Parabola

[rihiz]

I needed to get a parabola.. Didnt know how to do it.. typed in parabola, and found that it worked! Selected 3 points and it drew me one that fits perfectly, but it still has the three points and slashed line. How do I make it the line I want ( layer ) and make the rest disappear? I cant find how to do either.

[Cad64]

I have moved your question to the Civil 3D section since standard Autocad does not have the Parabola command.

 

Take a look at this link for information on creating Parabolas in Civil 3D: https://knowledge.autodesk.com/support/autocad-civil-3d/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/Civil3D-UserGuide/files/GUID-510C7108-4947-414A-9EC9-9E587F6A31C3-htm.html

[BIGAL]

Not sure about question points disappear once you tick the green arrow Civ3d creates 3 Aecc cogo points there is no doubt a parabola "style" as well. The only thing is parabola can have multiple formulas

[lrm]

Let's assume that the axis of symmetry of the parabola is vertical (parallel to the y axis) and that you know where the slope is zero (parallel to the x axis, point A in the drawing). You can then create an exact parabola using 3 CV (Control Vertex) points as follows.

 

Determine points C and D where C is the midpoint of AB and D is at the intersection of a vertical line through C and a horizontal line through A.

 

Draw a spline using the CV method and points A, D, and B.

 

 

Since only 3 CV's are used the resulting spline will be degree 2 (not 3) and will be an exact parabola.

 

Command: [b]SPLINE[/b]
Current settings: Method=CV   Degree=3
Specify first point or [Method/Degree/Object]: [b]m[/b]
Enter spline creation method [Fit/CV] <Fit>: [b]cv[/b]
Current settings: Method=CV   Degree=3
Specify first point or [Method/Degree/Object]:
Enter next point:
Enter next point or [undo]:
Enter next point or [Close/Undo]:

[MACC]

On 10/23/2017 at 11:27 AM, lrm said:

Let's assume that the axis of symmetry of the parabola is vertical (parallel to the y axis) and that you know where the slope is zero (parallel to the x axis, point A in the drawing). You can then create an exact parabola using 3 CV (Control Vertex) points as follows.

 

Determine points C and D where C is the midpoint of AB and D is at the intersection of a vertical line through C and a horizontal line through A.

 

Draw a spline using the CV method and points A, D, and B.

 

 

Since only 3 CV's are used the resulting spline will be degree 2 (not 3) and will be an exact parabola.

 

 

Command: [b]SPLINE[/b]
Current settings: Method=CV   Degree=3
Specify first point or [Method/Degree/Object]: [b]m[/b]
Enter spline creation method [Fit/CV] <Fit>: [b]cv[/b]
Current settings: Method=CV   Degree=3
Specify first point or [Method/Degree/Object]:
Enter next point:
Enter next point or [undo]:
Enter next point or [Close/Undo]:

 

 

Many thanks. So far it works excellent. I have noticed that the Point D is always the PVI of the curve if you working with vertical curves that is.

[BIGAL]

You can duplicate a Road Vertical curve given G1 G2 and length, the formula is readably out there and can be converted to lisp.