Add Polygon centroid and center of mass #148
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1ec5
added
improvement
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Thank you for porting the JavaScript implementation of these methods – I’m sure a lot of developers will find them quite handy. I haven’t gone line by line comparing the port to the original JavaScript, but let me know if you’d like a second pair of eyes on that.
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| var signedArea: Double = 0 | ||
| var sum = LocationCoordinate2D(latitude: 0, longitude: 0) | ||
| let zipped = zip(neutralized.prefix(upTo: neutralized.count - 1), neutralized.suffix(from: 1)) |
| /// Calculates the centroid using the mean of all vertices. | ||
| /// This lessens the effect of small islands and artifacts when calculating the centroid of a set of polygons. | ||
| public func centroid() -> LocationCoordinate2D? { | ||
| let coordinates = outerRing.coordinates.dropLast() |
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In the future, once similar calculations are implemented for other geometry types, Geometry itself could have centroid and centerOfMass properties that pass through to type-specific implementations like this.
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@nighthawk, not to rush you, but feel free to push up a revised version when you’re ready, or let us know if you need help. FYI, we’re planning to release v2.0.0 in the coming weeks, but these changes are backwards-compatible, so we can land them in a subsequent minor version if the timing works out better. |
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@1ec5 , no worries. I've pushed a revised version. Please have a look. A little curiosity that I encountered when implementing |
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| func testPolygonCentre() { | ||
| // Adopted from https://github.com/Turfjs/turf/blob/3b20c568e5638f680cde39c26b56fbcf034133f2/packages/turf-center/test.js | ||
| let coordinate = LocationCoordinate2D(latitude: 45.7536760235992, longitude: 4.841880798339844) |
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I suppose the Lyon example would be more offset than expected when using mid(_:_:) because of a longstanding issue in which LocationCoordinate2D.distance(to:) uses a different approximation of the radius of the Earth than Turf.js does these days: #26.
This ports Turf's
centerOfMassandcentroidto Swift, at least for the individualPolygoncase. I've followed the same implementation and test cases as from the JS repo.Note: This could be extended to support the other geometries that Turf.js supports, though this should then also add support for convex hull calculations.
This addresses part of #145.