Method initBound

s2/loop.go:175–216

initBound sets up the approximate bounding Rects for this loop.

()

// initBound sets up the approximate bounding Rects for this loop.
func (l *Loop) initBound() {
	if len(l.vertices) == 0 {
		*l = *EmptyLoop()
		return
	}
	// Check for the special "empty" and "full" loops.
	if l.isEmptyOrFull() {
		if l.IsEmpty() {
			l.bound = EmptyRect()
		} else {
			l.bound = FullRect()
		}
		l.subregionBound = l.bound
		return
	}

	// The bounding rectangle of a loop is not necessarily the same as the
	// bounding rectangle of its vertices. First, the maximal latitude may be
	// attained along the interior of an edge. Second, the loop may wrap
	// entirely around the sphere (e.g. a loop that defines two revolutions of a
	// candy-cane stripe). Third, the loop may include one or both poles.
	// Note that a small clockwise loop near the equator contains both poles.
	bounder := NewRectBounder()
	for i := 0; i <= len(l.vertices); i++ { // add vertex 0 twice
		bounder.AddPoint(l.Vertex(i))
	}
	b := bounder.RectBound()

	if l.ContainsPoint(Point{r3.Vector{X: 0, Y: 0, Z: 1}}) {
		b = Rect{r1.Interval{Lo: b.Lat.Lo, Hi: math.Pi / 2}, s1.FullInterval()}
	}
	// If a loop contains the south pole, then either it wraps entirely
	// around the sphere (full longitude range), or it also contains the
	// north pole in which case b.Lng.IsFull() due to the test above.
	// Either way, we only need to do the south pole containment test if
	// b.Lng.IsFull().
	if b.Lng.IsFull() && l.ContainsPoint(Point{r3.Vector{X: 0, Y: 0, Z: -1}}) {
		b.Lat.Lo = -math.Pi / 2
	}
	l.bound = b
	l.subregionBound = ExpandForSubregions(l.bound)
}

// Validate checks whether this is a valid loop.
func (l *Loop) Validate() error {