Create Combined CurveCreate Combined Curve type Arc, Spiral, Arc

(This functionality is available with the Computations module)
(Not available in LISCAD Lite)

Creates a new compound combined curve consisting of an arc, a partial spiral and another arc, by specifying tangent lines, tangent distances and radii.

To run this option, select Create/Combined Curve and Method/Arc, Spiral, Arc from the Computations task to display the relevant dialog box.

Before using this command, check the Configure/Alignment command and ensure you have the required design constants set. The method is not available unless Cubic Parabola is selected in that dialog.

The combined curve to be created will be given the attributes currently defined via the Attributes/Line command, and the associated points created will be given the attributes currently defined via the Attributes/Point command. You should use these commands to set the required attributes before creating any combined curves.

Important: Refer to the Creation Methods-Special Notes topic and ensure that you are familiar with its contents.

Create Combined Curve

Item Used to
Type Display the type of combined curve to be created.
  • Arc In, Spiral, Arc Out
Technique Display the technique available.
  • Ends and Centres
Point ID Key in the point identifier to be assigned to the first new point created in the process. Other new points will get the next available identifier.
Interpolate Elevations Select this option to interpolate elevations at the newly created tangent points.
Parameters Enter or specify the values of the parameters required to compute the combined curve.

Depending upon the technique selected some of the following edit fields will be enabled and others will be disabled. The fields that are enabled are the required input parameters for the technique selected. The disabled fields will be filled out when the combined curve is computed.
  • Start Arc Point: The start point of the large radius incoming arc.
  • Large Centre Point: The centre of the large radius incoming arc.
  • End Arc Point: The end point of the small radius outgoing arc.
  • Small Centre Point: The centre of the small radius outgoing arc.
  • Arc In: The arc length of the incoming large radius arc.
  • Spiral: The compound spiral length between the arcs.
  • Arc Out: The arc length of the outgoing small radius arc.
Compute Compute the combined curve and display it on the screen. All the relevant combined curve parameters (spiral lengths etc.) will be displayed in the dialog.
If any unusual circumstance occurs in the creation of the combined curve, a warning is also displayed on the dialog indicating the problem. For example, if the curve does not fit, 'Warning - Curve beyond Reference Points' is displayed.
Accept Save the computed combined curve to the database.
Note that if the tangent lines were part of an alignment, the alignment is automatically modified to be along the new combined curve.
Next Find the next available Point ID in the data base.  This field is active when the Point ID edit field has the focus.
Last Find the last available Point ID in the data base.  This field is active when the Point ID edit field has the focus.