/// <summary>
/// simple_Polygon(): test if a Polygon is simple or not
/// Input: Pn = a polygon with n vertices V[]
/// Return: false(0) = is NOT simple
/// true(1) = IS simple
/// </summary>
/// <param name="polygon"></param>
/// <returns></returns>
public bool IsSimple(Polygon polygon)
{
Require.ArgumentNotNull(polygon, nameof(polygon));
EventQueue eventQueue = new EventQueue(polygon);
SweepLine sweepLine = new SweepLine(polygon);
Event currentEvent; // the current event
// This loop processes all events in the sorted queue
// Events are only left or right vertices since
// No new events will be added (an intersect => Done)
while ((currentEvent = eventQueue.Next()) != null)
{
// while there are events
if (currentEvent.EventType == EventType.Left)
{ // process a left vertex
var currentSegment = sweepLine.Add(currentEvent); // add it to the sweep line
if (sweepLine.Intersect(currentSegment, currentSegment.Above))
{
return(false); // Pn is NOT simple
}
if (sweepLine.Intersect(currentSegment, currentSegment.Below))
{
return(false); // Pn is NOT simple
}
}
else
{ // processs a right vertex
var currentSegment = sweepLine.Find(currentEvent);
if (sweepLine.Intersect(currentSegment.Above, currentSegment.Below))
{
return(false); // Pn is NOT simple
}
sweepLine.Remove(currentSegment); // remove it from the sweep line
}
}
return(true); // Pn IS simple
}
/// <summary>
/// Computes whether one or more line strings specified by coordinates intersects with each other.
/// </summary>
public void Compute()
{
// source: http://geomalgorithms.com/a09-_intersect-3.html
EndPointEvent e = _eventQueue.Next();
SweepLineSegment segment;
while (e != null)
{
switch (e.Type)
{
case EventType.Left:
segment = _sweepLine.Add(e);
if (segment.Above != null && _sweepLine.IsAdjacent(segment.Edge, segment.Above.Edge) && segment.LeftCoordinate == segment.Above.LeftCoordinate)
{
_sweepLine.Intersect(segment, segment.Above);
}
else if (segment.Below != null && _sweepLine.IsAdjacent(segment.Edge, segment.Below.Edge) && segment.LeftCoordinate == segment.Below.LeftCoordinate)
{
_sweepLine.Intersect(segment, segment.Below);
}
if (segment.Above != null && !_sweepLine.IsAdjacent(segment.Edge, segment.Above.Edge) &&
LineAlgorithms.Intersects(segment.LeftCoordinate, segment.RightCoordinate,
segment.Above.LeftCoordinate, segment.Above.RightCoordinate,
PrecisionModel))
{
_hasResult = true;
_result = true;
return;
}
if (segment.Below != null && !_sweepLine.IsAdjacent(segment.Edge, segment.Below.Edge) &&
LineAlgorithms.Intersects(segment.LeftCoordinate, segment.RightCoordinate,
segment.Below.LeftCoordinate, segment.Below.RightCoordinate,
PrecisionModel))
{
_hasResult = true;
_result = true;
return;
}
break;
case EventType.Right:
segment = _sweepLine.Search(e);
if (segment != null)
{
if (segment.Above != null && segment.Below != null && !_sweepLine.IsAdjacent(segment.Below.Edge, segment.Above.Edge) &&
LineAlgorithms.Intersects(segment.Above.LeftCoordinate, segment.Above.RightCoordinate,
segment.Below.LeftCoordinate, segment.Below.RightCoordinate,
PrecisionModel))
{
_hasResult = true;
_result = true;
return;
}
_sweepLine.Remove(segment);
}
break;
}
e = _eventQueue.Next();
}
_hasResult = true;
_result = false;
}
