ArcGIS Pro 3.0 API Reference Guide
ArcGIS.Core.Geometry Namespace / IGeometryEngine Interface / QueryTangent Method / QueryTangent(Segment,SegmentExtensionType,Double,AsRatioOrLength,Double) Method
The segment to which the tangent line is constructed.
Specifies the extension method that determines the direction and position of the tangent line.
Specifies the distance along the segment from which the tangent line is constructed.
Determines whether the distanceAlongCurve is returned as a ratio of the segment length or as length from the start point.
Specifies the length of the returned tangent line.
Example

In This Topic
    QueryTangent(Segment,SegmentExtensionType,Double,AsRatioOrLength,Double) Method
    In This Topic
    Constructs a line tangent to a segment from a point at a specified distance along the segment.
    Syntax

    Parameters

    segment
    The segment to which the tangent line is constructed.
    extensionType
    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
    ExceptionDescription
    segmentis null or empty.
    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 extensionType 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 extensionType 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 extensionType = SegmentExtensionType.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 extensionType = SegmentExtensionType.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

    SegmentExtensionType.ExtendEmbeddedAtTo, SegmentExtensionType.ExtendEmbeddedAtFrom, and SegmentExtensionType.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 extensionType = SegmentExtensionType.ExtendEmbeddedAtTo.

    QueryTangent_EmbeddedAtToPositive

    If the input segment is not an elliptic arc segment, then SegmentExtensionType.ExtendEmbeddedAtTo, SegmentExtensionType.ExtendEmbeddedAtFrom, and SegmentExtensionType.ExtendEmbedded are equivalent to SegmentExtensionType.ExtendTangentAtTo, SegmentExtensionType.ExtendTangentAtFrom, and SegmentExtensionType.ExtendTangent respectively. There are cases when the tangent cannot be extended as specified by the extensionType parameter. For example, if the distanceAlongCurve is negative and extensionType = SegmentExtensionType.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 extensionType = SegmentExtensionType.ExtendTangentAtFrom, then the tangent line is constructed at the end point of the input segment.

    Example
    QueryTangent
    LineSegment line = LineBuilderEx.CreateLineSegment(new Coordinate2D(0, 0), new Coordinate2D(1, 0));
    
    // No extension, distanceAlongCurve = 0.5
    LineSegment tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtensionType.NoExtension, 0.5, AsRatioOrLength.AsRatio, 1);
    // tangent.StartCoordinate = (0.5, 0.0)
    // tangent.EndCoordinate = (1.5, 0.0)
    
    tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtensionType.NoExtension, 1.5, AsRatioOrLength.AsLength, 1);
    // tangent.StartCoordinate = (1.0, 0.0)
    // tangent.EndCoordinate = (2.0, 0.0)
    
    tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtensionType.ExtendTangentAtTo, 1.5, AsRatioOrLength.AsLength, 1);
    // tangent.StartCoordinate = (1.5, 0.0)
    // tangent.EndCoordinate = (2.5, 0.0)
    
    tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtensionType.ExtendTangentAtFrom, -1.5, AsRatioOrLength.AsLength, 1);
    // tangent.StartCoordinate = (-1.5, 0.0)
    // tangent.EndCoordinate = (-0.5, 0.0)
    
    tangent = GeometryEngine.Instance.QueryTangent(line, SegmentExtensionType.ExtendTangentAtFrom, -0.5, AsRatioOrLength.AsRatio, 1);
    // tangent.StartCoordinate = (-0.5, 0.0)
    // tangent.EndCoordinate = (0.5, 0.0)
    Requirements

    Target Platforms: Windows 11, Windows 10, Windows 8.1

    See Also