private static List <CoordinateSequence> CreateRings(List <CoordinateSequence> sequences)
{
var closedRings = new List <CoordinateSequence>();
CoordinateSequence currentRing = null;
while (sequences.Any())
{
if (currentRing == null)
{
// start a new ring with any remaining node sequence
var lastIndex = sequences.Count - 1;
currentRing = sequences[lastIndex];
sequences.RemoveAt(lastIndex);
}
else
{
// try to continue the ring by appending a node sequence
CoordinateSequence assignedSequence = null;
foreach (CoordinateSequence sequence in sequences)
{
if (!currentRing.TryAdd(sequence))
{
continue;
}
assignedSequence = sequence;
break;
}
if (assignedSequence != null)
{
sequences.Remove(assignedSequence);
}
else
{
return(null);
}
}
// check whether the ring under construction is closed
if (currentRing != null && currentRing.IsClosed)
{
// TODO check that it isn't self-intersecting!
closedRings.Add(new CoordinateSequence(currentRing));
currentRing = null;
}
}
return(currentRing != null ? null : closedRings);
}