How to filter a triangle list with a mask

Filter triangulation.ipynb

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  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import menpo\n",
      "import numpy as np"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "trilist = np.array([0, 1, 2, 0, 3, 2, 2, 5, 4, 4, 5, 6]).reshape([4, 3])\n",
      "points = np.random.rand(7, 3)\n",
      "mask = np.array([True, False, True, True, True, True, True])"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print points"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "[[ 0.81988993  0.71700209  0.50835648]\n",
        " [ 0.79093236  0.36038279  0.84154055]\n",
        " [ 0.22104768  0.03970721  0.4352194 ]\n",
        " [ 0.25306475  0.81060459  0.05632058]\n",
        " [ 0.00627229  0.03531831  0.72232639]\n",
        " [ 0.27690353  0.82088957  0.90024519]\n",
        " [ 0.34770358  0.62584806  0.22801873]]\n"
       ]
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print trilist"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "[[0 1 2]\n",
        " [0 3 2]\n",
        " [2 5 4]\n",
        " [4 5 6]]\n"
       ]
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# What point indices are left?\n",
      "i = np.arange(points.shape[0])\n",
      "i_left = i[mask]"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 5
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# filter triangles removing any that contain a missing point.\n",
      "tri_kept_mask = ~np.any(~np.in1d(trilist, i_left).reshape(trilist.shape), axis=1)\n",
      "tri_kept = trilist[tri_kept_mask]\n",
      "# only remaining indices in tri_kept survive\n",
      "i_kept = np.sort(np.unique(tri_kept))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 6
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# need to re-index. Build a new index\n",
      "i_new = np.arange(i_kept.size)\n",
      "# i_to_new[i] = i_new\n",
      "i_to_new = i.copy()\n",
      "i_to_new[i_kept] = i_new"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 7
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# use i_to_new, tri_kept to build new trilist and points\n",
      "new_trilist = i_to_new[tri_kept.ravel()].reshape([-1, 3])\n",
      "new_points = points[i_kept]"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 8
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print new_trilist"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "[[0 2 1]\n",
        " [1 4 3]\n",
        " [3 4 5]]\n"
       ]
      }
     ],
     "prompt_number": 9
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print new_points"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "[[ 0.81988993  0.71700209  0.50835648]\n",
        " [ 0.22104768  0.03970721  0.4352194 ]\n",
        " [ 0.25306475  0.81060459  0.05632058]\n",
        " [ 0.00627229  0.03531831  0.72232639]\n",
        " [ 0.27690353  0.82088957  0.90024519]\n",
        " [ 0.34770358  0.62584806  0.22801873]]\n"
       ]
      }
     ],
     "prompt_number": 10
    }
   ],
   "metadata": {}
  }
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