예제 #1
0
// InterpolateAtDistance returns the point X along the line segment AB whose
// distance from A is the angle ax.
func InterpolateAtDistance(ax s1.Angle, a, b Point) Point {
	aRad := ax.Radians()

	// Use PointCross to compute the tangent vector at A towards B. The
	// result is always perpendicular to A, even if A=B or A=-B, but it is not
	// necessarily unit length. (We effectively normalize it below.)
	normal := a.PointCross(b)
	tangent := normal.Vector.Cross(a.Vector)

	// Now compute the appropriate linear combination of A and "tangent". With
	// infinite precision the result would always be unit length, but we
	// normalize it anyway to ensure that the error is within acceptable bounds.
	// (Otherwise errors can build up when the result of one interpolation is
	// fed into another interpolation.)
	return Point{(a.Mul(math.Cos(aRad)).Add(tangent.Mul(math.Sin(aRad) / tangent.Norm()))).Normalize()}
}
예제 #2
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파일: cap.go 프로젝트: jinshuangxian/geo
// radiusToHeight converts an s1.Angle into the height of the cap.
func radiusToHeight(r s1.Angle) float64 {
	if r.Radians() < 0 {
		return emptyHeight
	}
	if r.Radians() >= math.Pi {
		return fullHeight
	}
	// The height of the cap can be computed as 1 - cos(r), but this isn't very
	// accurate for angles close to zero (where cos(r) is almost 1). The
	// formula below has much better precision.
	d := math.Sin(0.5 * r.Radians())
	return 2 * d * d

}
예제 #3
0
파일: earth.go 프로젝트: dgraph-io/dgraph
// EarthDistance converts an angle to distance on earth in meters.
func EarthDistance(angle s1.Angle) Length {
	return Length(angle.Radians() * EarthRadiusMeters)
}