Turf tangents fails in some cases again

[dhivehi]

Sample data for test:

var point = {"type":"Feature","geometry":{"type":"Point","coordinates":[73.5755476513307,0.4323399237340624]},"properties":null};

var poly  = {"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[73.57502193836378,0.43239356638694915],[73.57526333717512,0.43281197906664204],[73.57561738876508,0.43281197906664204],[73.57560129551099,0.4325384015479159],[73.57543499855207,0.4324686661003909],[73.57551010040449,0.43223263842709514],[73.57579441456006,0.43239893065221224],[73.57609482196972,0.4324364805090113],[73.57643278030561,0.4323184666727826],[73.57594998268293,0.4322380026924719],[73.5754779138963,0.4318464113095217],[73.5751184978883,0.4320448891362787],[73.57516141323254,0.4322862810807635],[73.57500048069166,0.43227018828469],[73.57502193836378,0.43239356638694915]]]},"properties":null};

tangents = turf.polygonTangents(point,poly);

[DenisCarriere]

@rowanwins any thoughts?

[rowanwins]

Gday @dhivehi

Thanks for the test case, I'll take a look into it and see what I can find.

[DenisCarriere]

👍 @rowanwins's PR fixes this issue.

[dhivehi]

Again failed in this case also:

var point = {"type":"Feature","geometry":{"type":"Point","coordinates":[73.2258944382542,0.6673910301706059]},"properties":null};
var poly = {"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[73.222696781158,0.672929312864639],[73.223141775131,0.6728221177272928],[73.223743934789,0.6726381749213459],[73.224029146338,0.6725036554756088],[73.224338813812,0.6724074327878782],[73.224860170232,0.6721935244108295],[73.225509744573,0.6720420390183648],[73.226084583476,0.6717472629325556],[73.226458847279,0.6715981449324744],[73.226650858421,0.6715436544821927],[73.227258045226,0.6714184949730679],[73.227445127964,0.6713529476262039],[73.227678178196,0.6712050062728139],[73.228031831012,0.6708426157704537],[73.228146526963,0.6706682403694231],[73.228457655945,0.6700969051734518],[73.228657754266,0.6698443347108025],[73.22884159707,0.6696673096285082],[73.228996763994,0.6695767853640717],[73.229106436541,0.6695525110064722],[73.229149940014,0.6695025217523778],[73.229169917106,0.6693944039229791],[73.229167029882,0.6693046080477387],[73.229084080861,0.6691702157268935],[73.229041067618,0.6691383134431845],[73.228922636334,0.6690945712344814],[73.22885162189,0.6690290941501615],[73.228795706928,0.6690004793602498],[73.228683117007,0.6689698982356589],[73.228615358483,0.6689786536104236],[73.228546747123,0.6690229904581599],[73.228490368271,0.669096495729903],[73.228443036787,0.6694061168332297],[73.228223152757,0.6698214354820493],[73.228165577041,0.6698999456480976],[73.228024344452,0.670025254964898],[73.227903388313,0.6702371606698421],[73.227836480364,0.6703046163993349],[73.227119555512,0.6707099538733416],[73.22668329446,0.6710793258441896],[73.226559966198,0.6711543446100734],[73.226424521696,0.6712119748989664],[73.226177066949,0.6712730394161497],[73.225950830598,0.67127542067891],[73.225655714655,0.6712369330303574],[73.22555065155,0.6711909636509574],[73.225483278402,0.6711332409315816],[73.225406283817,0.6710095253332611],[73.225390645993,0.6709432706487064],[73.225397197529,0.6708261252031065],[73.225457941492,0.6706975144888645],[73.225963781675,0.6703145215167154],[73.226412547476,0.669790217338786],[73.226639346285,0.6696012463551142],[73.226701757055,0.6695209006273473],[73.226727089028,0.6694367056162207],[73.226723397567,0.6693697679729524],[73.226656628151,0.6691877016677381],[73.226566725674,0.669003250939312],[73.226551314195,0.6689166059413054],[73.226568804017,0.668865677272052],[73.226787260285,0.6685663053432478],[73.226824706351,0.668476577946393],[73.226843488025,0.6683734115614755],[73.226823012034,0.668252158733111],[73.226760301619,0.6681455247222345],[73.226612638682,0.6680583776521587],[73.226456208552,0.6680175865484159],[73.226209720597,0.6680410701986119],[73.226154902776,0.668062388064314],[73.226070207392,0.6681289116730795],[73.225768983364,0.6684395167627741],[73.225699240456,0.6684703579247326],[73.22541866541,0.6684446126130723],[73.225309299131,0.6684913460441066],[73.225291081448,0.6684570449487524],[73.225256291015,0.668222172880931],[73.225226394924,0.6681784489895506],[73.225180595009,0.6681526846102344],[73.224978322105,0.6681633512328347],[73.224772984242,0.6682065624897859],[73.224741499018,0.668201968184249],[73.22471701051,0.668173830077734],[73.22470184438,0.66807906378871],[73.224710363746,0.6679383479043537],[73.224809658364,0.6676155759821256],[73.224856696195,0.6673534849849148],[73.224970303437,0.6670680268227471],[73.22512649074,0.6668365082036303],[73.225212097168,0.6667288667304803],[73.225274791718,0.6666840121064155],[73.225625809829,0.6666438269910628],[73.225738127231,0.666611311729028],[73.226002620068,0.6663804677868512],[73.226105900095,0.6662014314291156],[73.226124983675,0.6660370141104295],[73.226040943446,0.6658116107705752],[73.225815226237,0.6655119071691757],[73.225710327836,0.6654167649301144],[73.225627314532,0.6653661538076818],[73.225537743419,0.6653534272697499],[73.225433878899,0.6653717924575773],[73.225318119124,0.665562515457168],[73.225255542633,0.6657391979264418],[73.224956187609,0.6660264320867242],[73.224782510517,0.6663571798607677],[73.224617868401,0.6665229776088211],[73.224439704818,0.6668353595225085],[73.224300938349,0.6672443056588548],[73.22419991164,0.6676913082846596],[73.22406436316,0.6681564543334417],[73.223883887404,0.6690056083385798],[73.22377935234,0.6692590564152425],[73.223676624298,0.6694553729287946],[73.223596730253,0.6695715464665994],[73.223541862338,0.6696966344853763],[73.223345681691,0.6704022315888665],[73.223258191582,0.670645296332097],[73.222985252214,0.6715456004246505],[73.22285381536,0.6718248328859886],[73.222686846515,0.6721174107883314],[73.222454455099,0.6724137943929662],[73.222098727673,0.6728239052963403],[73.222041913757,0.6729435103004278],[73.222061824868,0.6729818899183755],[73.222099328875,0.6729992722487737],[73.222397657256,0.6729767617070905],[73.222696781158,0.672929312864639]]]}};
tangents = turf.polygonTangents(point,poly);

[rowanwins]

Ok @dhivehi

So I've done a bit of digging. It looks like the fix I previously applied broke the module for other cases, and the previous implementation was more accurate.

It looks like there is a more fundamental problem with the algorithm when your input point is inside the concave hull of the polygon and lower than the first segment. My head is still grappling with the maths but I'll see what we can work out, in the meantime I suggest we revert back to the original code

[DenisCarriere]

Interesting... I'm good with reverting it back 👍 The more test cases we have the more robust the library will become.

[rowanwins]

This page (where the orig implementation came from) also lists a sweepline approach, apparently this is faster but Im not sure if it'll produce different results.

[rowanwins]

Think I've now got this resolved by #1174 , has been released as v5.1.5 to npm