/// <summary>
/// For faster clipping of polygons with lines. Limits the finding of intersections to
/// outside->inside or inside->outside 2pt segments. Assumes only one intersections exists
/// per segment, that a segment of two inside points or two outside points will not intersect
/// the polygon.
/// </summary>
/// <param name="polygon">The polygon that will be sectioned by the line.</param>
/// <param name="line">The line that will clip the polygon into multiple parts.</param>
/// <param name="resultFeatureSet">The in-memory shapefile where the polygon sections will be saved.</param>
/// <returns>False if errors are encountered, true otherwise.</returns>
public static bool Fast_ClipPolygonWithLine(
ref IFeature polygon, ref IFeature line, ref IFeatureSet resultFeatureSet)
{
IFeatureSet resultFile = new FeatureSet(FeatureType.Polygon);
if (polygon != null && line != null)
{
// make sure we are dealing with a valid shapefile type
if (polygon.FeatureType == FeatureType.Polygon)
{
// create the result shapefile if it does not already exist
if (!polygon.Overlaps(line))
{
resultFeatureSet = resultFile;
return false;
}
// find if all of the line is inside, outside, or part in and out of polygon
// line might intersect polygon mutliple times
int numPoints = line.NumPoints;
bool[] ptsInside = new bool[numPoints];
int numInside = 0;
int numOutside = 0;
int numParts = polygon.NumGeometries;
if (numParts == 0)
{
numParts = 1;
}
Coordinate[][] polyVertArray = new Coordinate[numParts][];
ConvertPolyToVertexArray(ref polygon, ref polyVertArray);
// check each point in the line to see if the entire line is either
// inside of the polygon or outside of it (we know it's inside polygon bounding box).
for (int i = 0; i <= numPoints - 1; i++)
{
Point currPt = new Point(line.Coordinates[i]);
if (polygon.Covers(currPt))
{
ptsInside[i] = true;
numInside += 1;
}
else
{
ptsInside[i] = false;
numOutside += 1;
}
}
// case: all points are inside polygon - check for possible intersections
if (numInside == numPoints)
{
// assume no intersections exist in fast version
}
else if (numOutside == numPoints)
{
// case: all points are outside of the polygon - check for possible intersections
// assume no intersections exist in fast version
}
else
{
// case: part of line is inside and part is outside - find inside segments.
if (Fast_ProcessPartInAndOut(ptsInside, line, polygon, resultFile) == false)
{
resultFeatureSet = resultFile;
return false;
}
}
// resultSF result file, do not save to disk.
resultFeatureSet = resultFile;
}
else
{
resultFeatureSet = resultFile;
return false;
}
}
else
{
// polygon or line is invalid
resultFeatureSet = resultFile;
return false;
}
return true;
}
