| 1 | """Alpha shape |
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| 2 | """ |
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| 3 | |
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| 4 | import exceptions |
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| 5 | from Numeric import array, Float, divide_safe, sqrt, product |
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| 6 | from load_mesh.loadASCII import load_points_file, export_boundary_file |
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| 7 | import random |
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| 8 | |
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| 9 | class PointError(exceptions.Exception): pass |
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| 10 | class FlagError(exceptions.Exception): pass |
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| 11 | |
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| 12 | OUTPUT_FILE_TITLE = "# The alpha shape boundary defined by point index pairs of edges" |
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| 13 | INF = pow(10,9) |
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| 14 | |
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| 15 | def alpha_shape_via_files(point_file, boundary_file, alpha= None): |
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| 16 | |
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| 17 | point_dict = load_points_file(point_file) |
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| 18 | points = point_dict['pointlist'] |
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| 19 | #title_string = point_dict['title'] |
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| 20 | |
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| 21 | alpha = Alpha_Shape(points) |
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| 22 | alpha.write_boundary(boundary_file) |
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| 23 | |
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| 24 | class Alpha_Shape: |
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| 25 | |
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| 26 | def __init__(self, points, alpha = None): |
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| 27 | |
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| 28 | """ |
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| 29 | Inputs: |
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| 30 | |
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| 31 | points: List of coordinate pairs [[x1, y1],[x2, y2]..] |
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| 32 | |
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| 33 | alpha: alpha shape parameter |
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| 34 | |
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| 35 | """ |
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| 36 | self._set_points(points) |
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| 37 | self._alpha_shape_algorithm(alpha) |
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| 38 | |
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| 39 | def _set_points(self, points): |
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| 40 | """ |
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| 41 | """ |
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| 42 | # print "setting points" |
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| 43 | if len (points) <= 2: |
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| 44 | raise PointError, "Too few points to find an alpha shape" |
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| 45 | if len(points)==3: |
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| 46 | #check not in a straight line |
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| 47 | x01 = points[0][0] - points[1][0] |
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| 48 | y01 = points[0][1] - points[1][1] |
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| 49 | x12 = points[1][0] - points[2][0] |
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| 50 | y12 = points[1][1] - points[2][1] |
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| 51 | crossprod = x01*y12 - x12*y01 |
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| 52 | if crossprod==0: |
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| 53 | raise PointError, "Three points on a straight line" |
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| 54 | |
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| 55 | #Convert input to Numeric arrays |
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| 56 | self.points = array(points).astype(Float) |
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| 57 | |
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| 58 | |
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| 59 | def write_boundary(self,file_name): |
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| 60 | """ |
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| 61 | Write the boundary to a file |
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| 62 | """ |
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| 63 | #print " this info will be in the file" |
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| 64 | export_boundary_file(file_name, self.get_boundary(), |
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| 65 | OUTPUT_FILE_TITLE, delimiter = ',') |
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| 66 | |
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| 67 | def get_boundary(self): |
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| 68 | """ |
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| 69 | """ |
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| 70 | return self.boundary |
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| 71 | |
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| 72 | def set_boundary_type(self,raw_boundary=True, |
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| 73 | remove_holes=False, |
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| 74 | smooth_indents=False, |
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| 75 | expand_pinch=False, |
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| 76 | boundary_points_fraction=0.2): |
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| 77 | """ |
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| 78 | Use the flags to set constraints on the boundary |
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| 79 | raw_boundary Return raw boundary i.e. the regular edges |
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| 80 | remove_holes filter to remove small holes |
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| 81 | smooth_indents remove sharp indents in boundary |
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| 82 | expand_pinch plus test for pinch-off |
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| 83 | i.e. boundary vertex with more than two edges. |
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| 84 | """ |
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| 85 | |
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| 86 | if raw_boundary: |
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| 87 | reg_edge = self.get_regular_edges(self.alpha) |
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| 88 | self.boundary = [self.edge[k] for k in reg_edge] |
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| 89 | self._init_boundary_triangles() |
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| 90 | if remove_holes: |
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| 91 | #remove holes |
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| 92 | self.boundary = self._remove_holes(boundary_points_fraction) |
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| 93 | if smooth_indents: |
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| 94 | #remove sharp indents |
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| 95 | self.boundary = self._smooth_indents() |
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| 96 | if expand_pinch: |
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| 97 | #deal with pinch-off |
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| 98 | self.boundary = self._expand_pinch() |
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| 99 | |
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| 100 | |
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| 101 | def get_delaunay(self): |
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| 102 | """ |
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| 103 | """ |
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| 104 | return self.deltri |
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| 105 | |
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| 106 | def get_optimum_alpha(self): |
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| 107 | """ |
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| 108 | """ |
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| 109 | return self.optimum_alpha |
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| 110 | |
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| 111 | def get_alpha(self): |
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| 112 | """ |
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| 113 | Return current alpha value |
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| 114 | """ |
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| 115 | return self.alpha |
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| 116 | |
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| 117 | def set_alpha(self,alpha): |
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| 118 | """ |
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| 119 | Set alpha and update alpha-boundary. |
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| 120 | """ |
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| 121 | self.alpha = alpha |
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| 122 | reg_edge = self.get_regular_edges(alpha) |
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| 123 | self.boundary = [self.edge[k] for k in reg_edge] |
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| 124 | self._init_boundary_triangles() |
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| 125 | |
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| 126 | |
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| 127 | def _alpha_shape_algorithm(self,alpha): |
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| 128 | |
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| 129 | # A python style guide suggests using _[function name] to |
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| 130 | # specify internal functions |
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| 131 | # - this is the first time I've used it though - DSG |
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| 132 | |
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| 133 | #print "starting alpha shape algorithm" |
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| 134 | |
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| 135 | self.alpha = alpha |
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| 136 | |
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| 137 | # Build Delaunay triangulation |
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| 138 | import triang |
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| 139 | points = [] |
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| 140 | seglist = [] |
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| 141 | holelist = [] |
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| 142 | regionlist = [] |
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| 143 | pointattlist = [] |
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| 144 | segattlist = [] |
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| 145 | trilist = [] |
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| 146 | |
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| 147 | points = [(pt[0], pt[1]) for pt in self.points] |
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| 148 | pointattlist = [ [] for i in range(len(points)) ] |
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| 149 | mode = "Qzcn" |
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| 150 | #print "computing delaunay triangulation ... \n" |
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| 151 | tridata = triang.genMesh(points,seglist,holelist,regionlist,pointattlist,segattlist,trilist,mode) |
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| 152 | #print tridata |
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| 153 | #print "point attribute list: ", tridata['generatedpointattributelist'],"\n" |
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| 154 | #print "hull segments: ", tridata['generatedsegmentlist'], "\n" |
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| 155 | self.deltri = tridata['generatedtrianglelist'] |
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| 156 | self.deltrinbr = tridata['generatedtriangleneighborlist'] |
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| 157 | self.hulledges = tridata['generatedsegmentlist'] |
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| 158 | |
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| 159 | #print "Number of delaunay triangles: ", len(self.deltri), "\n" |
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| 160 | #print "deltrinbrs: ", self.deltrinbr, "\n" |
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| 161 | |
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| 162 | # Build Alpha table |
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| 163 | # print "Building alpha table ... \n" |
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| 164 | self._tri_circumradius() |
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| 165 | # print "Largest circumradius ", max(self.triradius) |
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| 166 | self._edge_intervals() |
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| 167 | self._vertex_intervals() |
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| 168 | |
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| 169 | if alpha==None: |
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| 170 | # Find optimum alpha |
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| 171 | # Ken Clarkson's hull program uses smallest alpha so that |
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| 172 | # every vertex is non-singular so... |
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| 173 | self.optimum_alpha = max([ iv[0] for iv in self.vertexinterval if iv!=[] ]) |
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| 174 | # print "optimum alpha ", self.optimum_alpha |
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| 175 | self.alpha = self.optimum_alpha |
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| 176 | #alpha_tri = self.get_alpha_triangles(self.optimum_alpha) |
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| 177 | #print "alpha shape triangles ", alpha_tri |
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| 178 | |
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| 179 | reg_edge = self.get_regular_edges(self.optimum_alpha) |
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| 180 | #print "alpha boundary edges", reg_edge |
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| 181 | else: |
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| 182 | reg_edge = self.get_regular_edges(alpha) |
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| 183 | |
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| 184 | self.boundary = [self.edge[k] for k in reg_edge] |
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| 185 | #print "alpha boundary edges ", self.boundary |
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| 186 | self._init_boundary_triangles() |
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| 187 | |
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| 188 | return |
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| 189 | |
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| 190 | def _tri_circumradius(self): |
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| 191 | |
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| 192 | # compute circumradii of the delaunay triangles |
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| 193 | x = self.points[:,0] |
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| 194 | y = self.points[:,1] |
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| 195 | ind1 = [self.deltri[j][0] for j in range(len(self.deltri))] |
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| 196 | ind2 = [self.deltri[j][1] for j in range(len(self.deltri))] |
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| 197 | ind3 = [self.deltri[j][2] for j in range(len(self.deltri))] |
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| 198 | |
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| 199 | x1 = array([ x[j] for j in ind1 ]) |
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| 200 | y1 = array([ y[j] for j in ind1 ]) |
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| 201 | x2 = array([ x[j] for j in ind2 ]) |
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| 202 | y2 = array([ y[j] for j in ind2 ]) |
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| 203 | x3 = array([ x[j] for j in ind3 ]) |
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| 204 | y3 = array([ y[j] for j in ind3 ]) |
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| 205 | |
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| 206 | x21 = x2-x1 |
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| 207 | x31 = x3-x1 |
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| 208 | y21 = y2-y1 |
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| 209 | y31 = y3-y1 |
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| 210 | |
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| 211 | dist21 = x21*x21 + y21*y21 |
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| 212 | dist31 = x31*x31 + y31*y31 |
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| 213 | |
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| 214 | denom = x21*y31 - x31*y21 |
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| 215 | #print "denom = ", denom |
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| 216 | delta = 0.00000001 |
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| 217 | random.seed() |
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| 218 | zeroind = [k for k in range(len(denom)) if denom[k]==0 ] |
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| 219 | while zeroind!=[]: |
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| 220 | print "Warning: degenerate triangles found in alpha_shape.py, results may be inaccurate." |
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| 221 | for d in zeroind: |
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| 222 | x1[d] = x1[d]+delta*(random.random()-0.5) |
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| 223 | x2[d] = x2[d]+delta*(random.random()-0.5) |
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| 224 | x3[d] = x3[d]+delta*(random.random()-0.5) |
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| 225 | y1[d] = y1[d]+delta*(random.random()-0.5) |
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| 226 | y2[d] = y2[d]+delta*(random.random()-0.5) |
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| 227 | y3[d] = y3[d]+delta*(random.random()-0.5) |
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| 228 | x21 = x2-x1 |
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| 229 | x31 = x3-x1 |
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| 230 | y21 = y2-y1 |
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| 231 | y31 = y3-y1 |
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| 232 | dist21 = x21*x21 + y21*y21 |
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| 233 | dist31 = x31*x31 + y31*y31 |
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| 234 | denom = x21*y31 - x31*y21 |
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| 235 | zeroind = [k for k in range(len(denom)) if denom[k]==0 ] |
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| 236 | |
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| 237 | # dx/2, dy/2 give circumcenter relative to x1,y1. |
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| 238 | #dx = (y31*dist21 - y21*dist31)/denom |
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| 239 | #dy = (x21*dist31 - x31*dist21)/denom |
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| 240 | # from Numeric import divide_safe |
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| 241 | try: |
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| 242 | dx = divide_safe(y31*dist21 - y21*dist31,denom) |
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| 243 | dy = divide_safe(x21*dist31 - x31*dist21,denom) |
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| 244 | except ZeroDivisionError: |
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| 245 | print "There are serious problems with the delaunay triangles" |
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| 246 | raise |
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| 247 | |
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| 248 | |
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| 249 | self.triradius = 0.5*sqrt(dx*dx + dy*dy) |
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| 250 | #print "triangle radii", self.triradius |
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| 251 | return |
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| 252 | |
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| 253 | |
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| 254 | |
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| 255 | def _edge_intervals(self): |
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| 256 | # for each edge, find triples |
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| 257 | # (length/2, min_adj_triradius, max_adj_triradius) if unattached |
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| 258 | # (min_adj_triradius, min_adj_triradius, max_adj_triradius) if attached. |
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| 259 | |
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| 260 | # It should be possible to rewrite this routine in an array-friendly form |
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| 261 | # like _tri_circumradius() if we need to speed things up. |
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| 262 | |
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| 263 | edges = [] |
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| 264 | edgenbrs = [] |
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| 265 | edgeinterval = [] |
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| 266 | for t in range(len(self.deltri)): |
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| 267 | tri = self.deltri[t] |
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| 268 | trinbr = self.deltrinbr[t] |
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| 269 | dx = array([self.points[tri[(i+1)%3],0] - self.points[tri[(i+2)%3],0] for i in [0,1,2]]) |
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| 270 | dy = array([self.points[tri[(i+1)%3],1] - self.points[tri[(i+2)%3],1] for i in [0,1,2]]) |
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| 271 | elen = sqrt(dx*dx+dy*dy) |
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| 272 | #angle = array([(-dx[(i+1)%3]*dx[(i+2)%3]-dy[(i+1)%3]*dy[(i+2)%3])/(elen[(i+1)%3]*elen[(i+2)%3]) for i in [0,1,2]]) |
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| 273 | #angle = arccos(angle) |
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| 274 | # really only need sign - not angle value: |
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| 275 | anglesign = array([(-dx[(i+1)%3]*dx[(i+2)%3]-dy[(i+1)%3]*dy[(i+2)%3]) for i in [0,1,2]]) |
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| 276 | |
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| 277 | #print "dx ",dx,"\n" |
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| 278 | #print "dy ",dy,"\n" |
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| 279 | #print "edge lengths of triangle ",t,"\t",elen,"\n" |
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| 280 | #print "angles ",angle,"\n" |
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| 281 | |
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| 282 | for i in [0,1,2]: |
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| 283 | j = (i+1)%3 |
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| 284 | k = (i+2)%3 |
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| 285 | if trinbr[i]==-1: |
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| 286 | edges.append((tri[j], tri[k])) |
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| 287 | edgenbrs.append((t, -1)) |
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| 288 | edgeinterval.append([0.5*elen[i], self.triradius[t], INF]) |
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| 289 | elif (tri[j]<tri[k]): |
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| 290 | edges.append((tri[j], tri[k])) |
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| 291 | edgenbrs.append((t, trinbr[i])) |
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| 292 | edgeinterval.append([0.5*elen[i],\ |
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| 293 | min(self.triradius[t],self.triradius[trinbr[i]]),\ |
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| 294 | max(self.triradius[t],self.triradius[trinbr[i]]) ]) |
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| 295 | else: |
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| 296 | continue |
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| 297 | #if angle[i]>pi/2: |
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| 298 | if anglesign[i] < 0: |
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| 299 | edgeinterval[-1][0] = edgeinterval[-1][1] |
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| 300 | |
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| 301 | self.edge = edges |
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| 302 | self.edgenbr = edgenbrs |
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| 303 | self.edgeinterval = edgeinterval |
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| 304 | #print "edges: ",edges, "\n" |
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| 305 | #print "edge nbrs:", edgenbrs ,"\n" |
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| 306 | #print "edge intervals: ",edgeinterval , "\n" |
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| 307 | |
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| 308 | def _vertex_intervals(self): |
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| 309 | # for each vertex find pairs |
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| 310 | # (min_adj_triradius, max_adj_triradius) |
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| 311 | nv = len(self.points) |
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| 312 | vertexnbrs = [ [] for i in range(nv)] |
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| 313 | vertexinterval = [ [] for i in range(nv)] |
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| 314 | for t in range(len(self.deltri)): |
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| 315 | for j in self.deltri[t]: |
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| 316 | vertexnbrs[j].append(t) |
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| 317 | for h in range(len(self.hulledges)): |
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| 318 | for j in self.hulledges[h]: |
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| 319 | vertexnbrs[j].append(-1) |
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| 320 | |
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| 321 | for i in range(nv): |
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| 322 | radii = [ self.triradius[t] for t in vertexnbrs[i] if t>=0 ] |
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| 323 | try: |
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| 324 | vertexinterval[i] = [min(radii), max(radii)] |
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| 325 | if vertexnbrs[i][-1]==-1: |
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| 326 | vertexinterval[i][1]=INF |
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| 327 | except ValueError: |
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| 328 | # print "Vertex %i is isolated?"%i |
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| 329 | # print "coords: ",self.points[i] |
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| 330 | # print "Vertex nbrs: ", vertexnbrs[i] |
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| 331 | # print "nbr radii: ",radii |
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| 332 | # vertexinterval[i] = [0,INF] |
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| 333 | pass |
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| 334 | |
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| 335 | self.vertexnbr = vertexnbrs |
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| 336 | self.vertexinterval = vertexinterval |
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| 337 | #print "vertex nbrs ", vertexnbrs, "\n" |
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| 338 | #print "vertex intervals ",vertexinterval, "\n" |
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| 339 | |
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| 340 | def get_alpha_triangles(self,alpha): |
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| 341 | """ |
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| 342 | Given an alpha value, |
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| 343 | return indices of triangles in the alpha-shape |
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| 344 | """ |
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| 345 | def tri_rad_lta(k): |
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| 346 | return self.triradius[k]<=alpha |
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| 347 | |
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| 348 | return filter(tri_rad_lta, range(len(self.triradius))) |
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| 349 | |
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| 350 | def get_regular_edges(self,alpha): |
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| 351 | """ |
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| 352 | Given an alpha value, |
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| 353 | return the indices of edges on the boundary of the alpha-shape |
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| 354 | """ |
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| 355 | def reg_edge(k): |
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| 356 | return self.edgeinterval[k][1]<=alpha and self.edgeinterval[k][2]>alpha |
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| 357 | |
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| 358 | return filter(reg_edge, range(len(self.edgeinterval))) |
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| 359 | |
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| 360 | def get_exposed_vertices(self,alpha): |
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| 361 | """ |
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| 362 | Given an alpha value, |
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| 363 | return the vertices on the boundary of the alpha-shape |
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| 364 | """ |
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| 365 | def exp_vert(k): |
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| 366 | return self.vertexinterval[k][0]<=alpha and self.vertexinterval[k][1]>alpha |
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| 367 | |
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| 368 | return filter(exp_vert, range(len(self.vertexinterval))) |
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| 369 | |
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| 370 | def _vertices_from_edges(self,elist): |
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| 371 | """ |
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| 372 | Returns the list of unique vertex labels from edges in elist |
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| 373 | """ |
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| 374 | |
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| 375 | v1 = [elist[k][0] for k in range(len(elist))] |
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| 376 | v2 = [elist[k][1] for k in range(len(elist))] |
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| 377 | v = v1+v2 |
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| 378 | v.sort() |
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| 379 | vertices = [v[k] for k in range(len(v)) if v[k]!=v[k-1] ] |
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| 380 | return vertices |
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| 381 | |
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| 382 | def _init_boundary_triangles(self): |
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| 383 | """ |
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| 384 | Creates the initial list of triangle indices |
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| 385 | exterior to and touching the boundary of the alpha shape |
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| 386 | """ |
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| 387 | def tri_rad_gta(k): |
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| 388 | return self.triradius[k]>self.alpha |
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| 389 | |
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| 390 | extrind = filter(tri_rad_gta, range(len(self.triradius))) |
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| 391 | |
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| 392 | bv = self._vertices_from_edges(self.boundary) |
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| 393 | |
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| 394 | btri = [] |
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| 395 | for et in extrind: |
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| 396 | v0 = self.deltri[et][0] |
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| 397 | v1 = self.deltri[et][1] |
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| 398 | v2 = self.deltri[et][2] |
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| 399 | if v0 in bv or v1 in bv or v2 in bv: |
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| 400 | btri.append(et) |
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| 401 | |
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| 402 | self.boundarytriangle = btri |
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| 403 | |
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| 404 | #print "exterior triangles: ", extrind |
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| 405 | |
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| 406 | |
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| 407 | def _remove_holes(self,small): |
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| 408 | """ |
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| 409 | Given the edges in bdry, find the largest exterior components. |
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| 410 | """ |
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| 411 | |
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| 412 | #print "running _remove_holes \n" |
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| 413 | |
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| 414 | bdry = self.boundary |
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| 415 | |
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| 416 | def findroot(i): |
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| 417 | if vptr[i] < 0: |
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| 418 | return i |
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| 419 | k = findroot(vptr[i]) |
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| 420 | vptr[i] = k |
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| 421 | return k |
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| 422 | |
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| 423 | |
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| 424 | |
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| 425 | # get a list of unique vertex labels: |
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| 426 | verts = self._vertices_from_edges(bdry) |
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| 427 | #print "verts ", verts, "\n" |
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| 428 | |
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| 429 | #initialise vptr and eptr to negative number outside range |
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| 430 | EMPTY = -max(verts) - len(bdry) |
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| 431 | vptr = [EMPTY for k in range(len(verts))] |
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| 432 | eptr = [EMPTY for k in range(len(bdry))] |
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| 433 | #print "vptr init: ", vptr, "\n" |
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| 434 | |
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| 435 | #add edges and maintain union tree |
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| 436 | for i in range(len(bdry)): |
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| 437 | #print "edge ",i,"\t",bdry[i] |
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| 438 | vl = verts.index(bdry[i][0]) |
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| 439 | vr = verts.index(bdry[i][1]) |
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| 440 | #rvl = vl, rvr = vr |
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| 441 | rvl = findroot(vl) |
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| 442 | rvr = findroot(vr) |
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| 443 | #print "roots: ",rvl, rvr |
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| 444 | if not(rvl==rvr): |
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| 445 | if (vptr[vl]==EMPTY): |
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| 446 | if (vptr[vr]==EMPTY): |
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| 447 | vptr[vl] = -2 |
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| 448 | vptr[vr] = vl |
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| 449 | #eprt[i] = vl |
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| 450 | else: |
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| 451 | vptr[vl] = rvr |
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| 452 | vptr[rvr] -= 1 |
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| 453 | else: |
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| 454 | if (vptr[vr]==EMPTY): |
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| 455 | vptr[vr] = rvl |
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| 456 | vptr[rvl] -= 1 |
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| 457 | else: |
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| 458 | if vptr[rvl] > vptr[rvr]: |
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| 459 | vptr[rvr] += vptr[rvl] |
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| 460 | vptr[rvl] = rvr |
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| 461 | else: |
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| 462 | vptr[rvl] += vptr[rvr] |
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| 463 | vptr[rvr] = rvl |
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| 464 | #print "vptr: ", vptr, "\n" |
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| 465 | |
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| 466 | # end edge loop |
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| 467 | |
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| 468 | #print "vertex component tree: ", vptr, "\n" |
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| 469 | |
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| 470 | # discard the edges in the little components |
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| 471 | # (i.e. those components with less than 'small' fraction of bdry points) |
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| 472 | cutoff = round(small*len(verts)) |
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| 473 | littleind = [k for k in range(len(vptr)) if (vptr[k]<0 and vptr[k]>-cutoff)] |
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| 474 | if littleind: |
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| 475 | littlecomp = [k for k in range(len(vptr)) if findroot(k) in littleind] |
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| 476 | vdiscard = [verts[k] for k in littlecomp] |
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| 477 | newbdry = [e for e in bdry if not((e[0] in vdiscard) or (e[1] in vdiscard))] |
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| 478 | # remove boundary triangles that touch discarded components |
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| 479 | newbt = [] |
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| 480 | for bt in self.boundarytriangle: |
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| 481 | v0 = self.deltri[bt][0] |
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| 482 | v1 = self.deltri[bt][1] |
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| 483 | v2 = self.deltri[bt][2] |
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| 484 | if not (v0 in vdiscard or v1 in vdiscard or v2 in vdiscard): |
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| 485 | newbt.append(bt) |
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| 486 | self.boundarytriangle = newbt |
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| 487 | else: |
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| 488 | newbdry = bdry |
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| 489 | |
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| 490 | return newbdry |
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| 491 | |
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| 492 | |
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| 493 | def _smooth_indents(self): |
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| 494 | """ |
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| 495 | Given edges in bdry, test for acute-angle indents and remove them. |
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| 496 | """ |
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| 497 | |
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| 498 | #print "running _smooth_indents \n" |
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| 499 | |
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| 500 | bdry = self.boundary |
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| 501 | bdrytri = self.boundarytriangle |
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| 502 | verts = self._vertices_from_edges(bdry) |
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| 503 | |
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| 504 | # find boundary triangles that have two edges in bdry |
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| 505 | b2etri = [] |
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| 506 | for ind in bdrytri: |
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| 507 | bect = 0 |
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| 508 | for j in [0,1,2]: |
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| 509 | eda = (self.deltri[ind][(j+1)%3], self.deltri[ind][(j+2)%3]) |
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| 510 | edb = (self.deltri[ind][(j+2)%3], self.deltri[ind][(j+1)%3]) |
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| 511 | if eda in bdry or edb in bdry: |
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| 512 | bect +=1 |
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| 513 | if bect==2: |
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| 514 | b2etri.append(ind) |
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| 515 | |
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| 516 | # test the bdrytri triangles for acute angles |
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| 517 | acutetri = [] |
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| 518 | for tind in b2etri: |
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| 519 | tri = self.deltri[tind] |
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| 520 | dx = array([self.points[tri[(i+1)%3],0] - self.points[tri[(i+2)%3],0] for i in [0,1,2]]) |
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| 521 | dy = array([self.points[tri[(i+1)%3],1] - self.points[tri[(i+2)%3],1] for i in [0,1,2]]) |
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| 522 | anglesign = array([(-dx[(i+1)%3]*dx[(i+2)%3]-dy[(i+1)%3]*dy[(i+2)%3]) for i in [0,1,2]]) |
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| 523 | if product(anglesign) > 0: |
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| 524 | acutetri.append(tind) |
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| 525 | |
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| 526 | #print "acute boundary triangles ", acutetri |
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| 527 | |
|---|
| 528 | # adjust the bdry edges and triangles by adding in the acutetri triangles |
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| 529 | for pind in acutetri: |
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| 530 | bdrytri.remove(pind) |
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| 531 | tri = self.deltri[pind] |
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| 532 | for i in [0,1,2]: |
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| 533 | bdry.append((tri[(i+1)%3], tri[(i+2)%3])) |
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| 534 | |
|---|
| 535 | self.boundarytriangle = bdrytri |
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| 536 | |
|---|
| 537 | newbdry = [] |
|---|
| 538 | for ed in bdry: |
|---|
| 539 | numed = bdry.count(ed)+bdry.count((ed[1],ed[0])) |
|---|
| 540 | if numed%2 == 1: |
|---|
| 541 | newbdry.append(ed) |
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| 542 | |
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| 543 | #print "new boundary ", newbdry |
|---|
| 544 | return newbdry |
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| 545 | |
|---|
| 546 | def _expand_pinch(self): |
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| 547 | """ |
|---|
| 548 | Given edges in bdry, test for vertices with more than 2 incident edges. |
|---|
| 549 | Expand by adding back in associated triangles... |
|---|
| 550 | """ |
|---|
| 551 | #print "running _expand_pinch \n" |
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| 552 | |
|---|
| 553 | bdry = self.boundary |
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| 554 | bdrytri = self.boundarytriangle |
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| 555 | |
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| 556 | v1 = [bdry[k][0] for k in range(len(bdry))] |
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| 557 | v2 = [bdry[k][1] for k in range(len(bdry))] |
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| 558 | v = v1+v2 |
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| 559 | v.sort() |
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| 560 | probv = [v[k] for k in range(len(v)) if (v[k]!=v[k-1] and v.count(v[k])>2) ] |
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| 561 | #print "problem vertices: ", probv |
|---|
| 562 | |
|---|
| 563 | # find boundary triangles that have at least one vertex in probv |
|---|
| 564 | probtri = [] |
|---|
| 565 | for ind in bdrytri: |
|---|
| 566 | v0 = self.deltri[ind][0] |
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| 567 | v1 = self.deltri[ind][1] |
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| 568 | v2 = self.deltri[ind][2] |
|---|
| 569 | if v0 in probv or v1 in probv or v2 in probv: |
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| 570 | probtri.append(ind) |
|---|
| 571 | |
|---|
| 572 | #print "problem boundary triangle indices ", probtri |
|---|
| 573 | |
|---|
| 574 | # "add in" the problem triangles |
|---|
| 575 | for pind in probtri: |
|---|
| 576 | bdrytri.remove(pind) |
|---|
| 577 | tri = self.deltri[pind] |
|---|
| 578 | for i in [0,1,2]: |
|---|
| 579 | bdry.append((tri[(i+1)%3], tri[(i+2)%3])) |
|---|
| 580 | |
|---|
| 581 | self.boundarytriangle = bdrytri |
|---|
| 582 | |
|---|
| 583 | newbdry = [] |
|---|
| 584 | for ed in bdry: |
|---|
| 585 | numed = bdry.count(ed)+bdry.count((ed[1],ed[0])) |
|---|
| 586 | if numed%2 == 1: |
|---|
| 587 | newbdry.append(ed) |
|---|
| 588 | |
|---|
| 589 | #print "new boundary ", newbdry |
|---|
| 590 | return newbdry |
|---|
| 591 | |
|---|
| 592 | |
|---|
| 593 | #------------------------------------------------------------- |
|---|
| 594 | if __name__ == "__main__": |
|---|
| 595 | """ |
|---|
| 596 | Load in a data point file. |
|---|
| 597 | Determine the alpha shape boundary |
|---|
| 598 | Save the boundary to a file. |
|---|
| 599 | |
|---|
| 600 | usage: alpha_shape.py point_file.xya boundary_file.bnd [alpha] |
|---|
| 601 | |
|---|
| 602 | The alpha value is optional. |
|---|
| 603 | """ |
|---|
| 604 | |
|---|
| 605 | import os, sys |
|---|
| 606 | usage = "usage: %s point_file.xya boundary_file.bnd [alpha]"%os.path.basename(sys.argv[0]) |
|---|
| 607 | # I made up the .bnd affix. Other ideas welcome. -DSG |
|---|
| 608 | if len(sys.argv) < 3: |
|---|
| 609 | print usage |
|---|
| 610 | else: |
|---|
| 611 | point_file = sys.argv[1] |
|---|
| 612 | boundary_file = sys.argv[2] |
|---|
| 613 | if len(sys.argv) > 4: |
|---|
| 614 | alpha = sys.argv[3] |
|---|
| 615 | else: |
|---|
| 616 | alpha = None |
|---|
| 617 | |
|---|
| 618 | #print "about to call alpha shape routine \n" |
|---|
| 619 | alpha_shape_via_files(point_file, boundary_file, alpha) |
|---|
| 620 | |
|---|
