Mercurial > gemma
annotate pkg/octree/hull.go @ 3465:3c13a6f2227b
afd(LNWL): additional queryparams (widthbreaks, depthbreaks) for sections and stretches implemented
author | Thomas Junk <thomas.junk@intevation.de> |
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date | Mon, 27 May 2019 10:38:42 +0200 |
parents | 620038ade708 |
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rev | line source |
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620038ade708
Incorporated fogleman's fast Delaunay triangulation adjuted to our vertex model.
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1 // Copyright (C) 2018 Michael Fogleman |
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2 // |
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3 // Permission is hereby granted, free of charge, to any person obtaining |
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4 // a copy of this software and associated documentation files (the "Software"), |
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5 // to deal in the Software without restriction, including without limitation |
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6 // the rights to use, copy, modify, merge, publish, distribute, sublicense, |
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7 // and/or sell copies of the Software, and to permit persons to whom the |
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8 // Software is furnished to do so, subject to the following conditions: |
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9 // |
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10 // The above copyright notice and this permission notice shall be included |
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11 // in all copies or substantial portions of the Software. |
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12 // |
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13 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS |
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14 // OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
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15 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL |
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16 // THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
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17 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, |
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18 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. |
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19 |
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20 package octree |
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21 |
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22 import "sort" |
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23 |
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24 func cross2D(p, a, b Vertex) float64 { |
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25 return (a.X-p.X)*(b.Y-p.Y) - (a.Y-p.Y)*(b.X-p.X) |
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26 } |
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27 |
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28 // ConvexHull returns the convex hull of the provided points. |
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29 func ConvexHull(points []Vertex) []Vertex { |
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30 // copy points |
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31 pointsCopy := make([]Vertex, len(points)) |
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32 copy(pointsCopy, points) |
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33 points = pointsCopy |
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34 |
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35 // sort points |
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36 sort.Slice(points, func(i, j int) bool { |
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37 a := points[i] |
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38 b := points[j] |
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39 if a.X != b.X { |
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40 return a.X < b.X |
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41 } |
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42 return a.Y < b.Y |
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43 }) |
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44 |
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45 // filter nearly-duplicate points |
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46 distinctPoints := points[:0] |
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47 for i, p := range points { |
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48 if i > 0 && p.SquaredDistance2D(points[i-1]) < eps { |
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49 continue |
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50 } |
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51 distinctPoints = append(distinctPoints, p) |
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52 } |
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53 points = distinctPoints |
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54 |
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55 // find upper and lower portions |
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56 var U, L []Vertex |
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57 for _, p := range points { |
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58 for len(U) > 1 && cross2D(U[len(U)-2], U[len(U)-1], p) > 0 { |
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59 U = U[:len(U)-1] |
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60 } |
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61 for len(L) > 1 && cross2D(L[len(L)-2], L[len(L)-1], p) < 0 { |
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62 L = L[:len(L)-1] |
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63 } |
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64 U = append(U, p) |
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65 L = append(L, p) |
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66 } |
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67 |
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68 // reverse upper portion |
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69 for i, j := 0, len(U)-1; i < j; i, j = i+1, j-1 { |
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70 U[i], U[j] = U[j], U[i] |
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71 } |
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72 |
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73 // construct complete hull |
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74 if len(U) > 0 { |
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75 U = U[:len(U)-1] |
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76 } |
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77 if len(L) > 0 { |
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78 L = L[:len(L)-1] |
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79 } |
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80 return append(L, U...) |
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81 } |