ConvexHull Method (IGeometryEngine)

In This Topic

Constructs the convex hull of the geometry.

Syntax

C#
Visual Basic (Declaration)

Geometry ConvexHull( 
   Geometry geometry
)

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

Parameters

geometry: The geometry to create a convex hull of.

Return Value

A geometry that represents the convex hull of the input geometry.

Exceptions

Exception	Description
System.ArgumentNullException	Geometry is null or empty.
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 = new List<MapPoint>();
list.Add(MapPointBuilderEx.CreateMapPoint(1.0, 1.0));
list.Add(MapPointBuilderEx.CreateMapPoint(1.0, 2.0));
list.Add(MapPointBuilderEx.CreateMapPoint(2.0, 2.0));
list.Add(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 = new List<MapPoint>();
polylineList.Add(MapPointBuilderEx.CreateMapPoint(1.0, 1.0));
polylineList.Add(MapPointBuilderEx.CreateMapPoint(2.0, 2.0));

// 2 point straight line
Polyline 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 = new List<MapPoint>();
funkyList.Add(MapPointBuilderEx.CreateMapPoint(1.0, 1.0));
funkyList.Add(MapPointBuilderEx.CreateMapPoint(1.5, 1.5));
funkyList.Add(MapPointBuilderEx.CreateMapPoint(1.0, 2.0));
funkyList.Add(MapPointBuilderEx.CreateMapPoint(2.0, 2.0));
funkyList.Add(MapPointBuilderEx.CreateMapPoint(1.5, 1.5));
funkyList.Add(MapPointBuilderEx.CreateMapPoint(2.0, 1.0));
funkyList.Add(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, Windows 10, Windows 8.1

Reference

IGeometryEngine Interface
IGeometryEngine Members

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