/// <summary>
/// Find elements either contained, containing or intersecting polygon.
/// <para>
/// If no elements are found, an empty list is returned.
/// </para>
/// </summary>
public IList <MeshElement> FindElements(Polygon polygon)
{
if (_elementSearchTree == null)
{
SetupElementSearch();
}
Envelope targetEnvelope = polygon.EnvelopeInternal;
IList <MeshElement> potentialElmts = _elementSearchTree.Query(targetEnvelope);
List <MeshElement> result = new List <MeshElement>();
// Loop over all potential elements
for (int i = 0; i < potentialElmts.Count; i++)
{
MeshElement element = potentialElmts[i];
// Fast-lane check: When there is no overlap even by the envelopes
if (!targetEnvelope.Intersects(element.EnvelopeInternal()))
{
continue;
}
// More detailed check for actual overlap
Polygon elementPolygon = element.ToPolygon();
if (elementPolygon.Intersects(polygon))
{
result.Add(element);
}
}
return(result);
}
/// <summary>
/// Create a polygon from a mesh element
/// </summary>
public static Polygon ToPolygon(this MeshElement element)
{
return(element.ToPolygon(GeomFactory));
}
/// <summary>
/// Find elements either contained, containing or intersecting the polygon.
/// <para>
/// This method can be used if only some elements of the mesh is to be included
/// in the weight calculations.
/// </para>
/// <para>
/// If polygon is totally contained within one mesh element, then 1 element is returned.
/// If polygon partially falls outside of the grid, only elements within grid are returned.
/// </para>
/// <param name="polygon">Polygon or multi-polygon</param>
/// <param name="elements">List of elements</param>
/// </summary>
public List <ElementWeight> CalculateWeights(Geometry polygon, IList <MeshElement> elements)
{
Envelope targetEnvelope = polygon.EnvelopeInternal;
//// It should be faster to use than the polygon directly?
//PreparedPolygon prepolygon = new PreparedPolygon(polygon);
List <ElementWeight> result = new List <ElementWeight>();
// Total intersecting area
double totalArea = 0;
// Loop over all potential elements
for (int i = 0; i < elements.Count; i++)
{
MeshElement element = elements[i];
// Fast-lane check: When there is no overlap even by the envelopes
if (!targetEnvelope.Intersects(element.EnvelopeInternal()))
{
continue;
}
Polygon elementPolygon = element.ToPolygon();
Geometry intersection = elementPolygon.Intersection(polygon);
if (!intersection.IsEmpty)
{
// Target polygon and element polygon has an overlap.
// If target polygon fully contains the element polygon, this is the element area
// If element polygon fully contains the target polygon, this is the polygon area
double intersectingArea = intersection.Area;
totalArea += intersectingArea;
if (WeightType == WeightType.Fraction)
{
result.Add(new ElementWeight(element, intersectingArea / elementPolygon.Area));
}
else
{
result.Add(new ElementWeight(element, intersectingArea));
}
}
}
IntersectionArea = totalArea;
if (result.Count == 0 || totalArea == 0)
{
return(null);
}
// When Weight-based calculations, weight with the total intersecting area
if (WeightType == WeightType.Weight)
{
for (int i = 0; i < result.Count; i++)
{
ElementWeight elmtWeight = result[i];
elmtWeight.Weight /= totalArea;
result[i] = elmtWeight;
}
}
return(result);
}