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54 lines
1.9 KiB
Go
54 lines
1.9 KiB
Go
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// Copyright 2018 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package s2
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// This file defines various measures for polylines on the sphere. These are
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// low-level methods that work directly with arrays of Points. They are used to
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// implement the methods in various other measures files.
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import (
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"github.com/golang/geo/r3"
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"github.com/golang/geo/s1"
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)
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// polylineLength returns the length of the given Polyline.
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// It returns 0 for polylines with fewer than two vertices.
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func polylineLength(p []Point) s1.Angle {
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var length s1.Angle
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for i := 1; i < len(p); i++ {
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length += p[i-1].Distance(p[i])
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}
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return length
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}
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// polylineCentroid returns the true centroid of the polyline multiplied by the
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// length of the polyline. The result is not unit length, so you may wish to
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// normalize it.
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//
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// Scaling by the Polyline length makes it easy to compute the centroid
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// of several Polylines (by simply adding up their centroids).
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//
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// Note that for degenerate Polylines (e.g., AA) this returns Point(0, 0, 0).
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// (This answer is correct; the result of this function is a line integral over
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// the polyline, whose value is always zero if the polyline is degenerate.)
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func polylineCentroid(p []Point) Point {
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var centroid r3.Vector
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for i := 1; i < len(p); i++ {
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centroid = centroid.Add(EdgeTrueCentroid(p[i-1], p[i]).Vector)
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}
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return Point{centroid}
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}
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