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Hi,
You have to clarify what you mean with: "sort point of a polygon".
Are the point list you provided the polygon vertices?
If so, you cannot change their order (except reversing them) without modifiing the polygon shape (and its area).
If not, you have to explain further the relation between this point list and the polygon you expect.
If your point list describe the polygon vertices, you can get the signed polygon area (positive if points are CCW negative if they're CW) with the following code.
public double PolygonSignedArea(Point2d[] points)
{
Point2d p0 = points[0];
double area = 0.0;
double triangleSignedArea(Point2d p1, Point2d p2) =>
(p1.X - p0.X) * (p2.Y - p0.Y) - (p2.X - p0.X) * (p1.Y - p0.Y);
for (int i = 0; i < points.Length - 1; i++)
{
area += triangleSignedArea(points[i], points[i + 1]);
}
return area / 2.0;
}
I do not understand what objective criteria allow you to retain certain points and to exclude others.
For example, a 2D convex hull would have followed the green line (here's a code code to get the convex hull from a point list).
Thanks , very grateful you have enthusiastically helped me,
I am using civil3d, i get the promiscuous point list from materialsection, I am looking to take the area of this point list
Ok,
To get the "boundary point list", you can use the following ConvexHull() method passing it the "point list from section".
You ca then get the "area" using the PolygonSignedArea() method passing it the point list returned by ConvexHull().
double area = PolygonSignedArea(ConvexHull(pointListFromSection));
public List<Point2d> ConvexHull(IEnumerable<Point2d> source)
{
var p0 = source.OrderBy(p => p.Y).ThenBy(p => p.X).First();
bool Clockwise(Point2d p1, Point2d p2, Point2d p3) =>
DoubleSignedArea(p1, p2, p3) < 1e-9;
double Cosine(Point2d pt)
{
double d = p0.GetDistanceTo(pt);
return d == 0.0 ? 1.0 : Math.Round((pt.X - p0.X) / d, 9);
}
var pts = source.OrderByDescending(p => Cosine(p)).ThenBy(p => p0.GetDistanceTo(p)).ToList();
for (int i = 1; i < pts.Count - 1; i++)
{
while (i > 0 && Clockwise(pts[i - 1], pts[i], pts[i + 1]))
{
pts.RemoveAt(i);
i--;
}
}
return pts;
}
public double PolygonSignedArea(IEnumerable<Point2d> source)
{
var points = source.ToArray();
Point2d p0 = points[0];
double area = 0.0;
for (int i = 0; i < points.Length - 1; i++)
{
area += DoubleSignedArea(p0, points[i], points[i + 1]);
}
return area / 2.0;
}
private double DoubleSignedArea(Point2d p1, Point2d p2, Point2d p3) =>
(p2.X - p1.X) * (p3.Y - p1.Y) - (p2.Y - p1.Y) * (p3.X - p1.X);
Hi,
@mohamed.adel.ghazaly a écrit :
order points clock wise without excluding any even the inside points
This doesn't mean much if you don't specify a reference point. For example, depending on which point you start from (the lowest, the highest, the leftmost), the results are different.
@mohamed.adel.ghazaly this should work:
static Point3dCollection SortPointsClockwise(Point3dCollection points)
{
var result = new Point3dCollection();
var topMost = points.Cast<Point3d>().Aggregate((p1, p2) => p1.Y < p2.Y ? p2 : p1);
points.Remove(topMost);
result.Add(topMost);
foreach (var pt in points
.Cast<Point3d>()
.OrderBy(p => Vector3d.XAxis.GetAngleTo(topMost.GetVectorTo(p))))
{
result.Add(pt);
}
return result;
}
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