ConvexHull Method (IGeometryEngine)

In This Topic

Constructs the convex hull of the geometry.

Syntax

Visual Basic (Declaration)
C#

Function ConvexHull( _
   ByVal geometry As Geometry _
) As Geometry

Geometry ConvexHull( 
   Geometry geometry
)

Parameters

geometry: The geometry to create a convex hull of.

Return Value

A polygon that represents the convex hull of the input geometry. If the input geometry is empty, then an empty polygon is returned.

Exceptions

Exception	Description
System.ArgumentNullException	Geometry is null.
System.NotImplementedException	The method is not implemented for GeometryBag.

Remarks

The convex hull of a geometry is the minimal bounding polygon such that all outer angles are convex. The ConvexHull of a point is the point itself.

GeometryEngine ConvexHull

Example

Determine convex hull

{
    //
    // convex hull around a point - returns a point
    //

    MapPoint pt = MapPointBuilderEx.CreateMapPoint(2.0, 2.0);
    Geometry hull = GeometryEngine.Instance.ConvexHull(pt);
    MapPoint hullPt = hull as MapPoint;
    // nullPt.X = 2
    // hullPt.Y = 2


    List<MapPoint> list =
    [
      MapPointBuilderEx.CreateMapPoint(1.0, 1.0),
  MapPointBuilderEx.CreateMapPoint(1.0, 2.0),
  MapPointBuilderEx.CreateMapPoint(2.0, 2.0),
  MapPointBuilderEx.CreateMapPoint(2.0, 1.0),
];

    //
    // convex hull around a multipoint - returns a polygon
    //

    // build a multiPoint
    Multipoint multiPoint = MultipointBuilderEx.CreateMultipoint(list);

    hull = GeometryEngine.Instance.ConvexHull(multiPoint);
    Polygon hullPoly = hull as Polygon;
    // hullPoly.Area = 1
    // hullPoly.PointCount = 5

    // 
    // convex hull around a line - returns a polyline or polygon
    // 

    List<MapPoint> polylineList = [MapPointBuilderEx.CreateMapPoint(1.0, 1.0), MapPointBuilderEx.CreateMapPoint(2.0, 2.0)];

    // 2 point straight line
    polyline = PolylineBuilderEx.CreatePolyline(polylineList);
    hull = GeometryEngine.Instance.ConvexHull(polyline);
    Polyline hullPolyline = hull as Polyline;
    // hullPolyline.Length = Math.Sqrt(2)
    // hullPolyline.PointCount = 2

    // 3 point angular line
    polylineList.Add(MapPointBuilderEx.CreateMapPoint(2.0, 1.0));
    polyline = PolylineBuilderEx.CreatePolyline(polylineList);
    hull = GeometryEngine.Instance.ConvexHull(polyline);
    hullPoly = hull as Polygon;
    // hullPoly.Length = 2 + Math.Sqrt(2)
    // hullPoly.Area = 0.5
    // hullPoly.PointCount = 4

    //
    // convex hull around a polygon - returns a polygon
    //

    // simple polygon
    Polygon poly = PolygonBuilderEx.CreatePolygon(list);
    hull = GeometryEngine.Instance.ConvexHull(poly);
    hullPoly = hull as Polygon;

    // hullPoly.Length = 4.0
    // hullPoly.Area = 1.0
    // hullPoly.PointCount = 5

    // polygon with concave angles
    List<MapPoint> funkyList =
    [
      MapPointBuilderEx.CreateMapPoint(1.0, 1.0),
  MapPointBuilderEx.CreateMapPoint(1.5, 1.5),
  MapPointBuilderEx.CreateMapPoint(1.0, 2.0),
  MapPointBuilderEx.CreateMapPoint(2.0, 2.0),
  MapPointBuilderEx.CreateMapPoint(1.5, 1.5),
  MapPointBuilderEx.CreateMapPoint(2.0, 1.0),
  MapPointBuilderEx.CreateMapPoint(1.0, 1.0),
];

    Polygon funkyPoly = PolygonBuilderEx.CreatePolygon(funkyList);
    hull = GeometryEngine.Instance.ConvexHull(funkyPoly);
    hullPoly = hull as Polygon;
    // hullPoly.Length = 4.0
    // hullPoly.Area = 1.0
    // hullPoly.PointCount = 5
    // hullPoly.Points[0] = 1.0, 1.0
    // hullPoly.Points[1] = 1.0, 2.0
    // hullPoly.Points[2] = 2.0, 2.0
    // hullPoly.Points[3] = 2.0, 1.0
    // hullPoly.Points[4] = 1.0, 1.0
  }

Requirements

Target Platforms: Windows 11 Home, Pro, Enterprise (64 bit)

ArcGIS Pro version: 3.0 or higher.

Reference

IGeometryEngine Interface
IGeometryEngine Members

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