Incorrect fix_geojson result for a geometry in Saudi Arabia #182
Description
I've been trying out this library to help clean up a data source (Who's on First) which I know has a bunch of abnormal GeoJSON. I'm actually not 100% sure what specific cases fix_geojson is supposed to addressed, so I just ran it on the entire dataset to see what'd happen and I found some cases where it will invert a geometry so it covers the entire world, sans the original area it was supposed to cover 😅
This neighbourhood in Saudi Arabia stood out as a minimal reproducible example as it's a fairly simple polygon.
{
"id": 1361026217,
"type": "Feature",
"properties": {
"edtf:cessation":"uuuu",
"edtf:inception":"uuuu",
"geom:area":0.000548,
"geom:area_square_m":0.0,
"geom:bbox":"41.661835,27.536652,41.701686,27.556499",
"geom:latitude":27.547189,
"geom:longitude":41.683172,
"gn:admin1_code":"13",
"gn:asciiname":"Sadyan",
"gn:country_code":"SA",
"gn:dem":990,
"gn:feature_class":"P",
"gn:feature_code":"PPL",
"gn:geonameid":395249,
"gn:latitude":27.5463,
"gn:longitude":41.69747,
"gn:modification_date":"2018-03-08",
"gn:name":"\u015eady\u0101n",
"gn:population":0,
"gn:timezone":"Asia/Riyadh",
"iso:country":"SA",
"lbl:latitude":27.547922,
"lbl:longitude":41.683172,
"lbl:max_zoom":18.0,
"mz:hierarchy_label":1,
"mz:is_current":1,
"mz:min_zoom":15.0,
"name:ara_x_preferred":[
"\u0633\u062f\u064a\u0627\u0646"
],
"name:ara_x_variant":[
"\u0635\u062f\u064a\u0627\u0646"
],
"name:eng_x_preferred":[
"Sadyan"
],
"name:und_x_variant":[
"\u015eady\u0101n"
],
"reversegeo:latitude":27.547922,
"reversegeo:longitude":41.683172,
"src:geom":"whosonfirst",
"src:geom_alt":[
"geonames"
],
"src:lbl_centroid":"whosonfirst",
"wof:belongsto":[
102191569,
85632253,
421190323,
1108720703,
85676831
],
"wof:breaches":[],
"wof:concordances":{
"gn:id":395249
},
"wof:country":"SA",
"wof:geomhash":"8f0c280a5d19b116d263f4942ff95891",
"wof:hierarchy":[
{
"continent_id":102191569,
"country_id":85632253,
"county_id":1108720703,
"locality_id":421190323,
"neighbourhood_id":1361026217,
"region_id":85676831
}
],
"wof:id":1361026217,
"wof:lastmodified":1660235491,
"wof:name":"Sadyan",
"wof:parent_id":421190323,
"wof:placetype":"neighbourhood",
"wof:repo":"whosonfirst-data-admin-sa",
"wof:superseded_by":[],
"wof:supersedes":[
1209293959
],
"wof:tags":[]
},
"bbox": [
41.661835,
27.536652,
41.701686,
27.556499
],
"geometry": {"coordinates":[[[41.701686,27.555683],[41.677091,27.556499],[41.701686,27.555683],[41.701676,27.552681],[41.694555,27.537487],[41.69456,27.536652],[41.684332,27.538833],[41.683195,27.539543],[41.674979,27.541187],[41.672853,27.540324],[41.671549,27.538989],[41.671067,27.537625],[41.665152,27.538274],[41.664217,27.538102],[41.661835,27.538401],[41.66299,27.541284],[41.667426,27.54781],[41.67182,27.554058],[41.674274,27.555888],[41.677091,27.556499],[41.701686,27.555683]]],"type":"Polygon"}
}If you paste this into geojson.io, everything displays fine, but of you look closely (scroll down to the coordinates) there's a little warning that it doesn't follow the right hand rule. Basically, winding order is wrong.
If you feed this into antimeridian.fix_geojson, it does print a FixWindingWarning to the console to this effect. However, if you look at the coordinates, it's clear something is a bit off. Basically it inverts the intended shape.
{
"id": 1361026217,
"type": "Feature",
"properties": {},
"bbox": [41.661835, 27.536652, 41.701686, 27.556499],
"geometry": {
"type": "Polygon",
"coordinates": [
[
[-180.0, 90.0],
[-180.0, -90.0],
[ 180.0, -90.0],
[ 180.0, 90.0],
[-180.0, 90.0]
],
[
[41.701685999999995, 27.555683],
[41.67709099999999, 27.556499],
[41.674274, 27.555888],
[41.67182, 27.554058],
[41.667426000000006, 27.54781 ],
[41.66299000000001, 27.541284],
[41.661834999999996, 27.538401],
[41.66421700000001, 27.538102],
[41.665152000000006, 27.538274],
[41.671066999999994, 27.537625],
[41.671549, 27.538989],
[41.672853, 27.540324],
[41.67497900000001, 27.541187],
[41.68319500000001, 27.539543],
[41.68433199999998, 27.538833],
[41.694559999999996, 27.536652],
[41.69455500000001, 27.537487],
[41.70167599999999, 27.552681],
[41.701685999999995, 27.555683],
[41.67709099999999, 27.556499],
[41.701685999999995, 27.555683]
]
]
}
}I can definitely understand the behavior here since it's not exactly correct GeoJSON, but it's a bit surprising to say the least! I sort of thought the winding order fix would... not break it like that, and rather behave more like GeoJSON.io.
So, to address this, I tried running the geometry through the rewind module: https://github.com/chris48s/geojson-rewind. Here's the re-wound geometry:
{
"id": 1361026217,
"type": "Feature",
"properties": {},
"bbox": [41.661835, 27.536652, 41.701686, 27.556499],
"geometry": {
"coordinates": [
[
[41.701686, 27.555683],
[41.677091, 27.556499],
[41.674274, 27.555888],
[41.67182, 27.554058],
[41.667426, 27.54781 ],
[41.66299, 27.541284],
[41.661835, 27.538401],
[41.664217, 27.538102],
[41.665152, 27.538274],
[41.671067, 27.537625],
[41.671549, 27.538989],
[41.672853, 27.540324],
[41.674979, 27.541187],
[41.683195, 27.539543],
[41.684332, 27.538833],
[41.69456, 27.536652],
[41.694555, 27.537487],
[41.701676, 27.552681],
[41.701686, 27.555683],
[41.677091, 27.556499],
[41.701686, 27.555683]
]
],
"type": "Polygon"
}
}This does not raise any warnings when I paste it into geojson.io. However, if I put this geometry through antimeridian.fix_geojson, it still comes up with the inverted geometry and logs a winding warning 🤔 Even more confusing is that when I pass fix_winding=False, it still inverts the geometry (though it does not emit a warning)!