Offset Method (IGeometryEngine)

In This Topic

Constructs the offset version of the input geometry. The offset operation creates a geometry that is a constant distance from an input polyline or polygon. It is similar to buffering, but produces a one sided result. If offset distance > 0, then the offset geometry is constructed to the right of the oriented input geometry, otherwise it is constructed to the left. For a simple polygon, the orientation of outer rings is clockwise and for inner rings it is counter clockwise. So the "right side" of a simple polygon is always its inside. The bevelRatio is multiplied by the offset distance and the result determines how far a mitered offset intersection can be from the input curve before it is beveled.

Syntax

Visual Basic (Declaration)
C#

Function Offset( _
   ByVal geometry As Geometry, _
   ByVal distance As Double, _
   ByVal offsetType As OffsetType, _
   ByVal bevelRatio As Double _
) As Geometry

Geometry Offset( 
   Geometry geometry,
   double distance,
   OffsetType offsetType,
   double bevelRatio
)

Parameters

geometry: The geometry to calculate offset for. MapPoint and Multipoint are not supported.
distance: The offset distance for the geometry.
offsetType: The offset type of the offset geometry.
bevelRatio: The ratio used to produce a bevel join instead of a miter join (used only when offsetType is miter).

Return Value

The offset geometry. If the input geometry is empty, then it is returned unchanged.

Exceptions

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

Remarks

GeometryEngine Offset

Example

Calculate a geometry offset from the source

{
    List<MapPoint> linePts =
    [
      MapPointBuilderEx.CreateMapPoint(1.0, 1.0, SpatialReferences.WGS84),
  MapPointBuilderEx.CreateMapPoint(10.0, 1.0, SpatialReferences.WGS84),
];

    polyline = PolylineBuilderEx.CreatePolyline(linePts);

    Geometry g = GeometryEngine.Instance.Offset(polyline, 10, OffsetType.Square, 0);
    Polyline gResult = g as Polyline;
    // gResult.PointCount = 2
    // gResult.Points[0] = (1, -9)
    // gResult.Points[1] = (10, -9)

    g = GeometryEngine.Instance.Offset(polyline, -10, OffsetType.Round, 0.5);
    gResult = g as Polyline;
    // gResult.PointCount = 2
    // gResult.Points[0] = (1, -11
    // gResult.Points[1] = (10, 11)

    //
    // elliptic arc curve
    //
    Coordinate2D fromPt = new(2, 1);
    Coordinate2D toPt = new(1, 2);
    Coordinate2D interiorPt = new(1 + Math.Sqrt(2) / 2, 1 + Math.Sqrt(2) / 2);

    EllipticArcSegment circularArc = EllipticArcBuilderEx.CreateCircularArc(fromPt.ToMapPoint(), toPt.ToMapPoint(), interiorPt);

    polyline = PolylineBuilderEx.CreatePolyline(circularArc);
    g = GeometryEngine.Instance.Offset(polyline, -0.25, OffsetType.Miter, 0.5);
    gResult = g as Polyline;

    g = GeometryEngine.Instance.Offset(polyline, 0.25, OffsetType.Bevel, 0.5);
    gResult = g as Polyline;

    //
    //  offset for a polygon
    //
    List<MapPoint> list =
    [
      MapPointBuilderEx.CreateMapPoint(10.0, 10.0, SpatialReferences.WGS84),
    MapPointBuilderEx.CreateMapPoint(10.0, 20.0, SpatialReferences.WGS84),
    MapPointBuilderEx.CreateMapPoint(20.0, 20.0, SpatialReferences.WGS84),
    MapPointBuilderEx.CreateMapPoint(20.0, 10.0, SpatialReferences.WGS84),
  ];

    polygon = PolygonBuilderEx.CreatePolygon(list);

    g = GeometryEngine.Instance.Offset(polygon, 2, OffsetType.Square, 0);
    Polygon gPolygon = g as Polygon;

    g = GeometryEngine.Instance.Offset(polygon, -2, OffsetType.Round, 0.3);
    gPolygon = g as Polygon;

    g = GeometryEngine.Instance.Offset(polygon, -0.5, OffsetType.Miter, 0.6);
    gPolygon = g as Polygon;
  }

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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