Create spiral curves

In the Create Features pane, line feature construction tools include Spiral Curve construction methods for creating spiral curves as densified polylines. The dialog box is available on the construction toolbar and context menu when you create a feature.

A spiral curve is a curve with a fixed start point and a radius that changes proportionately to its distance on the arc from the start point as it increases or decreases. The geometry is defined with start bearing, a start radius, an end radius, and an arc length or a delta angle.

Spiral curves are commonly used in roadway and railroad design to transition moving vehicles safely into or out of a circular path or a straight line.

Note:

When Ground to Grid is turned on, the direction values you enter are rotated and the radius and arc length values are scaled for the resulting geometry.

To learn more, see Turn ground to grid on or off.

1. If the current map does not contain a polyline feature layer, add it.
   1. On the View tab, click Catalog Pane , and expand Databases .
   2. Expand the default database or the database containing your data.

      To create a polygon feature class, right-click the database, click New and click Feature Class.

   3. Drag the feature class onto the map.

      A feature template with default settings is autogenerated for the new layer.

2. If you are creating line features that require your input values to be stored with the feature in COGO attribute fields, COGO-enable your line features.

   COGO-enabled line feature classes draw with COGO symbology and include a label expression that labels each line with its COGO dimension, when it exists.

   To learn more, see Enable COGO.

3. If you are working with z-enabled features, on the Edit tab, in the Elevation group, choose how z-values are added to your features.

   For steps to add z-values when creating z-enabled features, see Specify an elevation for 3D features.

4. On the Edit tab, set your snapping preferences and open the Create Features pane.
   1. In the Snapping group, enable your snapping preferences.

      Tip:

      To temporarily turn snapping off as you draw a feature, press and hold the spacebar.

   2. In the Features group, click Create .
5. In the pane, choose a line feature template and configure the construction tool.
   1. Click a line feature template, and click the Active template button .
   2. Click Two-Point Line .
   3. Check Continue Two-Point Lines to create connecting two-point line features.

      Creating two-point continuous line features creates a spiral as a feature and updates COGO attributes. If you do not use the two-point line construction tool, the spiral is created as segments and COGO attributes are not updated.

      Continuous two-point line features automatically create the first vertex at the coordinates of the last vertex of the previous two-point line feature.

   The construction toolbar appears at the bottom of the map.

   

6. Click the map or the endpoint of an existing line or arc at which you want to start the spiral curve.
7. Right-click and click Spiral Curve.

   The preview rotates to the calculated tangent direction, and the dialog box appears.

8. Specify the start bearing as a Tangent Direction or a Chord Direction.
9. Specify the Start Radius using one of the following methods:
   • If you are starting from a circular arc tangency, specify the radius value.
   • If you are starting from a straight-line tangency, press Delete to delete the radius value and set the parameter to INFINITY.
10. Specify the End Radius using one of the following methods:
    • If you are ending on a circular arc tangency, specify the radius value.
    • If you are ending on a straight-line tangency, press Delete to delete the radius value and set the parameter to INFINITY.

    Note:

    Specifying equal start and end radii creates a circular arc that is not densified.

11. Specify the length of the spiral as an Arc Length or a Delta Angle.
12. To flip the orientation of the arc preview and the resulting sketch, click Left or Right.
13. Click the Densify by drop-down arrow and specify how you want to densify the spiral.
    • Deviation—Creates segments with varying lengths that deviate from a true curve within the maximum specified distance.
    • Angle—Creates segments that do not exceed the specified angle. Line segments decrease in length as the curvature increases.
    • Length—Creates segments that do not exceed the specified length.
14. Press Enter to close the dialog box and create the spiral curve.