/// <summary>
/// Bounce a platform around inside a given perimeter
/// </summary>
/// <param name="perimeter">A GeoArray of points in the perimeter, which must satisfy certain conditions (no segments may cross and the polygon
/// must be closed)</param>
/// <param name="startPoint">A Geo containing the starting point. If this is null, a point inside the perimeter is chosen randomly</param>
/// <param name="initialCourse">The initial course, in radians from true north. If startPoint is null, or if initialCourse is NaN, this is
/// chosen randomly</param>
/// <param name="minimumCourseLength">The minimum length of the returned course, in meters</param>
/// <returns>A GeoArray containing the start location and each point where the course bounces off the perimeter</returns>
public static GeoArray PerimeterBounce(this GeoArray perimeter, Geo startPoint, double initialCourse, double minimumCourseLength)
{
if (!perimeter.IsClosed) throw new InvalidPerimeterException("Perimeter is not closed");
if (perimeter.HasCrossingSegments) throw new InvalidPerimeterException("Perimeter is not a simple polygon (segments cross each other)");
var points = new List<Geo>();
while ((startPoint == null) || (!startPoint.IsInside(perimeter)))
{
var distance = Random.NextDouble() * perimeter.BoundingCircle.Radius;
var azimuth = Random.NextDouble() * MoreMath.TwoPi;
startPoint = perimeter.Center.Offset(distance, azimuth);
}
points.Add(startPoint);
if (double.IsNaN(initialCourse)) initialCourse = Random.NextDouble()*MoreMath.TwoPi;
var courseSegment = new GeoSegment(startPoint, startPoint.Offset(Geo.KilometersToRadians(0.001), initialCourse)).Scale(1000 * Geo.RadiansToKilometers(MoreMath.PiOverTwo));
var bounceCount = 1;
while (minimumCourseLength > 0)
{
var minIntersectionRange = double.MaxValue;
GeoSegment firstIntersectingSegment = null;
Geo firstIntersection = null;
foreach (var segment in perimeter.Segments)
{
var intersection = courseSegment.Intersection(segment);
if (intersection == null) continue;
var curIntersectionRange = startPoint.DistanceRadians(intersection);
if (curIntersectionRange < Geo.KilometersToRadians(0.001) || curIntersectionRange >= minIntersectionRange) continue;
minIntersectionRange = curIntersectionRange;
firstIntersectingSegment = segment;
firstIntersection = intersection;
}
if (firstIntersection == null) throw new PerimeterBounceException(string.Format("Course segment failed to intersect the perimeter on bounce {0}", bounceCount));
var actualCourseSegment = new GeoSegment(points.Last(), firstIntersection);
minimumCourseLength -= Geo.RadiansToKilometers(actualCourseSegment.LengthRadians) * 1000;
points.Add(firstIntersection);
var reflectedSegment = courseSegment.Reflect(firstIntersectingSegment);
var reflectionAzimuth = reflectedSegment[0].Azimuth(reflectedSegment[1]);
courseSegment = new GeoSegment(reflectedSegment[1], 1000 * Geo.RadiansToKilometers(MoreMath.PiOverTwo), Geo.RadiansToDegrees(reflectionAzimuth));
bounceCount++;
}
return new GeoArray(points);
}
public static bool Contains(this GeoArray region, Geo p)
{
return p.IsInside(region);
}
