Curves Menu

8.14  Spiral Curve  (SR)

FUNCTION:  The Spiral Curve routine is used to compute points (stations) along a spiral curve set from the PI of the spiral's tangents.

Activate the Spiral Curve routine by picking from the Curves menu; by pressing [Alt][V], [S], or by typing command SR at any data entry prompt.

P.I. Point:  This is the currently occupied point, which is also the PI of the spiral's tangents.  If you have an occupied point this box will automatically be filled for you.  Changing the From Point is equivalent to running the Go To routine (GT - Section 6.06), and will change the BS Bearing.  To select a new backsight bearing use either the Enter Backsight Bearing routine (EB - Section 6.08) or the Enter Backsight Point routine (EP - Section 6.07).

TIP: Left-click the [Pts] button to select a point from the Point Manager (see Section 6.09).  Right-click the [Pts] button to select a point from the CAD window (see Picking Points in CAD in Section 2.03).

Spiral Len:  Enter the length of the spiral and press [Enter] or [Tab].

R/A/C:  Click [q] and choose the central curve parameter known: Radius; (degree of curve) Arc; or (degree of curve) Chord.

Value:  Enter the value for the central curve parameter selected in the previous prompt and press [Enter] or [Tab].

PT / TS:  Click [q] and choose the point of known station.

Station:  Enter the station of the point chosen in the previous prompt and press [Enter] or [Tab].

Spiral Int:   Enter the interval between stations to be computed along the spiral and press [Enter] or [Tab].

Curve Int:  Enter the interval between stations to be computed along the central curve and press [Enter] or [Tab].

Angle @ PI:  Enter the angle  and press [Enter] or [Tab].

Direction:  Enter the direction of the curve relative to the forward direction of travel by typing L (for curving to the left) or R (for curving to the right) and press [Enter][Enter], or [Tab][Enter], or click [Go].

"Sight" Survey responds to your data entry by first printing into the Text Output window a table of stations, deflections and offsets for all the computed points; then establishes coordinates for all computed points by using an automated Side Shot routine.  If your drawing functions are active, the Side Shot routine also plots your points.  You may then use the Inverse routine to connect the points with linework.

TIP: To draw parallel spirals use the Traverse Right of Way routine (RW - Section 7.13).  Make sure you set your Spiral Interval to a lower value so you can produce enough points to approximate the offset spiral.