public double GetArea()
{
// the normal can be taken from the product of two segments on the polyline
if (Count() < 3)
{
return(double.NaN);
}
var normal = Normal() * -1;
var firstSegment = FirstSegment();
var up = XbimVector3D.CrossProduct(normal, firstSegment);
var campos = new XbimVector3D(
_geomPoints[0].Point.X,
_geomPoints[0].Point.Y,
_geomPoints[0].Point.Z
);
var target = campos + normal;
var m = XbimMatrix3D.CreateLookAt(campos, target, up);
var point = new XbimPoint3D[Count()];
for (var i = 0; i < point.Length; i++)
{
var pBefore = new XbimPoint3D(
_geomPoints[i].Point.X,
_geomPoints[i].Point.Y,
_geomPoints[i].Point.Z
);
var pAft = m.Transform(pBefore);
point[i] = pAft;
}
// http://stackoverflow.com/questions/2553149/area-of-a-irregular-shape
// it assumes that the last point is NOT the same of the first one, but it tolerates the case.
double area = 0.0f;
var numVertices = Count();
for (var i = 0; i < numVertices - 1; ++i)
{
area += point[i].X * point[i + 1].Y - point[i + 1].X * point[i].Y;
}
area += point[numVertices - 1].X * point[0].Y - point[0].X * point[numVertices - 1].Y;
area /= 2.0;
return(area);
}