/// <summary>
/// Returns a list of interpolated points or null.
/// </summary>
/// <param name="samplingRate">The sampling rate should more then two.</param>
/// <param name="path">The original list of points.</param>
/// <returns>A list of points or null if the sampling rate is to small.</returns>
public IList<Vector3D> Interpolate(UInt16 samplingRate, IList<Vector3D> path)
{
if (path == null || path.Count < 3)
return null;
if (samplingRate < 2)
return null;
_samplingRate = samplingRate;
_path = path;
var interpolatedPath = new Vector3D[_samplingRate];
// The aim is to produce sampling rate - 1 line segments - in other words
// as many points as the sampling rate value.
_sampleLength = TotalPathDistance() / (_samplingRate - 1);
// Keep the first and last point of the original path.
interpolatedPath[0] = path[0];
interpolatedPath[samplingRate-1] = path[path.Count-1];
// Pre-calculate distances from start for all points in the original path.
var pathDistances = new double[path.Count];
for (int i = 1; i < pathDistances.Length; i++)
{
pathDistances[i] = pathDistances[i-1] + (path[i] - path[i - 1]).Length;
}
int pathIndex = 1;
for (int i = 1; i < interpolatedPath.Length; i++)
{
// Find the first index of the original path whose distance is greater
// than that of the next sample we have to place on the path.
while (i * _sampleLength > pathDistances[pathIndex])
{
pathIndex++;
}
// Calculate fraction of new sample within step of original path.
var fraction = _sampleLength - (pathDistances[pathIndex - 1] - ((i - 1)*_sampleLength));
var direction = path[pathIndex] - path[pathIndex - 1];
direction.Normalize();
var offset = Vector3D.Multiply(direction, fraction);
interpolatedPath[i] = Vector3D.Add(path[pathIndex-1], offset);
}
return interpolatedPath.ToList();
}
