [ 6.2891846753414375, 121.26764633911117 ], [ 4.76343118357537, 125.5023153387887 ], [ 7.805398745803346, 129.0449200915637 ], [ 6.19767652780886, 133.49441060685513 ], [ 9.23145267029969, 137.1970727246292 ], [ 7.537486471095007, 141.69432910913807 ], [ 10.472716898667054, 145.410940917621 ], [ 8.701739974658008, 149.7748737561887 ], [ 4.084015752678338, 150.44123001544202 ], [ 2.3920322085174597, 154.598935323174 ], [ 5.189055516512115, 158.0067643262748 ], [ 3.50810422466813, 161.8156148096885 ], [ 6.119591258608643, 164.93539603741024 ], [ 4.4670316097845255, 168.3352524578736 ], [ 4.467031609784517, 168.3352524578736 ], [ 6.172978893164634, 172.0341823693935 ], [ 4.248592317017831, 175.46041201203371 ], [ 5.8899217543139155, 179.21716082489448 ], [ 5.889921754313889, 179.21716082489448 ], [ 2.9040374505798128, -178.0251966524985 ], [ 3.821024494330419, -174.31673738369324 ], [ 7.972793830841406, -173.38014762578527 ], [ 9.060308038526605, -169.29312998396932 ], [ 5.767146686378422, -166.16940101623453 ], [ 6.766536253596447, -161.77338167921764 ], [ 3.3357348575173495, -158.59967491814012 ], [ 4.260374459536216, -154.0294052002189 ], [ 8.71898308656318, -152.5335322367957 ], [ 9.628747217956542, -147.80006555587835 ], [ 14.110797540904425, -146.16007687374923 ], [ 17.737530353545214, -149.3676428224656 ], [ 22.166939007405805, -147.69594788211106 ], [ 25.669243623986258, -151.04796662686522 ], [ 29.891830084602514, -149.34707529879068 ], [ 30.56995088296885, -144.17342232410294 ], [ 34.454167617014946, -142.3232078622538 ], [ 37.68759229063255, -145.7463690434673 ], [ 41.20828589932378, -143.84631120128412 ], [ 44.09362423911827, -147.45009391663316 ], [ 43.44325276436555, -153.03739182353246 ], [ 43.44325276436556, -153.03739182353243 ], [ 46.9088746957617, -156.03631344405528 ], [ 46.51349897531834, -161.56979335131368 ], [ 49.895974148750696, -165.61336675442524 ], [ 49.05085282910133, -171.87311046039585 ], [ 44.74985555511408, -173.25136162888563 ], [ 43.33462463706693, -179.170112546831 ], [ 46.18001465709014, 175.62099681678237 ], [ 44.17622039141846, 169.66101739290986 ], [ 46.48282657751592, 163.91021485526238 ], [ 43.912304017571394, 158.38289640953528 ], [ 45.62266462732751, 152.54480605394903 ], [ 42.63340688235615, 147.81728377284588 ] ] ], [ [ [ 27.949605976503907, 142.4332217566576 ] ] ], [ [ [ 34.33115860097916, 132.30837745804206 ] ] ], [ [ [ 12.194726726167971, 160.7733897026288 ] ] ] ]

The first polygon is accurate but the others are single points and seem unnecessary. Not a big deal as I can easily filter these out. This doesn't seem to happen at lower H3 resolutions.

---

2. Occasionally I am only getting single point returns (i.e. no actual polygon).

For example with these h3 ids:
[ "816efffffffffff", "8126bffffffffff", "8148fffffffffff", "8113bffffffffff", "8122fffffffffff", "810c3ffffffffff", "8150bffffffffff", "815c3ffffffffff", "8126fffffffffff", "81493ffffffffff", "81363ffffffffff", "81457ffffffffff", "81233ffffffffff", "810c7ffffffffff", "8150fffffffffff", "815c7ffffffffff", "81273ffffffffff", "81497ffffffffff", "81367ffffffffff", "81237ffffffffff", "810cbffffffffff", "81513ffffffffff", "815cbffffffffff", "8149bffffffffff", "8136bffffffffff", "8123bffffffffff", "810cfffffffffff", "81517ffffffffff", "811c3ffffffffff", "815cfffffffffff", "816c3ffffffffff", "8127bffffffffff", "8136fffffffffff", "81463ffffffffff", "8151bffffffffff", "81703ffffffffff", "815d3ffffffffff", "81373ffffffffff", "81467ffffffffff", "811cbffffffffff", "81707ffffffffff", "815d7ffffffffff", "816cbffffffffff", "81283ffffffffff", "81377ffffffffff", "8146bffffffffff", "811cfffffffffff", "815dbffffffffff", "81287ffffffffff", "8137bffffffffff", "8146fffffffffff", "811d3ffffffffff", "816d3ffffffffff", "8128bffffffffff", "81473ffffffffff", "811d7ffffffffff", "81713ffffffffff", "8128fffffffffff", "81477ffffffffff", "81123ffffffffff", "811dbffffffffff", "81717ffffffffff", "816dbffffffffff", "81293ffffffffff", "8147bffffffffff", "81127ffffffffff", "81793ffffffffff", "810ebffffffffff", "8171bffffffffff", "81297ffffffffff", "81797ffffffffff", "8112bffffffffff", "816e3ffffffffff", "8129bffffffffff", "81483ffffffffff", "8179bffffffffff", "8112fffffffffff", "81447ffffffffff", "81223ffffffffff", "816e7ffffffffff", "81263ffffffffff", "81487ffffffffff", "81227ffffffffff", "81503ffffffffff", "816ebffffffffff", "81267ffffffffff", "8148bffffffffff", "81137ffffffffff", "8122bffffffffff", "81507ffffffffff", "815fbffffffffff", "814cbffffffffff", "812a7ffffffffff", "8139bffffffffff", "81453ffffffffff", "81677ffffffffff", "81547ffffffffff", "811b7ffffffffff", "812abffffffffff", "814cfffffffffff", "8167bffffffffff", "8154bffffffffff", "811bbffffffffff", "812afffffffffff", "814d3ffffffffff", "813a3ffffffffff", "8145bffffffffff", "8154fffffffffff", "812b3ffffffffff", "814d7ffffffffff", "81183ffffffffff", "813a7ffffffffff", "81277ffffffffff", "81553ffffffffff", "814dbffffffffff", "812b7ffffffffff", "81187ffffffffff", "813abffffffffff", "81557ffffffffff", "812bbffffffffff", "8118bffffffffff", "813afffffffffff", "816c7ffffffffff", "8155bffffffffff", "81743ffffffffff", "8118fffffffffff", "813b3ffffffffff", "8159bffffffffff", "81193ffffffffff", "813b7ffffffffff", "81563ffffffffff", "81197ffffffffff", "813bbffffffffff", "81067ffffffffff", "817c7ffffffffff", "81567ffffffffff", "81343ffffffffff", "810e3ffffffffff", "8119bffffffffff", "815e3ffffffffff", "816d7ffffffffff", "81383ffffffffff", "817cbffffffffff", "8156bffffffffff", "81347ffffffffff", "81753ffffffffff", "810e7ffffffffff", "815e7ffffffffff", "817cfffffffffff", "8156fffffffffff", "8134bffffffffff", "81663ffffffffff", "81757ffffffffff", "8180fffffffffff", "811a3ffffffffff", "815ebffffffffff", "8138bffffffffff", "8134fffffffffff", "81573ffffffffff", "81667ffffffffff", "81443ffffffffff", "8175bffffffffff", "810efffffffffff", "811a7ffffffffff", "815efffffffffff", "81077ffffffffff", "81353ffffffffff", "81577ffffffffff", "8166bffffffffff", "815f3ffffffffff", "811abffffffffff", "814c3ffffffffff", "81393ffffffffff", "81357ffffffffff", "8157bffffffffff", "8144bffffffffff", "810f7ffffffffff", "815f7ffffffffff", "811afffffffffff", "812a3ffffffffff", "8135bffffffffff", "8144fffffffffff", "81673ffffffffff", "81543ffffffffff", "811b3ffffffffff" ]

I get:
[ [ [ [ 43.44325276436555, -153.03739182353246 ] ] ], [ [ [ 14.48240061773311, -65.76882190787967 ] ] ], [ [ [ 19.358823435394214, -75.99854824376126 ] ] ], [ [ [ 8.931891500446854, -127.11406580207421 ] ] ], [ [ [ 59.16948256665965, -139.68359348160976 ] ] ], [ [ [ 40.975558199255886, -54.879012779249344 ] ] ], [ [ [ 31.285608665560563, -134.10648897177788 ] ] ], [ [ [ 29.30037465923499, 0.2609468260311339 ] ] ], [ [ [ 41.45713981733575, -138.450291223663 ] ] ], [ [ [ 29.82877615972559, -1.240802016513824 ] ] ], [ [ [ 31.877885956365837, -62.02252554784451 ] ] ], [ [ [ 11.545295975414758, -4.01399844347046 ] ] ] ]

i.e. no actual polygon, just a series of points — seems like a bug?

[Nick Rabinowitz]

Sorry for the long silence here. Investigating now - I believe this is due to a bug in the core H3 lib that has a non-trivial fix that we're currently working on, but I need to verify.

[Tama Pugsley]

No worries, I figured as much! I was trying to use it to calculate the bounds of a set of adjacent h3 cells (bit overkill), I've implemented a workaround that works for our purposes.

Thanks for the reply!