void TestProjectUnproject(Projection projection, R2Point px, S2Point x)
{
// The arguments are chosen such that projection is exact, but
// unprojection may not be.
Assert.Equal(px, projection.Project(x));
Assert.True(S2.ApproxEquals(x, projection.Unproject(px)));
}
public void Test_R2Rect_SimplePredicates()
{
// GetCenter(), GetVertex(), Contains(R2Point), InteriorContains(R2Point).
R2Point sw1 = new(0, 0.25);
R2Point ne1 = new(0.5, 0.75);
R2Rect r1 = new(sw1, ne1);
Assert.Equal(new R2Point(0.25, 0.5), r1.GetCenter());
Assert.Equal(new R2Point(0, 0.25), r1.GetVertex(0));
Assert.Equal(new R2Point(0.5, 0.25), r1.GetVertex(1));
Assert.Equal(new R2Point(0.5, 0.75), r1.GetVertex(2));
Assert.Equal(new R2Point(0, 0.75), r1.GetVertex(3));
Assert.True(r1.Contains(new R2Point(0.2, 0.4)));
Assert.False(r1.Contains(new R2Point(0.2, 0.8)));
Assert.False(r1.Contains(new R2Point(-0.1, 0.4)));
Assert.False(r1.Contains(new R2Point(0.6, 0.1)));
Assert.True(r1.Contains(sw1));
Assert.True(r1.Contains(ne1));
Assert.False(r1.InteriorContains(sw1));
Assert.False(r1.InteriorContains(ne1));
// Make sure that GetVertex() returns vertices in CCW order.
for (int k = 0; k < 4; ++k)
{
R2Point a = r1.GetVertex(k - 1);
R2Point b = r1.GetVertex(k);
R2Point c = r1.GetVertex(k + 1);
Assert.True((b - a).GetOrtho().DotProd(c - a) > 0);
}
}
private static void TestIntervalOps(S1Interval x, S1Interval y, string expected_relation, S1Interval expected_union, S1Interval expected_intersection)
{
// Test all of the interval operations on the given pair of intervals.
// "expected_relation" is a sequence of "T" and "F" characters corresponding
// to the expected results of Contains(), InteriorContains(), Intersects(),
// and InteriorIntersects() respectively.
Assert.Equal(x.Contains(y), expected_relation[0] == 'T');
Assert.Equal(x.InteriorContains(y), expected_relation[1] == 'T');
Assert.Equal(x.Intersects(y), expected_relation[2] == 'T');
Assert.Equal(x.InteriorIntersects(y), expected_relation[3] == 'T');
// bounds() returns a reference to a member variable, so we need to
// make a copy when invoking it on a temporary object.
Assert.Equal(R2Point.FromCoords(x.Union(y).Bounds()).Bounds(), expected_union.Bounds());
Assert.Equal(R2Point.FromCoords(x.Intersection(y).Bounds()).Bounds(),
expected_intersection.Bounds());
Assert.Equal(x.Contains(y), x.Union(y) == x);
Assert.Equal(x.Intersects(y), !x.Intersection(y).IsEmpty());
if (y.Lo == y.Hi)
{
var r = S1Interval.AddPoint(x, y.Lo);
Assert.Equal(r.Bounds(), expected_union.Bounds());
}
}
// Given a point P representing a possibly clipped endpoint A of an edge AB,
// verify that "clip" contains P, and that if clipping occurred (i.e., P != A)
// then P is on the boundary of "clip".
private static void CheckPointOnBoundary(R2Point p, R2Point a, R2Rect clip)
{
Assert.True(clip.Contains(p));
if (p != a)
{
Assert.False(clip.Contains(new R2Point(MathUtils.NextAfter(p[0], a[0]),
MathUtils.NextAfter(p[1], a[1]))));
}
}
public override S2LatLng ToLatLng(R2Point p)
{
// This formula is more accurate near zero than the atan(exp()) version.
double x = to_radians_ * Math.IEEERemainder(p.X, x_wrap_);
double k = Math.Exp(2 * to_radians_ * p.Y);
double y = double.IsInfinity(k) ? S2.M_PI_2 : Math.Asin((k - 1) / (k + 1));
return(S2LatLng.FromRadians(y, x));
}
// Given an edge AB and a rectangle "clip", verify that IntersectsRect(),
// ClipEdge(), and ClipEdgeBound() produce consistent results.
private static void TestClipEdge(R2Point a, R2Point b, R2Rect clip)
{
// A bound for the error in edge clipping plus the error in the
// IntersectsRect calculation below.
double kError = kEdgeClipErrorUVDist + kIntersectsRectErrorUVDist;
if (!ClipEdge(a, b, clip, out var a_clipped, out var b_clipped))
{
Assert.False(IntersectsRect(a, b, clip.Expanded(-kError)));
}
// Given a point X on the line AB (which is checked), return the fraction "t"
// such that x = (1-t)*a + t*b. Return 0 if A = B.
private static double GetFraction(R2Point x, R2Point a, R2Point b)
{
// A bound for the error in edge clipping plus the error in the calculation
// below (which is similar to IntersectsRect).
double kError = kEdgeClipErrorUVDist + kIntersectsRectErrorUVDist;
if (a == b)
{
return(0.0);
}
R2Point dir = R2Point.Normalize(b - a);
Assert.True(Math.Abs((x - a).DotProd(dir.GetOrtho())) <= kError);
return((x - a).DotProd(dir));
}
// Given a geodesic edge AB, split the edge as necessary and append all
// projected vertices except the first to "vertices".
//
// The maximum recursion depth is (Math.PI / kMinTolerance()) < 45, and the
// frame size is small so stack overflow should not be an issue.
private void AppendProjected(R2Point pa, S2Point a, R2Point pb, S2Point b, List <R2Point> vertices)
{
R2Point pbTmp = proj_.WrapDestination(pa, pb);
if (EstimateMaxError(pa, a, pbTmp, b) <= scaled_tolerance_)
{
vertices.Add(pbTmp);
}
else
{
var mid = (a + b).Normalize();
var pmid = proj_.WrapDestination(pa, proj_.Project(mid));
AppendProjected(pa, a, pmid, mid, vertices);
AppendProjected(pmid, mid, pbTmp, b, vertices);
}
}
// Helper function that wraps the coordinates of B if necessary in order to
// obtain the shortest edge AB. For example, suppose that A = [170, 20],
// B = [-170, 20], and the projection wraps so that [x, y] == [x + 360, y].
// Then this function would return [190, 20] for point B (reducing the edge
// length in the "x" direction from 340 to 20).
public R2Point WrapDestination(R2Point a, R2Point b)
{
R2Point wrap = WrapDistance();
double x = b.X, y = b.Y;
// The code below ensures that "b" is unmodified unless wrapping is required.
if (wrap.X > 0 && Math.Abs(x - a.X) > 0.5 * wrap.X)
{
x = a.X + Math.IEEERemainder(x - a.X, wrap.X);
}
if (wrap.Y > 0 && Math.Abs(y - a.Y) > 0.5 * wrap.Y)
{
y = a.Y + Math.IEEERemainder(y - a.Y, wrap.Y);
}
return(new R2Point(x, y));
}
// Like AppendProjected, but interpolates a projected edge and appends the
// corresponding points on the sphere.
private void AppendUnprojected(R2Point pa, S2Point a, R2Point pb, S2Point b, List <S2Point> vertices)
{
// See notes above regarding measuring the interpolation error.
var pbTmp = proj_.WrapDestination(pa, pb);
if (EstimateMaxError(pa, a, pbTmp, b) <= scaled_tolerance_)
{
vertices.Add(b);
}
else
{
R2Point pmid = Projection.Interpolate(0.5, pa, pbTmp);
S2Point mid = proj_.Unproject(pmid);
AppendUnprojected(pa, a, pmid, mid, vertices);
AppendUnprojected(pmid, mid, pbTmp, b, vertices);
}
}
// Choose a random point in the rectangle defined by points A and B, sometimes
// returning a point on the edge AB or the points A and B themselves.
private static R2Point ChooseRectPoint(R2Point a, R2Point b)
{
if (S2Testing.Random.OneIn(5))
{
return(S2Testing.Random.OneIn(2) ? a : b);
}
else if (S2Testing.Random.OneIn(3))
{
return(a + S2Testing.Random.RandDouble() * (b - a));
}
else
{
// a[i] may be >, <, or == b[i], so we write it like this instead
// of using UniformDouble.
return(new R2Point(a[0] + S2Testing.Random.RandDouble() * (b[0] - a[0]),
a[1] + S2Testing.Random.RandDouble() * (b[1] - a[1])));
}
}
public void Test_PlateCarreeProjection_Interpolate()
{
PlateCarreeProjection proj = new(180);
// Test that coordinates and/or arguments are not accidentally reversed.
Assert.Equal(new R2Point(1.5, 6),
Projection.Interpolate(0.25, new R2Point(1, 5), new R2Point(3, 9)));
// Test extrapolation.
Assert.Equal(new R2Point(-3, 0), Projection.Interpolate(-2, new R2Point(1, 0), new R2Point(3, 0)));
// Check that interpolation is exact at both endpoints.
var a = new R2Point(1.234, -5.456e-20);
var b = new R2Point(2.1234e-20, 7.456);
Assert.Equal(a, Projection.Interpolate(0, a, b));
Assert.Equal(b, Projection.Interpolate(1, a, b));
}
public void Test_S2PaddedCell_ShrinkToFit()
{
const int kIters = 1000;
for (int iter = 0; iter < kIters; ++iter)
{
// Start with the desired result and work backwards.
S2CellId result = S2Testing.GetRandomCellId();
R2Rect result_uv = result.BoundUV();
R2Point size_uv = result_uv.GetSize();
// Find the biggest rectangle that fits in "result" after padding.
// (These calculations ignore numerical errors.)
double max_padding = 0.5 * Math.Min(size_uv[0], size_uv[1]);
double padding = max_padding * S2Testing.Random.RandDouble();
R2Rect max_rect = result_uv.Expanded(-padding);
// Start with a random subset of the maximum rectangle.
R2Point a = new(SampleInterval(max_rect[0]), SampleInterval(max_rect[1]));
R2Point b = new(SampleInterval(max_rect[0]), SampleInterval(max_rect[1]));
if (!result.IsLeaf())
{
// If the result is not a leaf cell, we must ensure that no child of
// "result" also satisfies the conditions of ShrinkToFit(). We do this
// by ensuring that "rect" intersects at least two children of "result"
// (after padding).
int axis = S2Testing.Random.Uniform(2);
double center = result.CenterUV()[axis];
// Find the range of coordinates that are shared between child cells
// along that axis.
R1Interval shared = new(center - padding, center + padding);
double mid = SampleInterval(shared.Intersection(max_rect[axis]));
a = a.SetAxis(axis, SampleInterval(new R1Interval(max_rect[axis].Lo, mid)));
b = b.SetAxis(axis, SampleInterval(new R1Interval(mid, max_rect[axis].Hi)));
}
R2Rect rect = R2Rect.FromPointPair(a, b);
// Choose an arbitrary ancestor as the S2PaddedCell.
S2CellId initial_id = result.Parent(S2Testing.Random.Uniform(result.Level() + 1));
Assert.Equal(result, new S2PaddedCell(initial_id, padding).ShrinkToFit(rect));
}
}
private S1ChordAngle EstimateMaxError(R2Point pa, S2Point a, R2Point pb, S2Point b)
{
// See the algorithm description at the top of this file.
// We always tessellate edges longer than 90 degrees on the sphere, since the
// approximation below is not robust enough to handle such edges.
if (a.DotProd(b) < -1e-14)
{
return(S1ChordAngle.Infinity);
}
const double t1 = kInterpolationFraction;
const double t2 = 1 - kInterpolationFraction;
S2Point mid1 = S2.Interpolate(a, b, t1);
S2Point mid2 = S2.Interpolate(a, b, t2);
S2Point pmid1 = proj_.Unproject(Projection.Interpolate(t1, pa, pb));
S2Point pmid2 = proj_.Unproject(Projection.Interpolate(t2, pa, pb));
return(S1ChordAngle.Max(new S1ChordAngle(mid1, pmid1), new S1ChordAngle(mid2, pmid2)));
}
// Converts the planar edge AB in the given projection to a chain of
// spherical geodesic edges and appends the vertices to "vertices".
//
// This method can be called multiple times with the same output vector to
// convert an entire polyline or loop. All vertices of the first edge are
// appended, but the first vertex of each subsequent edge is omitted (and is
// required to match that last vertex of the previous edge).
//
// Note that to construct an S2Loop, you must call vertices.pop_back() at
// the very end to eliminate the duplicate first and last vertex. Note also
// that if the given projection involves coordinate "wrapping" (e.g. across
// the 180 degree meridian) then the first and last vertices may not be
// exactly the same.
public void AppendUnprojected(R2Point a, R2Point b, List <S2Point> vertices)
{
var pointA = proj_.Unproject(a);
var pointB = proj_.Unproject(b);
if (!vertices.Any())
{
vertices.Add(pointA);
}
else
{
// Note that coordinate wrapping can create a small amount of error. For
// example in the edge chain "0:-175, 0:179, 0:-177", the first edge is
// transformed into "0:-175, 0:-181" while the second is transformed into
// "0:179, 0:183". The two coordinate pairs for the middle vertex
// ("0:-181" and "0:179") may not yield exactly the same S2Point.
System.Diagnostics.Debug.Assert(S2.ApproxEquals(vertices.Last(), pointA)); // Appended edges must form a chain
}
AppendUnprojected(a, pointA, b, pointB, vertices);
}
// Returns the point obtained by interpolating the given fraction of the
// distance along the line from A to B. Almost all projections should
// use the default implementation of this method, which simply interpolates
// linearly in R2 space. Fractions < 0 or > 1 result in extrapolation
// instead.
//
// The only reason to override this method is if you want edges to be
// defined as something other than straight lines in the 2D projected
// coordinate system. For example, using a third-party library such as
// GeographicLib you could define edges as geodesics over an ellipsoid model
// of the Earth. (Note that very few data sets define edges this way.)
//
// Also note that there is no reason to define a projection where edges are
// geodesics over the sphere, because this is the native S2 interpretation.
public static R2Point Interpolate(double f, R2Point a, R2Point b)
{
// Default implementation, suitable for any projection where edges are defined
// as straight lines in the 2D projected space.
return((1.0 - f) * a + f * b);
}
// Convenience function equivalent to S2LatLng(Unproject(p)), but the // implementation may be more efficient. public abstract S2LatLng ToLatLng(R2Point p);
public override S2LatLng ToLatLng(R2Point p)
{
var rem = Math.IEEERemainder(p.X, x_wrap_);
return(S2LatLng.FromRadians(to_radians_ * p.Y, to_radians_ * rem));
}
// Converts a projected 2D point to a point on the sphere. // // If wrapping is defined for a given axis (see below), then this method // should accept any real number for the corresponding coordinate. public abstract S2Point Unproject(R2Point p);
public override S2Point Unproject(R2Point p)
{
return(ToLatLng(p).ToPoint());
}
