QueryClothoidParameters Method

Queries parameters to be used when creating an instance Polyline or PolylineBuilder class that is a linear approximation to a clothoid. This method must be called on the MCT. Use QueuedTask.Run.

Syntax

C#
Visual Basic (Declaration)

public static void QueryClothoidParameters( 
   MapPoint queryPoint,
   MapPoint startPoint,
   double startTangentDirection,
   double startRadius,
   double endRadius,
   esriArcOrientation orientation,
   esriClothoidCreateMethod createMethod,
   double lengthOrAngle,
   out MapPoint pointOnPath,
   out double radiusOut,
   out double tangentDirectionOut,
   out double lengthOut,
   out double angleOut,
   SpatialReference spatialReference
)

Public Shared Sub QueryClothoidParameters( _
   ByVal queryPoint As MapPoint, _
   ByVal startPoint As MapPoint, _
   ByVal startTangentDirection As Double, _
   ByVal startRadius As Double, _
   ByVal endRadius As Double, _
   ByVal orientation As esriArcOrientation, _
   ByVal createMethod As esriClothoidCreateMethod, _
   ByVal lengthOrAngle As Double, _
   ByRef pointOnPath As MapPoint, _
   ByRef radiusOut As Double, _
   ByRef tangentDirectionOut As Double, _
   ByRef lengthOut As Double, _
   ByRef angleOut As Double, _
   Optional ByVal spatialReference As SpatialReference _
)

Parameters

queryPoint: The query point. The curve paramters are reported for the point on the polyline that is closest to the query point.
startPoint: The start point of the polyline.
startTangentDirection: The tangent direction of the spiral, north azimuth, at the first point of the spiral. The unit of the azimuth is radians.
startRadius: The radius at the start of the spiral. The radius must be greater than zero. Double.Infinity is a valid value for the radius.
endRadius: The radius at the end of the spiral. The radius must be greater than zero. Double.Infinity is a valid value for the radius.
orientation: The orientation of the spiral.
createMethod: The method of creation. esriClothoidCreateMethod.ByLength signifies that lengthOrAngle specifies the length of the entire spiral. esriClothoidCreateMethod.ByAngle signifies that lengthOrAngle specifies the angle, in radians, measuring the span of the arc from the start to the end of the clothoid path.
lengthOrAngle: Either the length of the clothoid or the central angle of the clothoid as specified by createMethod.
pointOnPath: The returned point on the clothoid.
radiusOut: The end radius of the spiral at pointOnPath.
tangentDirectionOut: The tangent direction of the spiral, north azimuth, at the end point of the spiral. The unit of the azimuth is radians.
lengthOut: The length of the spiral.
angleOut: The end angle of the spiral.
spatialReference: (Optional) The spatial reference of the polyline. The default value is null.

Remarks

A clothoid, also known as an Euler spiral, is a curve such that its curvature is equal to a constant times its length. Curvature is a value that measures how curved or flat the curve is at a point. The larger the curvature, the more flat the curve is. The curvature is equal to the reciprocal of the radius. If the radius is infinity, then the curvature is zero. i.e. flat.

Shown below is a clothoid with startTangentDirection = 0, startRadius = double.PositiveInfinity, endRadius = 1, orientation = esriArcOrientation.esriArcCounterClockwise, createMethod = esriClothoidCreateMethod.ByLength, and lengthOrAngle = 10.

Here is a clothoid with startTangentDirection = Math.PI / 4, startRadius = double.PositiveInfinity, endRadius = 0.8, orientation = esriArcOrientation.esriArcClockwise, createMethod = esriClothoidCreateMethod.ByLength, and lengthOrAngle = 10.

Now here is a clothoid such that the start radius is smaller than the end radius. It has startTangentDirection = Math.PI / 3, startRadius = 2, endRadius = 10, orientation = esriArcOrientation.esriArcClockwise, createMethod = esriClothoidCreateMethod.ByLength, and lengthOrAngle = 20.

Example

MapPoint startPoint = MapPointBuilder.CreateMapPoint(0, 0);
double tangentDirection = Math.PI / 6;
esriArcOrientation orientation = esriArcOrientation.esriArcCounterClockwise;
double startRadius = double.PositiveInfinity;
double endRadius = 0.2;
esriClothoidCreateMethod createMethod = esriClothoidCreateMethod.ByAngle;
double angle = Math.PI / 2;
esriCurveDensifyMethod densifyMethod = esriCurveDensifyMethod.ByLength;
double densifyParameter = 0.1;

Polyline polyline = PolylineBuilder.CreatePolyline(startPoint, tangentDirection, startRadius, endRadius, orientation, createMethod, angle, densifyMethod, densifyParameter, SpatialReferences.WGS84);

int numPoints = polyline.PointCount;
MapPoint queryPoint = polyline.Points[numPoints - 2];

MapPoint pointOnPath;
double radiusCalculated, tangentDirectionCalculated, lengthCalculated, angleCalculated;

PolylineBuilder.QueryClothoidParameters(queryPoint, startPoint, tangentDirection, startRadius, endRadius, orientation, createMethod, angle, out pointOnPath, out radiusCalculated, out tangentDirectionCalculated, out lengthCalculated, out angleCalculated, SpatialReferences.WGS84);

MapPoint startPoint = MapPointBuilder.CreateMapPoint(0, 0);
MapPoint queryPoint = MapPointBuilder.CreateMapPoint(3.8, 1);
double tangentDirection = 0;
esriArcOrientation orientation = esriArcOrientation.esriArcCounterClockwise;
double startRadius = double.PositiveInfinity;
double endRadius = 1;
esriClothoidCreateMethod createMethod = esriClothoidCreateMethod.ByLength;
double curveLength = 10;
MapPoint pointOnPath;
double radiusCalculated, tangentDirectionCalculated, lengthCalculated, angleCalculated;

PolylineBuilder.QueryClothoidParameters(queryPoint, startPoint, tangentDirection, startRadius, endRadius, orientation, createMethod, curveLength, out pointOnPath, out radiusCalculated, out tangentDirectionCalculated, out lengthCalculated, out angleCalculated, SpatialReferences.WGS84);

// pointOnPath = (3.7652656620171379, 1.0332006103128575)
// radiusCalculated = 2.4876382887687227
// tangentDirectionCalculated = 0.80797056423543978
// lengthCalculated = 4.0198770235802987
// angleCalculated = 0.80797056423544011

queryPoint = MapPointBuilder.CreateMapPoint(1.85, 2.6);

PolylineBuilder.QueryClothoidParameters(queryPoint, startPoint, tangentDirection, startRadius, endRadius, orientation, createMethod, curveLength, out pointOnPath, out radiusCalculated, out tangentDirectionCalculated, out lengthCalculated, out angleCalculated, SpatialReferences.WGS84);

// pointOnPath = (1.8409964973501549, 2.6115979967308132)
// radiusCalculated = 1
// tangentDirectionCalculated = -1.2831853071795867
// lengthCalculated = 10
// angleCalculated = 5

tangentDirection = Math.PI / 4;
orientation = esriArcOrientation.esriArcClockwise;
startRadius = double.PositiveInfinity;
endRadius = 0.8;
createMethod = esriClothoidCreateMethod.ByLength;
curveLength = 10;

Polyline polyline = PolylineBuilder.CreatePolyline(startPoint, tangentDirection, startRadius, endRadius, orientation, createMethod, curveLength, esriCurveDensifyMethod.ByLength, 0.5, SpatialReferences.WGS84);

Requirements

Target Platforms: Windows 10, Windows 8.1

Reference

PolylineBuilder Class
PolylineBuilder Members