point-in-big-polygon/pnp-big.js

Industrial strength point in polygon test

module.exports = preprocessPolygon

var orient = require('robust-orientation')[3]
var makeSlabs = require('slab-decomposition')
var makeIntervalTree = require('interval-tree-1d')
var bsearch = require('binary-search-bounds')

function visitInterval() {
  return true
}

function intervalSearch(table) {
  return function(x, y) {
    var tree = table[x]
    if(tree) {
      return !!tree.queryPoint(y, visitInterval)
    }
    return false
  }
}

function buildVerticalIndex(segments) {
  var table = {}
  for(var i=0; i<segments.length; ++i) {
    var s = segments[i]
    var x = s[0][0]
    var y0 = s[0][1]
    var y1 = s[1][1]
    var p = [ Math.min(y0, y1), Math.max(y0, y1) ]
    if(x in table) {
      table[x].push(p)
    } else {
      table[x] = [ p ]
    }
  }
  var intervalTable = {}
  var keys = Object.keys(table)
  for(var i=0; i<keys.length; ++i) {
    var segs = table[keys[i]]
    intervalTable[keys[i]] = makeIntervalTree(segs)
  }
  return intervalSearch(intervalTable)
}

function buildSlabSearch(slabs, coordinates) {
  return function(p) {
    var bucket = bsearch.le(coordinates, p[0])
    if(bucket < 0) {
      return 1
    }
    var root = slabs[bucket]
    if(!root) {
      if(bucket > 0 && coordinates[bucket] === p[0]) {
        root = slabs[bucket-1]
      } else {
        return 1
      }
    }
    var lastOrientation = 1
    while(root) {
      var s = root.key
      var o = orient(p, s[0], s[1])
      if(s[0][0] < s[1][0]) {
        if(o < 0) {
          root = root.left
        } else if(o > 0) {
          lastOrientation = -1
          root = root.right
        } else {
          return 0
        }
      } else {
        if(o > 0) {
          root = root.left
        } else if(o < 0) {
          lastOrientation = 1
          root = root.right
        } else {
          return 0
        }
      }
    }
    return lastOrientation
  }
}

function classifyEmpty(p) {
  return 1
}

function createClassifyVertical(testVertical) {
  return function classify(p) {
    if(testVertical(p[0], p[1])) {
      return 0
    }
    return 1
  }
}

function createClassifyPointDegen(testVertical, testNormal) {
  return function classify(p) {
    if(testVertical(p[0], p[1])) {
      return 0
    }
    return testNormal(p)
  }
}

function preprocessPolygon(loops) {
  //Compute number of loops
  var numLoops = loops.length

  //Unpack segments
  var segments = []
  var vsegments = []
  var ptr = 0
  for(var i=0; i<numLoops; ++i) {
    var loop = loops[i]
    var numVertices = loop.length
    for(var s=numVertices-1,t=0; t<numVertices; s=(t++)) {
      var a = loop[s]
      var b = loop[t]
      if(a[0] === b[0]) {
        vsegments.push([a,b])
      } else {
        segments.push([a,b])
      }
    }
  }

  //Degenerate case: All loops are empty
  if(segments.length === 0) {
    if(vsegments.length === 0) {
      return classifyEmpty
    } else {
      return createClassifyVertical(buildVerticalIndex(vsegments))
    }
  }

  //Build slab decomposition
  var slabs = makeSlabs(segments)
  var testSlab = buildSlabSearch(slabs.slabs, slabs.coordinates)

  if(vsegments.length === 0) {
    return testSlab
  } else {
    return createClassifyPointDegen(
      buildVerticalIndex(vsegments),
      testSlab)
  }
}