public void Segments()
{
var a = new LineString(new[] { p0, p1, p2, p3 });
var segments = a.Segments().ToList();
Assert.AreEqual(3, segments.Count);
AssertLineSegment(segments[0], p0, p1);
AssertLineSegment(segments[1], p1, p2);
AssertLineSegment(segments[2], p2, p3);
}
//http://mapcontext.com/autocarto/proceedings/auto-carto-12/pdf/computation-of-the-hausdorff-distance-between-plane.pdf
public static double Distance(LineString a, LineString b)
{
//computation of distances from the vertices of A to polyline B (need to know specific segments)
var aVertices = a.Points().ToList();
var bVertices = b.Points().ToList();
var bSegments = b.Segments().ToList();
var aSegments = a.Segments().ToList();
var closestCache = new Dictionary<IGeometry, Tuple<IGeometry, double>>();
Func<IGeometry, Tuple<IGeometry, double>> closest = p =>
{
if(!closestCache.ContainsKey(p))
{
closestCache.Add(p, ClosestGeometry(p, bVertices, bSegments));
}
return closestCache[p];
};
Func<IGeometry, IGeometry, bool> pointsAreSuccessiveVertices = (cs, ce) =>
{
var point1 = cs as IPoint;
var point2 = ce as IPoint;
return (point1 != null && point2 != null) && Math.Abs(bVertices.IndexOf(point1) - bVertices.IndexOf(point2)) == 1;
};
var verticesWithDistance = aVertices
.Select(pa =>
{
var cst = closest(pa);
return Tuple.Create(pa, cst.Item1, cst.Item2);
});
var distance = verticesWithDistance.Max(tpl => tpl.Item3);
//test to detect whether further calculation is required or a vertex of A bears the greatest distance from A to B
var needsInvestigation = aSegments
.Where(aseg =>
{
//if we can confirm distance between segments is increasing/decreasing, no need to investigate that segment
// test is that closest components for each point (segment OR vertex) are the same, or closest components are successive vertices in B
var closestToStart = closest(aseg.StartPoint).Item1;
var closestToEnd = closest(aseg.EndPoint).Item1;
return !(closestToStart == closestToEnd
|| pointsAreSuccessiveVertices(closestToStart, closestToEnd));
})
.Select(aseg =>
{
var cst = closest(aseg);
return Tuple.Create(aseg, cst.Item1, cst.Item2);
})
.ToList();
if(needsInvestigation.Count > 0) //check if a vertex doesn't bear the greatest distance
{
//and if it doesn't we need to compute the greatest distance on likely segments and reassign distance here
throw new NotImplementedException();
}
return distance;
}