Grand test fixup (#138)

* start fixing up tests

* fix up tests + automate with drone

* fiddle with linting

* messing about with drone.yml

* some more fiddling

* hmmm

* add cache

* add vendor directory

* verbose

* ci updates

* update some little things

* update sig

vendor/github.com/golang/geo/s1/chordangle.go

@@ -0,0 +1,320 @@
+// Copyright 2015 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 s1
+
+import (
+	"math"
+)
+
+// ChordAngle represents the angle subtended by a chord (i.e., the straight
+// line segment connecting two points on the sphere). Its representation
+// makes it very efficient for computing and comparing distances, but unlike
+// Angle it is only capable of representing angles between 0 and π radians.
+// Generally, ChordAngle should only be used in loops where many angles need
+// to be calculated and compared. Otherwise it is simpler to use Angle.
+//
+// ChordAngle loses some accuracy as the angle approaches π radians.
+// There are several different ways to measure this error, including the
+// representational error (i.e., how accurately ChordAngle can represent
+// angles near π radians), the conversion error (i.e., how much precision is
+// lost when an Angle is converted to an ChordAngle), and the measurement
+// error (i.e., how accurate the ChordAngle(a, b) constructor is when the
+// points A and B are separated by angles close to π radians). All of these
+// errors differ by a small constant factor.
+//
+// For the measurement error (which is the largest of these errors and also
+// the most important in practice), let the angle between A and B be (π - x)
+// radians, i.e. A and B are within "x" radians of being antipodal. The
+// corresponding chord length is
+//
+//    r = 2 * sin((π - x) / 2) = 2 * cos(x / 2)
+//
+// For values of x not close to π the relative error in the squared chord
+// length is at most 4.5 * dblEpsilon (see MaxPointError below).
+// The relative error in "r" is thus at most 2.25 * dblEpsilon ~= 5e-16. To
+// convert this error into an equivalent angle, we have
+//
+//    |dr / dx| = sin(x / 2)
+//
+// and therefore
+//
+//    |dx| = dr / sin(x / 2)
+//         = 5e-16 * (2 * cos(x / 2)) / sin(x / 2)
+//         = 1e-15 / tan(x / 2)
+//
+// The maximum error is attained when
+//
+//    x  = |dx|
+//       = 1e-15 / tan(x / 2)
+//      ~= 1e-15 / (x / 2)
+//      ~= sqrt(2e-15)
+//
+// In summary, the measurement error for an angle (π - x) is at most
+//
+//    dx  = min(1e-15 / tan(x / 2), sqrt(2e-15))
+//      (~= min(2e-15 / x, sqrt(2e-15)) when x is small)
+//
+// On the Earth's surface (assuming a radius of 6371km), this corresponds to
+// the following worst-case measurement errors:
+//
+//     Accuracy:             Unless antipodal to within:
+//     ---------             ---------------------------
+//     6.4 nanometers        10,000 km (90 degrees)
+//     1 micrometer          81.2 kilometers
+//     1 millimeter          81.2 meters
+//     1 centimeter          8.12 meters
+//     28.5 centimeters      28.5 centimeters
+//
+// The representational and conversion errors referred to earlier are somewhat
+// smaller than this. For example, maximum distance between adjacent
+// representable ChordAngle values is only 13.5 cm rather than 28.5 cm. To
+// see this, observe that the closest representable value to r^2 = 4 is
+// r^2 =  4 * (1 - dblEpsilon / 2). Thus r = 2 * (1 - dblEpsilon / 4) and
+// the angle between these two representable values is
+//
+//    x  = 2 * acos(r / 2)
+//       = 2 * acos(1 - dblEpsilon / 4)
+//      ~= 2 * asin(sqrt(dblEpsilon / 2)
+//      ~= sqrt(2 * dblEpsilon)
+//      ~= 2.1e-8
+//
+// which is 13.5 cm on the Earth's surface.
+//
+// The worst case rounding error occurs when the value halfway between these
+// two representable values is rounded up to 4. This halfway value is
+// r^2 = (4 * (1 - dblEpsilon / 4)), thus r = 2 * (1 - dblEpsilon / 8) and
+// the worst case rounding error is
+//
+//    x  = 2 * acos(r / 2)
+//       = 2 * acos(1 - dblEpsilon / 8)
+//      ~= 2 * asin(sqrt(dblEpsilon / 4)
+//      ~= sqrt(dblEpsilon)
+//      ~= 1.5e-8
+//
+// which is 9.5 cm on the Earth's surface.
+type ChordAngle float64
+
+const (
+	// NegativeChordAngle represents a chord angle smaller than the zero angle.
+	// The only valid operations on a NegativeChordAngle are comparisons,
+	// Angle conversions, and Successor/Predecessor.
+	NegativeChordAngle = ChordAngle(-1)
+
+	// RightChordAngle represents a chord angle of 90 degrees (a "right angle").
+	RightChordAngle = ChordAngle(2)
+
+	// StraightChordAngle represents a chord angle of 180 degrees (a "straight angle").
+	// This is the maximum finite chord angle.
+	StraightChordAngle = ChordAngle(4)
+
+	// maxLength2 is the square of the maximum length allowed in a ChordAngle.
+	maxLength2 = 4.0
+)
+
+// ChordAngleFromAngle returns a ChordAngle from the given Angle.
+func ChordAngleFromAngle(a Angle) ChordAngle {
+	if a < 0 {
+		return NegativeChordAngle
+	}
+	if a.isInf() {
+		return InfChordAngle()
+	}
+	l := 2 * math.Sin(0.5*math.Min(math.Pi, a.Radians()))
+	return ChordAngle(l * l)
+}
+
+// ChordAngleFromSquaredLength returns a ChordAngle from the squared chord length.
+// Note that the argument is automatically clamped to a maximum of 4 to
+// handle possible roundoff errors. The argument must be non-negative.
+func ChordAngleFromSquaredLength(length2 float64) ChordAngle {
+	if length2 > maxLength2 {
+		return StraightChordAngle
+	}
+	return ChordAngle(length2)
+}
+
+// Expanded returns a new ChordAngle that has been adjusted by the given error
+// bound (which can be positive or negative). Error should be the value
+// returned by either MaxPointError or MaxAngleError. For example:
+//    a := ChordAngleFromPoints(x, y)
+//    a1 := a.Expanded(a.MaxPointError())
+func (c ChordAngle) Expanded(e float64) ChordAngle {
+	// If the angle is special, don't change it. Otherwise clamp it to the valid range.
+	if c.isSpecial() {
+		return c
+	}
+	return ChordAngle(math.Max(0.0, math.Min(maxLength2, float64(c)+e)))
+}
+
+// Angle converts this ChordAngle to an Angle.
+func (c ChordAngle) Angle() Angle {
+	if c < 0 {
+		return -1 * Radian
+	}
+	if c.isInf() {
+		return InfAngle()
+	}
+	return Angle(2 * math.Asin(0.5*math.Sqrt(float64(c))))
+}
+
+// InfChordAngle returns a chord angle larger than any finite chord angle.
+// The only valid operations on an InfChordAngle are comparisons, Angle
+// conversions, and Successor/Predecessor.
+func InfChordAngle() ChordAngle {
+	return ChordAngle(math.Inf(1))
+}
+
+// isInf reports whether this ChordAngle is infinite.
+func (c ChordAngle) isInf() bool {
+	return math.IsInf(float64(c), 1)
+}
+
+// isSpecial reports whether this ChordAngle is one of the special cases.
+func (c ChordAngle) isSpecial() bool {
+	return c < 0 || c.isInf()
+}
+
+// isValid reports whether this ChordAngle is valid or not.
+func (c ChordAngle) isValid() bool {
+	return (c >= 0 && c <= maxLength2) || c.isSpecial()
+}
+
+// Successor returns the smallest representable ChordAngle larger than this one.
+// This can be used to convert a "<" comparison to a "<=" comparison.
+//
+// Note the following special cases:
+//   NegativeChordAngle.Successor == 0
+//   StraightChordAngle.Successor == InfChordAngle
+//   InfChordAngle.Successor == InfChordAngle
+func (c ChordAngle) Successor() ChordAngle {
+	if c >= maxLength2 {
+		return InfChordAngle()
+	}
+	if c < 0 {
+		return 0
+	}
+	return ChordAngle(math.Nextafter(float64(c), 10.0))
+}
+
+// Predecessor returns the largest representable ChordAngle less than this one.
+//
+// Note the following special cases:
+//   InfChordAngle.Predecessor == StraightChordAngle
+//   ChordAngle(0).Predecessor == NegativeChordAngle
+//   NegativeChordAngle.Predecessor == NegativeChordAngle
+func (c ChordAngle) Predecessor() ChordAngle {
+	if c <= 0 {
+		return NegativeChordAngle
+	}
+	if c > maxLength2 {
+		return StraightChordAngle
+	}
+
+	return ChordAngle(math.Nextafter(float64(c), -10.0))
+}
+
+// MaxPointError returns the maximum error size for a ChordAngle constructed
+// from 2 Points x and y, assuming that x and y are normalized to within the
+// bounds guaranteed by s2.Point.Normalize. The error is defined with respect to
+// the true distance after the points are projected to lie exactly on the sphere.
+func (c ChordAngle) MaxPointError() float64 {
+	// There is a relative error of (2.5*dblEpsilon) when computing the squared
+	// distance, plus a relative error of 2 * dblEpsilon, plus an absolute error
+	// of (16 * dblEpsilon**2) because the lengths of the input points may differ
+	// from 1 by up to (2*dblEpsilon) each. (This is the maximum error in Normalize).
+	return 4.5*dblEpsilon*float64(c) + 16*dblEpsilon*dblEpsilon
+}
+
+// MaxAngleError returns the maximum error for a ChordAngle constructed
+// as an Angle distance.
+func (c ChordAngle) MaxAngleError() float64 {
+	return dblEpsilon * float64(c)
+}
+
+// Add adds the other ChordAngle to this one and returns the resulting value.
+// This method assumes the ChordAngles are not special.
+func (c ChordAngle) Add(other ChordAngle) ChordAngle {
+	// Note that this method (and Sub) is much more efficient than converting
+	// the ChordAngle to an Angle and adding those and converting back. It
+	// requires only one square root plus a few additions and multiplications.
+
+	// Optimization for the common case where b is an error tolerance
+	// parameter that happens to be set to zero.
+	if other == 0 {
+		return c
+	}
+
+	// Clamp the angle sum to at most 180 degrees.
+	if c+other >= maxLength2 {
+		return StraightChordAngle
+	}
+
+	// Let a and b be the (non-squared) chord lengths, and let c = a+b.
+	// Let A, B, and C be the corresponding half-angles (a = 2*sin(A), etc).
+	// Then the formula below can be derived from c = 2 * sin(A+B) and the
+	// relationships   sin(A+B) = sin(A)*cos(B) + sin(B)*cos(A)
+	//                 cos(X) = sqrt(1 - sin^2(X))
+	x := float64(c * (1 - 0.25*other))
+	y := float64(other * (1 - 0.25*c))
+	return ChordAngle(math.Min(maxLength2, x+y+2*math.Sqrt(x*y)))
+}
+
+// Sub subtracts the other ChordAngle from this one and returns the resulting
+// value. This method assumes the ChordAngles are not special.
+func (c ChordAngle) Sub(other ChordAngle) ChordAngle {
+	if other == 0 {
+		return c
+	}
+	if c <= other {
+		return 0
+	}
+	x := float64(c * (1 - 0.25*other))
+	y := float64(other * (1 - 0.25*c))
+	return ChordAngle(math.Max(0.0, x+y-2*math.Sqrt(x*y)))
+}
+
+// Sin returns the sine of this chord angle. This method is more efficient
+// than converting to Angle and performing the computation.
+func (c ChordAngle) Sin() float64 {
+	return math.Sqrt(c.Sin2())
+}
+
+// Sin2 returns the square of the sine of this chord angle.
+// It is more efficient than Sin.
+func (c ChordAngle) Sin2() float64 {
+	// Let a be the (non-squared) chord length, and let A be the corresponding
+	// half-angle (a = 2*sin(A)). The formula below can be derived from:
+	//   sin(2*A) = 2 * sin(A) * cos(A)
+	//   cos^2(A) = 1 - sin^2(A)
+	// This is much faster than converting to an angle and computing its sine.
+	return float64(c * (1 - 0.25*c))
+}
+
+// Cos returns the cosine of this chord angle. This method is more efficient
+// than converting to Angle and performing the computation.
+func (c ChordAngle) Cos() float64 {
+	// cos(2*A) = cos^2(A) - sin^2(A) = 1 - 2*sin^2(A)
+	return float64(1 - 0.5*c)
+}
+
+// Tan returns the tangent of this chord angle.
+func (c ChordAngle) Tan() float64 {
+	return c.Sin() / c.Cos()
+}
+
+// TODO(roberts): Differences from C++:
+//   Helpers to/from E5/E6/E7
+//   Helpers to/from degrees and radians directly.
+//   FastUpperBoundFrom(angle Angle)