Loop.Intersects gives incorrect results #51
Comments
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Both of the loops are invalid because they have duplicate vertices. The
duplicate vertex leads to undefined results in most of the resulting
calculations.
l1.Validate() = edge 4 is degenerate (duplicate vertex)
l2.Validate() = edge 6 is degenerate (duplicate vertex)
…On Tue, May 21, 2019 at 5:12 PM Yanhe Chen ***@***.***> wrote:
I have two geojson objects
Polygon 1:
[[[-74.93335056304832,39.283340980346445],
[-74.93335056305031,40.30000217770297],
[-75.91667795181374,40.30000217770097],
[-75.91667795181175,40.28334098034444],
[-74.93335056304832,39.283340980346445]]]
Polygon 2:
[[[-74.3122237229173, 39.9541747627284],
[-74.1955570274039, 40.0833414585103],
[-74.5497238128233, 40.1958414684098],
[-74.7163905245327, 40.0583414352459],
[-74.8663905578957, 39.8208413826612],
[-74.4163904122584,39.7708413884741],
[-74.3122237229173, 39.9541747627284]]]
I converted [][][]float64 array to Loop using Function:
func convertFloatListToPolygon(floatList [][][]float64) *s2.Loop {
points := floatList[0]
pointList := make([]s2.Point, 0)
for _, point := range points {
s2Point := s2.PointFromLatLng(
s2.LatLng{
Lat:s1.Angle(point[1]),
Lng:s1.Angle(point[0]),
})
pointList = append(pointList, s2Point)
}
return s2.LoopFromPoints(pointList)
}
poly = convertFloatListToPolygon(p1)
comparedPoly = convertFloatListToPolygon(p2)
poly.Intersects(comparedPoly)
The results is true. However, when I draw those two polygon in geojson.io,
it's not intersected.
Could someone tell me if I use function wrong or there is a bug in
intersection?
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@rsned Thanks for answering. Is there an efficient way to make a valid loop then? |
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Looking at the GeoJSON spec, the duplicate vertex seems to be part of the
specification, so I would say in your convert function you skip the last
element when converting to points to use for an s2.Loop
o A linear ring is a closed LineString with four or more positions.
o The first and last positions are equivalent, and they MUST contain
identical values; their representation SHOULD also be identical.
Do you know what version of the GeoJSON these loops are coming from? Older
versions were not required to output points in right-hand rule order. The
points you list are in clockwise order, and s2.Loop assumes
counter-clockwise. So what you are getting is actually 2 loops that
encompass 99.99% of the surface of the earth instead of two small loops.
If you print the RectBound for the loops, you will see that the loops as
created end up with a full Rect:
bound:{Lat:{Lo:-1.5707963267948966 Hi:1.5707963267948966}
Lng:{Lo:-3.141592653589793 Hi:3.141592653589793}}
Lat: -pi/2 (-90) - +pi (90) ,
Lng: -pi (-180) - pi (180)
If the points are reversed to be counter-clockwise order, the bounds now
are fairly tight around the shape: e.g.,
bound:{Lat:{Lo:-1.3066650143192748 Hi:-1.294956760479414}
Lng:{Lo:0.6941321285173062 Hi:0.7015497792334233}}
Lat: -74.8663906 - -74.195557
Lng: 39.770841388572755 - 40.1958414685095135
You will probably want to call Normalize() on the loops which will invert
them if they cover more than half the sphere.
l1.Normalize()
l2.Normalize()
l1.Intersects(l2) == false now
- Robert
…On Wed, May 22, 2019 at 11:02 AM Yanhe Chen ***@***.***> wrote:
@rsned <https://github.com/rsned> Thanks for answering. Is there an
efficient way to make a valid loop then?
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@rsned Thanks for the clarification. However, if the point data is On the map, those two are not intersects. I removed the last one and it has been validate. Then normalize them. However, they are still considering intersecting. |
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@rsned The rectbound is : |
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Some other examples also fails, such as I construct a Polygon using Rectangle Points: and then another points is: After validate and normalize, those two shows that have intersections. |
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s1,Angle's are in radians not degrees, so your values are all greater then
2*pi. You need to multiply the s1.Angle by s1.Degree to get them, in the
right range.
…On Wed, May 22, 2019 at 4:43 PM Yanhe Chen ***@***.***> wrote:
Some other examples also fails, such as I construct a Polygon using
Rectangle Points:
minLat: 30,
maxLat: 31,
minLng: -71,
maxLng: -70
func convertRectangleToPolygon(rectangle *models.Rectangle) s2.Loop {
var Vertices []s2.Point
Vertices = append(Vertices, s2.PointFromLatLng(s2.LatLng{s1.Angle(*rectangle.MinLat), s1.Angle(*rectangle.MaxLng)}))
Vertices = append(Vertices, s2.PointFromLatLng(s2.LatLng{s1.Angle(*rectangle.MaxLat), s1.Angle(*rectangle.MaxLng)}))
Vertices = append(Vertices, s2.PointFromLatLng(s2.LatLng{s1.Angle(*rectangle.MaxLat), s1.Angle(*rectangle.MinLng)}))
Vertices = append(Vertices, s2.PointFromLatLng(s2.LatLng{s1.Angle(*rectangle.MinLat), s1.Angle(*rectangle.MinLng)}))
loop := *s2.LoopFromPoints(Vertices)
return loop
}
and then another points is:
[[[-142.848733550224,65.2780581505263 ,0],
[-142.869406610785,65.2816692577486 ,0],
[-142.906606068389,65.2936136946703 ,0],
[-142.933446911371 ,65.3013914676046 ,0],
[-142.954876639064 ,65.3061136856359 ,0],
[-142.972775531381 ,65.3086136823949 ,0],
[-142.984559699584 ,65.3102803472599 ,0],
[-142.992692481551 ,65.3138914566595 ,0],
[-142.999557204145 ,65.3141692334514 ,0] ,
[-143.002526371116 ,65.3140025659437 ,0],
[-143.002526234783 ,65.1760859060438 ,0] ,
[-142.992948458279 ,65.1780581306049 ,0] ,
[-142.977845128404 ,65.1819470210269 ,0] ,
[-142.964788184438 ,65.1836136902078 ,0] ,
[-142.92530207324 ,65.1852803639764 ,0] ,
[-142.913760407519 ,65.1861136989371 ,0] ,
[-142.907678742146 ,65.1880581448932 ,0] ,
[-142.894071246426 ,65.1930581469995 ,0] ,
[-142.875424585382 ,65.2000025938815 ,0] ,
[-142.858695982345 ,65.2088914853316 ,0] ,
[-142.850253488789 ,65.2158359304428 ,0],
[-142.847262661947 ,65.2222248196358 ,0],
[-142.847331559995 ,65.2313914861557 ,0],
[-142.843687676307 ,65.2369470415047 ,0],
[-142.822621298931, 65.2497248225114 ,0],
[-142.812817971782 ,65.2561137128883 ,0],
[-142.814827977926 ,65.2622248232271 ,0] ,
[-142.817098260534 ,65.2677803785489 ,0] ,
[-142.813569930943, 65.2713914899776, 0] ,
[-142.813032435321 ,65.275835933844 ,0] ,
[-142.817096326717 ,65.2780581560244 ,0] ,
[-142.826978270638 ,65.2775025983354 ,0],
[-142.848733550224 ,65.2780581505263 ,0]]]
After validate and normalize, those two shows that have intersections.
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@rsned That really solved my problems. Haven't notice the part that angle is in radians.... |
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I have two geojson objects
Polygon 1:
[[[-74.93335056304832,39.283340980346445],
[-74.93335056305031,40.30000217770297],
[-75.91667795181374,40.30000217770097],
[-75.91667795181175,40.28334098034444],
[-74.93335056304832,39.283340980346445]]]
Polygon 2:
[[[-74.3122237229173, 39.9541747627284],
[-74.1955570274039, 40.0833414585103],
[-74.5497238128233, 40.1958414684098],
[-74.7163905245327, 40.0583414352459],
[-74.8663905578957, 39.8208413826612],
[-74.4163904122584,39.7708413884741],
[-74.3122237229173, 39.9541747627284]]]
I converted [][][]float64 array to Loop using Function:
func convertFloatListToPolygon(floatList [][][]float64) *s2.Loop {points := floatList[0]pointList := make([]s2.Point, 0)for _, point := range points {s2Point := s2.PointFromLatLng(s2.LatLng{Lat:s1.Angle(point[1]),Lng:s1.Angle(point[0]),poly = convertFloatListToPolygon(p1)comparedPoly = convertFloatListToPolygon(p2)poly.Intersects(comparedPoly)The results is true. However, when I draw those two polygon in geojson.io, it's not intersected.
Could someone tell me if I use function wrong or there is a bug in intersection?
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