/// <summary>
/// Gets the point on this line that is closest to a specified position.
/// </summary>
/// <param name="p">The position to search from.</param>
/// <param name="tol">Maximum distance from line to the search position</param>
/// <param name="doLast">Specify true to consider the last segment. False to ignore the
/// last segment.</param>
/// <returns>The closest position (null if the line is further away than the specified
/// max distance)</returns>
IPosition FindClosest(IPointGeometry p, ILength tol, bool doLast)
{
IPointGeometry[] data = Data;
// Initial "best" distance squared cannot be greater than the square of the match tolerance.
double tm = tol.Meters;
double bestdsq = tm * tm;
// Best segment number so far (valid segment numbers start at 1).
int best = 0;
// Pull out the XY of the search vertex
double vx = p.X;
double vy = p.Y;
// Get start of the initial line segment
double x1 = data[0].X;
double y1 = data[0].Y;
// Only do the last segment when required.
int nv = data.Length;
if (!doLast)
{
nv--;
}
for (int i = 1; i < nv; i++)
{
// Pick up the end of the segment & get the window of
// the segment, expanded by the match tolerance.
double x2 = data[i].X;
double y2 = data[i].Y;
double xmin = Math.Min(x1, x2) - tm;
double ymin = Math.Min(y1, y2) - tm;
double xmax = Math.Max(x1, x2) + tm;
double ymax = Math.Max(y1, y2) + tm;
// If the search vertex falls within the expanded window,
// and the distance (squared) to the perpendicular point
// is better than what we already got, remember the index
// number of this segment.
if (vx > xmin && vx < xmax && vy > ymin && vy < ymax)
{
double dsq = Geom.DistanceSquared(vx, vy, x1, y1, x2, y2);
if (dsq < bestdsq)
{
bestdsq = dsq;
best = i;
}
}
// End of segment is start of next one
x1 = x2;
y1 = y2;
}
// Return if we did not locate a suitable point
if (best == 0)
{
return(null);
}
// Get the position of the perpendicular point.
double xp, yp;
IPointGeometry s = data[best - 1];
IPointGeometry e = data[best];
Geom.GetPerpendicular(vx, vy, s.X, s.Y, e.X, e.Y, out xp, out yp);
return(new Position(xp, yp));
}