/// <summary>
/// Determines which side of a divider a horizontal line segment lies on.
/// Used in point in polygon.
/// </summary>
/// <param name="id">The divider to process</param>
/// <param name="s">Start of horizontal segment.</param>
/// <param name="e">End of segment.</param>
/// <param name="od">The divider the side refers to. This usually refers to
/// the supplied divider, but may refer to another divider in a situation where the
/// horizontal segment passes directly through one end of <paramref name="d"/>.</param>
/// <returns>Side.Left if the line is to the left of the divider, Side.Right
/// if line to the right, Side.On if the end of the line is coincident with
/// the divider, Side.Unknown if an error arose.</returns>
/// <remarks>
/// Rather than passing in 2 PointGeometry objects, it would be better to pass
/// in a HorizontalRay object, since 2 arbitrary positions are not guaranteed
/// to be horizontal.
/// </remarks>
internal static Side GetSide(IDivider id, IPointGeometry s, IPointGeometry e, out IDivider od)
{
// If the end of the horizontal segment hits the start or
// the end of the specified divider, we have a situation where the divider
// may not be the divider which is adjacent to the segment. In
// that case, use special code to determine the side code.
// Otherwise just convert the supplied divider into a line, and get the
// side code by looking for a vertex which has a different
// northing from that of the horizontal segment.
Debug.Assert(s.Easting.Microns <= e.Easting.Microns);
double d = e.Easting.Meters - s.Easting.Meters;
Debug.Assert(d>=0.0);
HorizontalRay hseg = new HorizontalRay(s, d);
if (e.IsCoincident(id.From) || e.IsCoincident(id.To)) // e both times!
return hseg.GetSide(id, e.IsCoincident(id.From), out od);
else
{
od = id;
return od.LineGeometry.GetSide(hseg);
}
}
