/// <summary>
/// Adds an offset curve for a polygon ring.
/// The side and left and right topological location arguments
/// assume that the ring is oriented CW.
/// If the ring is in the opposite orientation,
/// the left and right locations must be interchanged and the side flipped.
/// </summary>
/// <param name="coord">The coordinates of the ring (must not contain repeated points).</param>
/// <param name="offsetDistance">The distance at which to create the buffer.</param>
/// <param name="side">The side of the ring on which to construct the buffer line.</param>
/// <param name="cwLeftLoc">The location on the L side of the ring (if it is CW).</param>
/// <param name="cwRightLoc">The location on the R side of the ring (if it is CW).</param>
private void AddRingSide(Coordinate[] coord, double offsetDistance,
Position side, Location cwLeftLoc, Location cwRightLoc)
{
// don't bother adding ring if it is "flat" and will disappear in the output
if (offsetDistance == 0.0 && coord.Length < LinearRing.MinimumValidSize)
{
return;
}
var leftLoc = cwLeftLoc;
var rightLoc = cwRightLoc;
/*
* Use area-based orientation test,
* to ensure that for invalid rings the largest enclosed area
* is used to determine orientation.
* This produces a more sensible result especially when
* used for validifying polygonal geometry via buffer-by-zero.
* For buffering use, the lower robustness of ccw-by-area
* doesn't matter, since very narrow or flat rings
* produce an acceptable offset curve for either orientation.
*/
if (coord.Length >= LinearRing.MinimumValidSize &&
Orientation.IsCCWArea(coord))
{
leftLoc = cwRightLoc;
rightLoc = cwLeftLoc;
side = side.Opposite;
}
var curve = _curveBuilder.GetRingCurve(coord, side, offsetDistance);
AddCurve(curve, leftLoc, rightLoc);
}
private void InitSideSegments(Coordinate s1, Coordinate s2, Position side)
{
_s1 = s1;
_s2 = s2;
_side = side;
_seg1.SetCoordinates(s1, s2);
ComputeOffsetSegment(_seg1, side, _distance, _offset1);
}
/// <summary>
/// Compute an offset segment for an input segment on a given side and at a given distance.
/// The offset points are computed in full double precision, for accuracy.
/// </summary>
/// <param name="seg">The segment to offset</param>
/// <param name="side">The side of the segment (<see cref="Positions"/>) the offset lies on</param>
/// <param name="distance">The offset distance</param>
/// <param name="offset">The points computed for the offset segment</param>
private static void ComputeOffsetSegment(LineSegment seg, Position side, double distance, LineSegment offset)
{
int sideSign = side == Position.Left ? 1 : -1;
double dx = seg.P1.X - seg.P0.X;
double dy = seg.P1.Y - seg.P0.Y;
double len = Math.Sqrt(dx * dx + dy * dy);
// u is the vector that is the length of the offset, in the direction of the segment
double ux = sideSign * distance * dx / len;
double uy = sideSign * distance * dy / len;
offset.P0.X = seg.P0.X - uy;
offset.P0.Y = seg.P0.Y + ux;
offset.P1.X = seg.P1.X - uy;
offset.P1.Y = seg.P1.Y + ux;
}
/// <summary>
/// This method handles the degenerate cases of single points and lines,
/// as well as rings.
/// </summary>
/// <returns>A Coordinate array representing the curve<br/>
/// or <c>null</c> if the curve is empty</returns>
public Coordinate[] GetRingCurve(Coordinate[] inputPts, Position side, double distance)
{
_distance = distance;
if (inputPts.Length <= 2)
{
return(GetLineCurve(inputPts, distance));
}
// optimize creating ring for for zero distance
if (distance == 0.0)
{
return(CopyCoordinates(inputPts));
}
var segGen = GetSegmentGenerator(distance);
ComputeRingBufferCurve(inputPts, side, segGen);
return(segGen.GetCoordinates());
}
/// <summary>
/// To compute the summary label for a side, the algorithm is:
/// FOR all edges
/// IF any edge's location is Interior for the side, side location = Interior
/// ELSE IF there is at least one Exterior attribute, side location = Exterior
/// ELSE side location = Null
/// Note that it is possible for two sides to have apparently contradictory information
/// i.e. one edge side may indicate that it is in the interior of a point, while
/// another edge side may indicate the exterior of the same point. This is
/// not an incompatibility - GeometryCollections may contain two Polygons that touch
/// along an edge. This is the reason for Interior-primacy rule above - it
/// results in the summary label having the Geometry interior on both sides.
/// </summary>
/// <param name="geomIndex"></param>
/// <param name="side"></param>
private void ComputeLabelSide(int geomIndex, Position side)
{
foreach (var e in _edgeEnds)
{
if (e.Label.IsArea())
{
var loc = e.Label.GetLocation(geomIndex, side);
if (loc == Location.Interior)
{
Label.SetLocation(geomIndex, side, Location.Interior);
return;
}
if (loc == Location.Exterior)
{
Label.SetLocation(geomIndex, side, Location.Exterior);
}
}
}
}
/// <summary>
/// This method handles the degenerate cases of single points and lines, as well as rings.
/// </summary>
/// <returns>a List of Coordinate[]</returns>
public IList <Coordinate[]> GetRingCurve(Coordinate[] inputPts, Position side, double distance)
{
var lineList = new List <Coordinate[]>();
Init(distance);
if (inputPts.Length <= 2)
{
return(GetLineCurve(inputPts, distance));
}
// optimize creating ring for for zero distance
if (distance == 0.0)
{
lineList.Add(CopyCoordinates(inputPts));
return(lineList);
}
ComputeRingBufferCurve(inputPts, side);
lineList.Add(_vertexList.Coordinates);
return(lineList);
}
private void ComputeRingBufferCurve(Coordinate[] inputPts, Position side)
{
// simplify input line to improve performance
double distTol = SimplifyTolerance(_distance);
// ensure that correct side is simplified
if (side == Position.Right)
{
distTol = -distTol;
}
var simp = BufferInputLineSimplifier.Simplify(inputPts, distTol);
// Coordinate[] simp = inputPts;
int n = simp.Length - 1;
InitSideSegments(simp[n - 1], simp[0], side);
for (int i = 1; i <= n; i++)
{
bool addStartPoint = i != 1;
AddNextSegment(simp[i], addStartPoint);
}
_vertexList.CloseRing();
}
private void ComputeRingBufferCurve(Coordinate[] inputPts, Position side, OffsetSegmentGenerator segGen)
{
// simplify input line to improve performance
double distTol = SimplifyTolerance(_distance);
// ensure that correct side is simplified
if (side == Position.Right)
{
distTol = -distTol;
}
var simp = BufferInputLineSimplifier.Simplify(inputPts, distTol);
// MD - used for testing only (to eliminate simplification)
// Coordinate[] simp = inputPts;
int n = simp.Length - 1;
segGen.InitSideSegments(simp[n - 1], simp[0], side);
for (int i = 1; i <= n; i++)
{
bool addStartPoint = i != 1;
segGen.AddNextSegment(simp[i], addStartPoint);
}
segGen.CloseRing();
}
