Is There is a way in .net to get centroid for polyline?

Question

I want to get the centroid of polyline2d. I have a polyline from TraceBoundary like so:

DBObjectCollection objs = Application.DocumentManager.MdiActiveDocument.Editor.TraceBoundary(Point, false);
Polyline polyline = (Polyline)objs[0];
Point2d centroid = ***The missing part i need any way to get center of gravity of the above polyline as point2d***

I was doing that before with autolisp:

(setq arob (entlast))
(setq enpol (vlax-ename->vla-object arob))
(setq cgpoint (vlax-get-property enpol 'Centroid))

I have a mathematical solution, but it's not valid when the polyline comes with some curves.

I won't use this function:

public static Point2d GetPolyLineCentroid(Polyline polyline)
    {
        double area = polyline.Area;
        double cx = 0.0;
        double cy = 0.0;
        double X0 = 0.0;
        double Y0 = 0.0;
        double X1 = 0.0;
        double Y1 = 0.0;

        for (int i = 0; i < polyline.NumberOfVertices - 1; i++)
        {
            X0 = polyline.GetPoint2dAt(i).X;
            Y0 = polyline.GetPoint2dAt(i).Y;
            X1 = polyline.GetPoint2dAt(i + 1).X;
            Y1 = polyline.GetPoint2dAt(i + 1).Y;

            cx += (X0 + X1) * (X0 * Y1 - X1 * Y0);
            cy += (Y0 + Y1) * (X0 * Y1 - X1 * Y0);
        }

        // last Point
        int Lv = polyline.NumberOfVertices - 1;
        X0 = polyline.GetPoint2dAt(Lv).X;
        Y0 = polyline.GetPoint2dAt(Lv).Y;
        X1 = polyline.GetPoint2dAt(0).X;
        Y1 = polyline.GetPoint2dAt(0).Y;

        cx += (X0 + X1) * (X0 * Y1 - X1 * Y0);
        cy += (Y0 + Y1) * (X0 * Y1 - X1 * Y0);


        cx /= 6 * area;
        cy /= 6 * area;

        return new Point2d(cx, cy);
    }

I don't want to use AutoLisp. Is there a way to do this in .NET?

score 2 · Accepted Answer · edited Nov 03 '11 at 08:35

2

I found this solution and it's valid for me:

public static Point2d GetPolyLineCentroid(DBObjectCollection objs)
{
    Solid3d Solid = new Solid3d();
    Solid.Extrude(((Region)Region.CreateFromCurves(objs)[0]), 1, 0);
    Point2d centroid = new Point2d(Solid.MassProperties.Centroid.X, Solid.MassProperties.Centroid.Y);
    Solid.Dispose();
    return centroid;
}

edited Nov 03 '11 at 08:35

ptomato

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answered Jul 17 '11 at 17:45

Khalid Omar

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Maxence · Answer 2 · 2016-12-21T08:55:02.543

2

For AutoCAD <= 2013, create a region with .NET (Region.CreateFromCurves), and get a reference to it with COM and the HandleToObject method. On the region ActiveX object, there is a Centroid property.

For AutoCAD > 2013, there is a AreaProperties method on the Region class that returns a RegionAreaProperties structure with a Centroid property.

edited Dec 21 '16 at 08:55

answered Aug 01 '11 at 10:28

Maxence

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@Maxence - small world it is - do you know if it's possible to get a reference to the region without using COM? – BenKoshy Dec 21 '16 at 08:10

Is There is a way in .net to get centroid for polyline?

2 Answers2