QueryTangent(Segment,SegmentExtension,Double,AsRatioOrLength,Double) Method

Constructs a line tangent to a segment from a point at a specified distance along the segment.

Syntax

C#
Visual Basic (Declaration)

LineSegment QueryTangent( 
   Segment segment,
   SegmentExtension extension,
   double distanceAlongCurve,
   AsRatioOrLength asRatioOrLength,
   double tangentLength
)

Overloads Function QueryTangent( _
   ByVal segment As Segment, _
   ByVal extension As SegmentExtension, _
   ByVal distanceAlongCurve As Double, _
   ByVal asRatioOrLength As AsRatioOrLength, _
   ByVal tangentLength As Double _
) As LineSegment

Parameters

segment: The segment to which the tangent line is constructed.
extension: Specifies the extension method that determines the direction and position of the tangent line.
distanceAlongCurve: Specifies the distance along the segment from which the tangent line is constructed.
asRatioOrLength: Determines whether the distanceAlongCurve is returned as a ratio of the segment length or as length from the start point.
tangentLength: Specifies the length of the returned tangent line.

Return Value

LineSegment representing the tangent line.

Exceptions

Exception	Description
System.ArgumentNullException	segmentis null.
System.NotImplementedException	Spatial reference of segmentis an image coordinate system.

Remarks

The returned tangent line is in the same direction of the input segment. The distanceAlongCurve parameter can be negative, and it can be larger than the length of the segment. The extension parameter is ignored if distanceAlongCurve is greater than zero and less than the length of the segment. For example, shown below in blue is an elliptic arc segment with its start point in green and end point in red. The orange tangent line is constructed halfway along the curve, and the extension parameter is ignored.

QueryTangent_NoExtensionHalfway

If distanceAlongCurve is less than zero, then the tangent line is embedded in an extension from the start point of the segment. In the following example, distanceAlongCurve = -1.2, asRatioOrLength = AsRatioOrLength.AsRatio, and extension = SegmentExtension.ExtendTangentAtFrom. The extended tangent segment is the gray dashed line and is 1.2 * length of the input segment. The constructed tangent is in orange.

QueryTangent_TangentAtFromNegative

If distanceAlongCurve is greater than the length of the input segment, then the tangent line is embedded in an extension from the end point of the segment. In the following example, distanceAlongCurve = 1.2, asRatioOrLength = AsRatioOrLength.AsRatio, and extension = SegmentExtension.ExtendTangentAtTo. Note that if asRatioOrLength = AsRatioOrLength.AsRatio, then the length of the input segment is 1. The extended tangent segment is the gray dashed line and is 0.2 * length of the input segment. The constructed tangent is in orange.

QueryTangent_TangentAtToPositive

SegmentExtension.ExtendEmbeddedAtTo, SegmentExtension.ExtendEmbeddedAtFrom, and SegmentExtension.ExtendEmbedded when applied to an elliptic arc segment refer to the embedded ellipse or circle. Shown below in blue is an elliptic arc segment that is circular along with its embedded circle in gray.

QueryTangent_ArcWithEmbeddedCircle

Here is an example where distanceAlongCurve = 1.2, asRatioOrLength = AsRatioOrLength.AsRatio, and extension = SegmentExtension.ExtendEmbeddedAtTo.

QueryTangent_EmbeddedAtToPositive

If the input segment is not an elliptic arc segment, then SegmentExtension.ExtendEmbeddedAtTo, SegmentExtension.ExtendEmbeddedAtFrom, and SegmentExtension.ExtendEmbedded are equivalent to SegmentExtension.ExtendTangentAtTo, SegmentExtension.ExtendTangentAtFrom, and SegmentExtension.ExtendTangent respectively. There are cases when the tangent cannot be extended as specified by the extension parameter. For example, if the distanceAlongCurve is negative and extension = SegmentExtension.ExtendTangentAtTo. In this case, the tangent line is constructed at the start point of the input segment. Similarly, if the distanceAlongCurve is greater than the length of the input segment and extension = SegmentExtension.ExtendTangentAtFrom, then the tangent line is constructed at the end point of the input segment.

Example

LineSegment line = LineBuilder.CreateLineSegment(new Coordinate2D(0, 0), new Coordinate2D(1, 0));

// No extension, distanceAlongCurve = 0.5
LineSegment tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtension.NoExtension, 0.5, AsRatioOrLength.AsRatio, 1);
// tangent.StartCoordinate = (0.5, 0.0)
// tangent.EndCoordinate = (1.5, 0.0)

tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtension.NoExtension, 1.5, AsRatioOrLength.AsLength, 1);
// tangent.StartCoordinate = (1.0, 0.0)
// tangent.EndCoordinate = (2.0, 0.0)

tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtension.ExtendTangentAtTo, 1.5, AsRatioOrLength.AsLength, 1);
// tangent.StartCoordinate = (1.5, 0.0)
// tangent.EndCoordinate = (2.5, 0.0)

tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtension.ExtendTangentAtFrom, -1.5, AsRatioOrLength.AsLength, 1);
// tangent.StartCoordinate = (-1.5, 0.0)
// tangent.EndCoordinate = (-0.5, 0.0)

tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtension.ExtendTangentAtFrom, -0.5, AsRatioOrLength.AsRatio, 1);
// tangent.StartCoordinate = (-0.5, 0.0)
// tangent.EndCoordinate = (0.5, 0.0)

Requirements

Target Platforms: Windows 10, Windows 8.1

Reference

IGeometryEngine Interface
IGeometryEngine Members
Overload List