[chore] add back exif-terminator and use only for jpeg,png,webp (#3161)

* add back exif-terminator and use only for jpeg,png,webp

* fix arguments passed to terminateExif()

* pull in latest exif-terminator

* fix test

* update processed img

---------

Co-authored-by: tobi <tobi.smethurst@protonmail.com>

1 files changed, 698 insertions, 0 deletions

diff --git a/vendor/github.com/golang/geo/s2/cell.go b/vendor/github.com/golang/geo/s2/cell.go
new file mode 100644
index 000000000..0a01a4f1f
--- /dev/null
+++ b/vendor/github.com/golang/geo/s2/cell.go
@@ -0,0 +1,698 @@
+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package s2
+
+import (
+	"io"
+	"math"
+
+	"github.com/golang/geo/r1"
+	"github.com/golang/geo/r2"
+	"github.com/golang/geo/r3"
+	"github.com/golang/geo/s1"
+)
+
+// Cell is an S2 region object that represents a cell. Unlike CellIDs,
+// it supports efficient containment and intersection tests. However, it is
+// also a more expensive representation.
+type Cell struct {
+	face        int8
+	level       int8
+	orientation int8
+	id          CellID
+	uv          r2.Rect
+}
+
+// CellFromCellID constructs a Cell corresponding to the given CellID.
+func CellFromCellID(id CellID) Cell {
+	c := Cell{}
+	c.id = id
+	f, i, j, o := c.id.faceIJOrientation()
+	c.face = int8(f)
+	c.level = int8(c.id.Level())
+	c.orientation = int8(o)
+	c.uv = ijLevelToBoundUV(i, j, int(c.level))
+	return c
+}
+
+// CellFromPoint constructs a cell for the given Point.
+func CellFromPoint(p Point) Cell {
+	return CellFromCellID(cellIDFromPoint(p))
+}
+
+// CellFromLatLng constructs a cell for the given LatLng.
+func CellFromLatLng(ll LatLng) Cell {
+	return CellFromCellID(CellIDFromLatLng(ll))
+}
+
+// Face returns the face this cell is on.
+func (c Cell) Face() int {
+	return int(c.face)
+}
+
+// oppositeFace returns the face opposite the given face.
+func oppositeFace(face int) int {
+	return (face + 3) % 6
+}
+
+// Level returns the level of this cell.
+func (c Cell) Level() int {
+	return int(c.level)
+}
+
+// ID returns the CellID this cell represents.
+func (c Cell) ID() CellID {
+	return c.id
+}
+
+// IsLeaf returns whether this Cell is a leaf or not.
+func (c Cell) IsLeaf() bool {
+	return c.level == maxLevel
+}
+
+// SizeIJ returns the edge length of this cell in (i,j)-space.
+func (c Cell) SizeIJ() int {
+	return sizeIJ(int(c.level))
+}
+
+// SizeST returns the edge length of this cell in (s,t)-space.
+func (c Cell) SizeST() float64 {
+	return c.id.sizeST(int(c.level))
+}
+
+// Vertex returns the k-th vertex of the cell (k = 0,1,2,3) in CCW order
+// (lower left, lower right, upper right, upper left in the UV plane).
+func (c Cell) Vertex(k int) Point {
+	return Point{faceUVToXYZ(int(c.face), c.uv.Vertices()[k].X, c.uv.Vertices()[k].Y).Normalize()}
+}
+
+// Edge returns the inward-facing normal of the great circle passing through
+// the CCW ordered edge from vertex k to vertex k+1 (mod 4) (for k = 0,1,2,3).
+func (c Cell) Edge(k int) Point {
+	switch k {
+	case 0:
+		return Point{vNorm(int(c.face), c.uv.Y.Lo).Normalize()} // Bottom
+	case 1:
+		return Point{uNorm(int(c.face), c.uv.X.Hi).Normalize()} // Right
+	case 2:
+		return Point{vNorm(int(c.face), c.uv.Y.Hi).Mul(-1.0).Normalize()} // Top
+	default:
+		return Point{uNorm(int(c.face), c.uv.X.Lo).Mul(-1.0).Normalize()} // Left
+	}
+}
+
+// BoundUV returns the bounds of this cell in (u,v)-space.
+func (c Cell) BoundUV() r2.Rect {
+	return c.uv
+}
+
+// Center returns the direction vector corresponding to the center in
+// (s,t)-space of the given cell. This is the point at which the cell is
+// divided into four subcells; it is not necessarily the centroid of the
+// cell in (u,v)-space or (x,y,z)-space
+func (c Cell) Center() Point {
+	return Point{c.id.rawPoint().Normalize()}
+}
+
+// Children returns the four direct children of this cell in traversal order
+// and returns true. If this is a leaf cell, or the children could not be created,
+// false is returned.
+// The C++ method is called Subdivide.
+func (c Cell) Children() ([4]Cell, bool) {
+	var children [4]Cell
+
+	if c.id.IsLeaf() {
+		return children, false
+	}
+
+	// Compute the cell midpoint in uv-space.
+	uvMid := c.id.centerUV()
+
+	// Create four children with the appropriate bounds.
+	cid := c.id.ChildBegin()
+	for pos := 0; pos < 4; pos++ {
+		children[pos] = Cell{
+			face:        c.face,
+			level:       c.level + 1,
+			orientation: c.orientation ^ int8(posToOrientation[pos]),
+			id:          cid,
+		}
+
+		// We want to split the cell in half in u and v. To decide which
+		// side to set equal to the midpoint value, we look at cell's (i,j)
+		// position within its parent. The index for i is in bit 1 of ij.
+		ij := posToIJ[c.orientation][pos]
+		i := ij >> 1
+		j := ij & 1
+		if i == 1 {
+			children[pos].uv.X.Hi = c.uv.X.Hi
+			children[pos].uv.X.Lo = uvMid.X
+		} else {
+			children[pos].uv.X.Lo = c.uv.X.Lo
+			children[pos].uv.X.Hi = uvMid.X
+		}
+		if j == 1 {
+			children[pos].uv.Y.Hi = c.uv.Y.Hi
+			children[pos].uv.Y.Lo = uvMid.Y
+		} else {
+			children[pos].uv.Y.Lo = c.uv.Y.Lo
+			children[pos].uv.Y.Hi = uvMid.Y
+		}
+		cid = cid.Next()
+	}
+	return children, true
+}
+
+// ExactArea returns the area of this cell as accurately as possible.
+func (c Cell) ExactArea() float64 {
+	v0, v1, v2, v3 := c.Vertex(0), c.Vertex(1), c.Vertex(2), c.Vertex(3)
+	return PointArea(v0, v1, v2) + PointArea(v0, v2, v3)
+}
+
+// ApproxArea returns the approximate area of this cell. This method is accurate
+// to within 3% percent for all cell sizes and accurate to within 0.1% for cells
+// at level 5 or higher (i.e. squares 350km to a side or smaller on the Earth's
+// surface). It is moderately cheap to compute.
+func (c Cell) ApproxArea() float64 {
+	// All cells at the first two levels have the same area.
+	if c.level < 2 {
+		return c.AverageArea()
+	}
+
+	// First, compute the approximate area of the cell when projected
+	// perpendicular to its normal. The cross product of its diagonals gives
+	// the normal, and the length of the normal is twice the projected area.
+	flatArea := 0.5 * (c.Vertex(2).Sub(c.Vertex(0).Vector).
+		Cross(c.Vertex(3).Sub(c.Vertex(1).Vector)).Norm())
+
+	// Now, compensate for the curvature of the cell surface by pretending
+	// that the cell is shaped like a spherical cap. The ratio of the
+	// area of a spherical cap to the area of its projected disc turns out
+	// to be 2 / (1 + sqrt(1 - r*r)) where r is the radius of the disc.
+	// For example, when r=0 the ratio is 1, and when r=1 the ratio is 2.
+	// Here we set Pi*r*r == flatArea to find the equivalent disc.
+	return flatArea * 2 / (1 + math.Sqrt(1-math.Min(1/math.Pi*flatArea, 1)))
+}
+
+// AverageArea returns the average area of cells at the level of this cell.
+// This is accurate to within a factor of 1.7.
+func (c Cell) AverageArea() float64 {
+	return AvgAreaMetric.Value(int(c.level))
+}
+
+// IntersectsCell reports whether the intersection of this cell and the other cell is not nil.
+func (c Cell) IntersectsCell(oc Cell) bool {
+	return c.id.Intersects(oc.id)
+}
+
+// ContainsCell reports whether this cell contains the other cell.
+func (c Cell) ContainsCell(oc Cell) bool {
+	return c.id.Contains(oc.id)
+}
+
+// CellUnionBound computes a covering of the Cell.
+func (c Cell) CellUnionBound() []CellID {
+	return c.CapBound().CellUnionBound()
+}
+
+// latitude returns the latitude of the cell vertex in radians given by (i,j),
+// where i and j indicate the Hi (1) or Lo (0) corner.
+func (c Cell) latitude(i, j int) float64 {
+	var u, v float64
+	switch {
+	case i == 0 && j == 0:
+		u = c.uv.X.Lo
+		v = c.uv.Y.Lo
+	case i == 0 && j == 1:
+		u = c.uv.X.Lo
+		v = c.uv.Y.Hi
+	case i == 1 && j == 0:
+		u = c.uv.X.Hi
+		v = c.uv.Y.Lo
+	case i == 1 && j == 1:
+		u = c.uv.X.Hi
+		v = c.uv.Y.Hi
+	default:
+		panic("i and/or j is out of bounds")
+	}
+	return latitude(Point{faceUVToXYZ(int(c.face), u, v)}).Radians()
+}
+
+// longitude returns the longitude of the cell vertex in radians given by (i,j),
+// where i and j indicate the Hi (1) or Lo (0) corner.
+func (c Cell) longitude(i, j int) float64 {
+	var u, v float64
+	switch {
+	case i == 0 && j == 0:
+		u = c.uv.X.Lo
+		v = c.uv.Y.Lo
+	case i == 0 && j == 1:
+		u = c.uv.X.Lo
+		v = c.uv.Y.Hi
+	case i == 1 && j == 0:
+		u = c.uv.X.Hi
+		v = c.uv.Y.Lo
+	case i == 1 && j == 1:
+		u = c.uv.X.Hi
+		v = c.uv.Y.Hi
+	default:
+		panic("i and/or j is out of bounds")
+	}
+	return longitude(Point{faceUVToXYZ(int(c.face), u, v)}).Radians()
+}
+
+var (
+	poleMinLat = math.Asin(math.Sqrt(1.0/3)) - 0.5*dblEpsilon
+)
+
+// RectBound returns the bounding rectangle of this cell.
+func (c Cell) RectBound() Rect {
+	if c.level > 0 {
+		// Except for cells at level 0, the latitude and longitude extremes are
+		// attained at the vertices.  Furthermore, the latitude range is
+		// determined by one pair of diagonally opposite vertices and the
+		// longitude range is determined by the other pair.
+		//
+		// We first determine which corner (i,j) of the cell has the largest
+		// absolute latitude.  To maximize latitude, we want to find the point in
+		// the cell that has the largest absolute z-coordinate and the smallest
+		// absolute x- and y-coordinates.  To do this we look at each coordinate
+		// (u and v), and determine whether we want to minimize or maximize that
+		// coordinate based on the axis direction and the cell's (u,v) quadrant.
+		u := c.uv.X.Lo + c.uv.X.Hi
+		v := c.uv.Y.Lo + c.uv.Y.Hi
+		var i, j int
+		if uAxis(int(c.face)).Z == 0 {
+			if u < 0 {
+				i = 1
+			}
+		} else if u > 0 {
+			i = 1
+		}
+		if vAxis(int(c.face)).Z == 0 {
+			if v < 0 {
+				j = 1
+			}
+		} else if v > 0 {
+			j = 1
+		}
+		lat := r1.IntervalFromPoint(c.latitude(i, j)).AddPoint(c.latitude(1-i, 1-j))
+		lng := s1.EmptyInterval().AddPoint(c.longitude(i, 1-j)).AddPoint(c.longitude(1-i, j))
+
+		// We grow the bounds slightly to make sure that the bounding rectangle
+		// contains LatLngFromPoint(P) for any point P inside the loop L defined by the
+		// four *normalized* vertices.  Note that normalization of a vector can
+		// change its direction by up to 0.5 * dblEpsilon radians, and it is not
+		// enough just to add Normalize calls to the code above because the
+		// latitude/longitude ranges are not necessarily determined by diagonally
+		// opposite vertex pairs after normalization.
+		//
+		// We would like to bound the amount by which the latitude/longitude of a
+		// contained point P can exceed the bounds computed above.  In the case of
+		// longitude, the normalization error can change the direction of rounding
+		// leading to a maximum difference in longitude of 2 * dblEpsilon.  In
+		// the case of latitude, the normalization error can shift the latitude by
+		// up to 0.5 * dblEpsilon and the other sources of error can cause the
+		// two latitudes to differ by up to another 1.5 * dblEpsilon, which also
+		// leads to a maximum difference of 2 * dblEpsilon.
+		return Rect{lat, lng}.expanded(LatLng{s1.Angle(2 * dblEpsilon), s1.Angle(2 * dblEpsilon)}).PolarClosure()
+	}
+
+	// The 4 cells around the equator extend to +/-45 degrees latitude at the
+	// midpoints of their top and bottom edges.  The two cells covering the
+	// poles extend down to +/-35.26 degrees at their vertices.  The maximum
+	// error in this calculation is 0.5 * dblEpsilon.
+	var bound Rect
+	switch c.face {
+	case 0:
+		bound = Rect{r1.Interval{-math.Pi / 4, math.Pi / 4}, s1.Interval{-math.Pi / 4, math.Pi / 4}}
+	case 1:
+		bound = Rect{r1.Interval{-math.Pi / 4, math.Pi / 4}, s1.Interval{math.Pi / 4, 3 * math.Pi / 4}}
+	case 2:
+		bound = Rect{r1.Interval{poleMinLat, math.Pi / 2}, s1.FullInterval()}
+	case 3:
+		bound = Rect{r1.Interval{-math.Pi / 4, math.Pi / 4}, s1.Interval{3 * math.Pi / 4, -3 * math.Pi / 4}}
+	case 4:
+		bound = Rect{r1.Interval{-math.Pi / 4, math.Pi / 4}, s1.Interval{-3 * math.Pi / 4, -math.Pi / 4}}
+	default:
+		bound = Rect{r1.Interval{-math.Pi / 2, -poleMinLat}, s1.FullInterval()}
+	}
+
+	// Finally, we expand the bound to account for the error when a point P is
+	// converted to an LatLng to test for containment. (The bound should be
+	// large enough so that it contains the computed LatLng of any contained
+	// point, not just the infinite-precision version.) We don't need to expand
+	// longitude because longitude is calculated via a single call to math.Atan2,
+	// which is guaranteed to be semi-monotonic.
+	return bound.expanded(LatLng{s1.Angle(dblEpsilon), s1.Angle(0)})
+}
+
+// CapBound returns the bounding cap of this cell.
+func (c Cell) CapBound() Cap {
+	// We use the cell center in (u,v)-space as the cap axis.  This vector is very close
+	// to GetCenter() and faster to compute.  Neither one of these vectors yields the
+	// bounding cap with minimal surface area, but they are both pretty close.
+	cap := CapFromPoint(Point{faceUVToXYZ(int(c.face), c.uv.Center().X, c.uv.Center().Y).Normalize()})
+	for k := 0; k < 4; k++ {
+		cap = cap.AddPoint(c.Vertex(k))
+	}
+	return cap
+}
+
+// ContainsPoint reports whether this cell contains the given point. Note that
+// unlike Loop/Polygon, a Cell is considered to be a closed set. This means
+// that a point on a Cell's edge or vertex belong to the Cell and the relevant
+// adjacent Cells too.
+//
+// If you want every point to be contained by exactly one Cell,
+// you will need to convert the Cell to a Loop.
+func (c Cell) ContainsPoint(p Point) bool {
+	var uv r2.Point
+	var ok bool
+	if uv.X, uv.Y, ok = faceXYZToUV(int(c.face), p); !ok {
+		return false
+	}
+
+	// Expand the (u,v) bound to ensure that
+	//
+	//   CellFromPoint(p).ContainsPoint(p)
+	//
+	// is always true. To do this, we need to account for the error when
+	// converting from (u,v) coordinates to (s,t) coordinates. In the
+	// normal case the total error is at most dblEpsilon.
+	return c.uv.ExpandedByMargin(dblEpsilon).ContainsPoint(uv)
+}
+
+// Encode encodes the Cell.
+func (c Cell) Encode(w io.Writer) error {
+	e := &encoder{w: w}
+	c.encode(e)
+	return e.err
+}
+
+func (c Cell) encode(e *encoder) {
+	c.id.encode(e)
+}
+
+// Decode decodes the Cell.
+func (c *Cell) Decode(r io.Reader) error {
+	d := &decoder{r: asByteReader(r)}
+	c.decode(d)
+	return d.err
+}
+
+func (c *Cell) decode(d *decoder) {
+	c.id.decode(d)
+	*c = CellFromCellID(c.id)
+}
+
+// vertexChordDist2 returns the squared chord distance from point P to the
+// given corner vertex specified by the Hi or Lo values of each.
+func (c Cell) vertexChordDist2(p Point, xHi, yHi bool) s1.ChordAngle {
+	x := c.uv.X.Lo
+	y := c.uv.Y.Lo
+	if xHi {
+		x = c.uv.X.Hi
+	}
+	if yHi {
+		y = c.uv.Y.Hi
+	}
+
+	return ChordAngleBetweenPoints(p, PointFromCoords(x, y, 1))
+}
+
+// uEdgeIsClosest reports whether a point P is closer to the interior of the specified
+// Cell edge (either the lower or upper edge of the Cell) or to the endpoints.
+func (c Cell) uEdgeIsClosest(p Point, vHi bool) bool {
+	u0 := c.uv.X.Lo
+	u1 := c.uv.X.Hi
+	v := c.uv.Y.Lo
+	if vHi {
+		v = c.uv.Y.Hi
+	}
+	// These are the normals to the planes that are perpendicular to the edge
+	// and pass through one of its two endpoints.
+	dir0 := r3.Vector{v*v + 1, -u0 * v, -u0}
+	dir1 := r3.Vector{v*v + 1, -u1 * v, -u1}
+	return p.Dot(dir0) > 0 && p.Dot(dir1) < 0
+}
+
+// vEdgeIsClosest reports whether a point P is closer to the interior of the specified
+// Cell edge (either the right or left edge of the Cell) or to the endpoints.
+func (c Cell) vEdgeIsClosest(p Point, uHi bool) bool {
+	v0 := c.uv.Y.Lo
+	v1 := c.uv.Y.Hi
+	u := c.uv.X.Lo
+	if uHi {
+		u = c.uv.X.Hi
+	}
+	dir0 := r3.Vector{-u * v0, u*u + 1, -v0}
+	dir1 := r3.Vector{-u * v1, u*u + 1, -v1}
+	return p.Dot(dir0) > 0 && p.Dot(dir1) < 0
+}
+
+// edgeDistance reports the distance from a Point P to a given Cell edge. The point
+// P is given by its dot product, and the uv edge by its normal in the
+// given coordinate value.
+func edgeDistance(ij, uv float64) s1.ChordAngle {
+	// Let P by the target point and let R be the closest point on the given
+	// edge AB.  The desired distance PR can be expressed as PR^2 = PQ^2 + QR^2
+	// where Q is the point P projected onto the plane through the great circle
+	// through AB.  We can compute the distance PQ^2 perpendicular to the plane
+	// from "dirIJ" (the dot product of the target point P with the edge
+	// normal) and the squared length the edge normal (1 + uv**2).
+	pq2 := (ij * ij) / (1 + uv*uv)
+
+	// We can compute the distance QR as (1 - OQ) where O is the sphere origin,
+	// and we can compute OQ^2 = 1 - PQ^2 using the Pythagorean theorem.
+	// (This calculation loses accuracy as angle POQ approaches Pi/2.)
+	qr := 1 - math.Sqrt(1-pq2)
+	return s1.ChordAngleFromSquaredLength(pq2 + qr*qr)
+}
+
+// distanceInternal reports the distance from the given point to the interior of
+// the cell if toInterior is true or to the boundary of the cell otherwise.
+func (c Cell) distanceInternal(targetXYZ Point, toInterior bool) s1.ChordAngle {
+	// All calculations are done in the (u,v,w) coordinates of this cell's face.
+	target := faceXYZtoUVW(int(c.face), targetXYZ)
+
+	// Compute dot products with all four upward or rightward-facing edge
+	// normals. dirIJ is the dot product for the edge corresponding to axis
+	// I, endpoint J. For example, dir01 is the right edge of the Cell
+	// (corresponding to the upper endpoint of the u-axis).
+	dir00 := target.X - target.Z*c.uv.X.Lo
+	dir01 := target.X - target.Z*c.uv.X.Hi
+	dir10 := target.Y - target.Z*c.uv.Y.Lo
+	dir11 := target.Y - target.Z*c.uv.Y.Hi
+	inside := true
+	if dir00 < 0 {
+		inside = false // Target is to the left of the cell
+		if c.vEdgeIsClosest(target, false) {
+			return edgeDistance(-dir00, c.uv.X.Lo)
+		}
+	}
+	if dir01 > 0 {
+		inside = false // Target is to the right of the cell
+		if c.vEdgeIsClosest(target, true) {
+			return edgeDistance(dir01, c.uv.X.Hi)
+		}
+	}
+	if dir10 < 0 {
+		inside = false // Target is below the cell
+		if c.uEdgeIsClosest(target, false) {
+			return edgeDistance(-dir10, c.uv.Y.Lo)
+		}
+	}
+	if dir11 > 0 {
+		inside = false // Target is above the cell
+		if c.uEdgeIsClosest(target, true) {
+			return edgeDistance(dir11, c.uv.Y.Hi)
+		}
+	}
+	if inside {
+		if toInterior {
+			return s1.ChordAngle(0)
+		}
+		// Although you might think of Cells as rectangles, they are actually
+		// arbitrary quadrilaterals after they are projected onto the sphere.
+		// Therefore the simplest approach is just to find the minimum distance to
+		// any of the four edges.
+		return minChordAngle(edgeDistance(-dir00, c.uv.X.Lo),
+			edgeDistance(dir01, c.uv.X.Hi),
+			edgeDistance(-dir10, c.uv.Y.Lo),
+			edgeDistance(dir11, c.uv.Y.Hi))
+	}
+
+	// Otherwise, the closest point is one of the four cell vertices. Note that
+	// it is *not* trivial to narrow down the candidates based on the edge sign
+	// tests above, because (1) the edges don't meet at right angles and (2)
+	// there are points on the far side of the sphere that are both above *and*
+	// below the cell, etc.
+	return minChordAngle(c.vertexChordDist2(target, false, false),
+		c.vertexChordDist2(target, true, false),
+		c.vertexChordDist2(target, false, true),
+		c.vertexChordDist2(target, true, true))
+}
+
+// Distance reports the distance from the cell to the given point. Returns zero if
+// the point is inside the cell.
+func (c Cell) Distance(target Point) s1.ChordAngle {
+	return c.distanceInternal(target, true)
+}
+
+// MaxDistance reports the maximum distance from the cell (including its interior) to the
+// given point.
+func (c Cell) MaxDistance(target Point) s1.ChordAngle {
+	// First check the 4 cell vertices.  If all are within the hemisphere
+	// centered around target, the max distance will be to one of these vertices.
+	targetUVW := faceXYZtoUVW(int(c.face), target)
+	maxDist := maxChordAngle(c.vertexChordDist2(targetUVW, false, false),
+		c.vertexChordDist2(targetUVW, true, false),
+		c.vertexChordDist2(targetUVW, false, true),
+		c.vertexChordDist2(targetUVW, true, true))
+
+	if maxDist <= s1.RightChordAngle {
+		return maxDist
+	}
+
+	// Otherwise, find the minimum distance dMin to the antipodal point and the
+	// maximum distance will be pi - dMin.
+	return s1.StraightChordAngle - c.BoundaryDistance(Point{target.Mul(-1)})
+}
+
+// BoundaryDistance reports the distance from the cell boundary to the given point.
+func (c Cell) BoundaryDistance(target Point) s1.ChordAngle {
+	return c.distanceInternal(target, false)
+}
+
+// DistanceToEdge returns the minimum distance from the cell to the given edge AB. Returns
+// zero if the edge intersects the cell interior.
+func (c Cell) DistanceToEdge(a, b Point) s1.ChordAngle {
+	// Possible optimizations:
+	//  - Currently the (cell vertex, edge endpoint) distances are computed
+	//    twice each, and the length of AB is computed 4 times.
+	//  - To fix this, refactor GetDistance(target) so that it skips calculating
+	//    the distance to each cell vertex. Instead, compute the cell vertices
+	//    and distances in this function, and add a low-level UpdateMinDistance
+	//    that allows the XA, XB, and AB distances to be passed in.
+	//  - It might also be more efficient to do all calculations in UVW-space,
+	//    since this would involve transforming 2 points rather than 4.
+
+	// First, check the minimum distance to the edge endpoints A and B.
+	// (This also detects whether either endpoint is inside the cell.)
+	minDist := minChordAngle(c.Distance(a), c.Distance(b))
+	if minDist == 0 {
+		return minDist
+	}
+
+	// Otherwise, check whether the edge crosses the cell boundary.
+	crosser := NewChainEdgeCrosser(a, b, c.Vertex(3))
+	for i := 0; i < 4; i++ {
+		if crosser.ChainCrossingSign(c.Vertex(i)) != DoNotCross {
+			return 0
+		}
+	}
+
+	// Finally, check whether the minimum distance occurs between a cell vertex
+	// and the interior of the edge AB. (Some of this work is redundant, since
+	// it also checks the distance to the endpoints A and B again.)
+	//
+	// Note that we don't need to check the distance from the interior of AB to
+	// the interior of a cell edge, because the only way that this distance can
+	// be minimal is if the two edges cross (already checked above).
+	for i := 0; i < 4; i++ {
+		minDist, _ = UpdateMinDistance(c.Vertex(i), a, b, minDist)
+	}
+	return minDist
+}
+
+// MaxDistanceToEdge returns the maximum distance from the cell (including its interior)
+// to the given edge AB.
+func (c Cell) MaxDistanceToEdge(a, b Point) s1.ChordAngle {
+	// If the maximum distance from both endpoints to the cell is less than π/2
+	// then the maximum distance from the edge to the cell is the maximum of the
+	// two endpoint distances.
+	maxDist := maxChordAngle(c.MaxDistance(a), c.MaxDistance(b))
+	if maxDist <= s1.RightChordAngle {
+		return maxDist
+	}
+
+	return s1.StraightChordAngle - c.DistanceToEdge(Point{a.Mul(-1)}, Point{b.Mul(-1)})
+}
+
+// DistanceToCell returns the minimum distance from this cell to the given cell.
+// It returns zero if one cell contains the other.
+func (c Cell) DistanceToCell(target Cell) s1.ChordAngle {
+	// If the cells intersect, the distance is zero.  We use the (u,v) ranges
+	// rather than CellID intersects so that cells that share a partial edge or
+	// corner are considered to intersect.
+	if c.face == target.face && c.uv.Intersects(target.uv) {
+		return 0
+	}
+
+	// Otherwise, the minimum distance always occurs between a vertex of one
+	// cell and an edge of the other cell (including the edge endpoints).  This
+	// represents a total of 32 possible (vertex, edge) pairs.
+	//
+	// TODO(roberts): This could be optimized to be at least 5x faster by pruning
+	// the set of possible closest vertex/edge pairs using the faces and (u,v)
+	// ranges of both cells.
+	var va, vb [4]Point
+	for i := 0; i < 4; i++ {
+		va[i] = c.Vertex(i)
+		vb[i] = target.Vertex(i)
+	}
+	minDist := s1.InfChordAngle()
+	for i := 0; i < 4; i++ {
+		for j := 0; j < 4; j++ {
+			minDist, _ = UpdateMinDistance(va[i], vb[j], vb[(j+1)&3], minDist)
+			minDist, _ = UpdateMinDistance(vb[i], va[j], va[(j+1)&3], minDist)
+		}
+	}
+	return minDist
+}
+
+// MaxDistanceToCell returns the maximum distance from the cell (including its
+// interior) to the given target cell.
+func (c Cell) MaxDistanceToCell(target Cell) s1.ChordAngle {
+	// Need to check the antipodal target for intersection with the cell. If it
+	// intersects, the distance is the straight ChordAngle.
+	// antipodalUV is the transpose of the original UV, interpreted within the opposite face.
+	antipodalUV := r2.Rect{target.uv.Y, target.uv.X}
+	if int(c.face) == oppositeFace(int(target.face)) && c.uv.Intersects(antipodalUV) {
+		return s1.StraightChordAngle
+	}
+
+	// Otherwise, the maximum distance always occurs between a vertex of one
+	// cell and an edge of the other cell (including the edge endpoints).  This
+	// represents a total of 32 possible (vertex, edge) pairs.
+	//
+	// TODO(roberts): When the maximum distance is at most π/2, the maximum is
+	// always attained between a pair of vertices, and this could be made much
+	// faster by testing each vertex pair once rather than the current 4 times.
+	var va, vb [4]Point
+	for i := 0; i < 4; i++ {
+		va[i] = c.Vertex(i)
+		vb[i] = target.Vertex(i)
+	}
+	maxDist := s1.NegativeChordAngle
+	for i := 0; i < 4; i++ {
+		for j := 0; j < 4; j++ {
+			maxDist, _ = UpdateMaxDistance(va[i], vb[j], vb[(j+1)&3], maxDist)
+			maxDist, _ = UpdateMaxDistance(vb[i], va[j], va[(j+1)&3], maxDist)
+		}
+	}
+	return maxDist
+}