| Here are steps
that can be followed to draft spirals in MicroStation with data that is
usually available on old plans. Refer to Spiral Curve Data
for definitions of spiral curve terminology. It should be noted that,
depending on the accuracy of the plan data, this method may not work as
expected.
Given:
Δ (delta angle)
Dc (Ds)
Ts
Ls
Lc
 Extend
a straight line from the TS point in the same direction as the tangent
line a distance of Ts.- Make a copy of this line and rotate it by 180°-Δ. This will give you the tangents for the entire spiral & curve
combination.
- Use the Place Spiral tool on the Create
Curves toolbar (shown at right) to draft the first spiral section. If
this toolbar isn't displayed, it can be found under Tools > B-spline
Curves > Create Curves
 Type
= Clothoid
initial degree = 0 (tangent)
final degree = Dc (Ds)
Length = Ls
- You will be prompted for the start point, select the
TS location. Next click at the opposite end of the tangent line. The third
point can be an approximate location of the end of the spiral. It defines
the direction of the curve.
- Repeat step 4 for the spiral at the other end of the
curve.
- Use the Place Arc tool with the Edge
method to draft the circular portion of the curve. Specify the curve
length (Lc) and start/end points of the curve. If you receive an
"invalid element" message, it may be due to rounding of the Lc
value when it was computed for the old plans. You may have to adjust this
value to get the curve to plot.
|
