Create Spiral-Curve-Spiral

[Anonymous]

Hi,

I am working on road pavement rehabilitation project and the pavement section is located at a curve section. I have attached a rough sketch for more information. I want to change the horizontal alignment with a curve and connect the new alignment to the existing at a point where the existing is straight.

I tried to use spiral-curve-spiral function but I've got an error message "cannot create a free entity, no alignment sub-entities currently exist". I have no idea what this means. 

What I did was, created an alignments using red and blue lines (objects) and selected the red alignment, selected Geometry Editor, selected Add Free Spiral-Curve-Spiral, then selected Free Spiral-Curve-Spiral (between two entities). After that I got this error message.

Can someone explain me how I can do this, please ?

Thank you.

[Pointdump]

N,

Alignments are not my forte, but I can remember spiral-curve combinations being exasperatingly rigid. If you can't create a free S-C-S, then try fixed or floating and change it to free afterwards in the Geometry Editor.

Can you post your drawing?

Dave

[Anonymous]

Yes, I have attached a copy of the drawing. 

What I'm trying to do is re-align the centreline of the floodway with a simple curve (as much as close to the existing centreline) and connect the extended centreline to the existing with a spiral (to maintain the tangent at each connection point). 

If I'm not clear enough yet, please ask me explain further.

Thank you.

[Pointdump]

N,

"I tried to use spiral-curve-spiral function but I've got an error message "cannot create a free entity, no alignment sub-entities currently exist". I have no idea what this means."

A Free Entity is a line, curve, or spiral that is dynamically attached and tangent to (between) two lines or curves that belong to the same alignment.

I'm not able to create an alignment from your drawing. Not only am I not clear on which are the centerlines, they all seem to be 3D Polylines. When I convert them to 2D Polylines I lose the arcs and the 3D Polyline becomes 63 short 2D Polylines.

Workflow:
1. Create new Tangent Lines for the Road Centerline.
2. Create the alignment.
3. Add Free Curves between all the Tangent Lines.
4. Add Free Spirals between each Tangent Line and its ajoining Curve.

You can maintain tangency with just the curves. Do you really need the spirals?

Dave

[Anonymous]

Hi Dave,

Thank you for your try and sorry for not explaining the drawing.

I have attached a new file. As you may see the cyan line is the existing centreline. The green box (lines) shows the existing causeway (concrete pad) over the existing box culvert (7m wide). The road pavement marked in white is concrete causeway (approx. 6m wide). The sections with blue edges are bitumen seal road pavement.

My project is to keep the green colour concrete pad as it is and overlay and widen the rest of the concrete causeway (while lines) to 7m. Then make the sealed section (it is up to the designer to decide how far this work should be extended) match to the concrete causeway. 

Obviously I have to keep my new horizontal alignment as much as close to the existing. So, my intention is to use a simple curve at the middle section and connect the curve to to lines at the two ends with spirals. 

If you could, please let me know how I can do this.

Thank you.

[sboon]

I don't have the 2017 software available right now, but here is my suggested workflow:

• Use the Create Line by Best Fit tool to create the two tangents on either side.  You may have to try it a few times, to get a feel for where the survey data starts to transition into the existing curve.
• Fillet those two lines together, and use them as the basis for your alignment tangents.
• Those two tangent lines will be fixed subentities - which is what you need to create a free SCS subentity.

Alternate method - you can also use the best fit curve tool to approximate the existing curve, add that to the alignment as a fixed 3 point subentity and then use the Free Spiral tool to connect the curve to the tangents.  Note - this method is a little more tricky, as your curve cannot cross either tangent.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

Edit - I was able to XREF your drawing into this file and try it.  As I expected the existing curve doesn't fit the tangents.  I can get close by playing with the spiral lengths but without a design speed or criteria this may not work for you.