func CapFromCenterAngle(center Point, angle s1.Angle) Cap {
	return CapFromCenterChordAngle(center, s1.ChordAngleFromAngle(angle))
}
CapFromCenterAngle constructs a cap with the given center and angle.
package s2
import (
	"fmt"
	"io"
	"math"
	"github.com/golang/geo/r1"
	"github.com/golang/geo/s1"
)
var (
	centerPoint = PointFromCoords(1.0, 0, 0)
)
type Cap struct {
	center Point
	radius s1.ChordAngle
}
func CapFromPoint(p Point) Cap {
	return CapFromCenterChordAngle(p, 0)
}