code: function getTJunctions (points, edges, edgeBounds, vertBounds) {
    var result = []
    boxIntersect(edgeBounds, vertBounds, function (i, v) {
      var e = edges[i]
      if (e[0] === v || e[1] === v) {
        return
      }
      var p = points[v]
      var a = points[e[0]]
      var b = points[e[1]]
      if (segseg(a, b, p, p)) {
        result.push([i, v])
      }
    })
    return result
  }
docs: Find all pairs of crossing vertices in a pslg (given edge/vert bounds)