I’m trying to fit two arcs between existing elements. The first element is a clockwise arc R=350m, the last element is a straight line. From this line I start a counter clockwise arc R=800m using “simple arc from element”. Then when I try to close the alignment using “arc between arcs”, I configure it with a double spiral from the R=350 and a single spiral to the R=800, see image. There is a solution, however the results are not correct. the single spiral that fits between two arcs with the same direction has somehow become a spiral in the opposite direction, as shown in the attached image. It doesn’t matter whether I set it up as a compound or a reverse arc, the result is the same.
When correctly finished the alignment should look like this: CW arc R=350 CW spiral A=120 CCW spiral A=100 CCW arc R=300 CCW spiral A=100 CCW arc R=800 straight
When I’m trying to build the alignment in the other direction, with the R=800 as the back element, there is no acceptable solution apart from some ridiculous loops.
I’m using ORD 10.6.0.38, but I get the same result using ORD 10.7.3.18. Does anybody know if I’m doing something wrong?
HI Jan
I tried something similar, ie same type of geometry and to me it looked OK.
I'll try coding precisely the same data combination as you, see if I get the same problems. Any chance you can share your DGN once you have completed your design please ?
Simon Pegg
Bentley Civil Support
Hi Simon,
It might be a very rare occurrence, but to make sure, check the alignment report for the direction of the spiral.I only noticed it because there is a change in curvature.I recreated .the alignment in a separate file, see attachment.
Jan
arc between arcs error alignment.dgn
I'm curious, though I think it may be a little different from your original question. Is this a spiral segment (entry radius=300 and exit radius=800) or a complete spiral (where the radius at one end is infinite)?
The spiral is created as a spiral between two arcs, entry R=300 exit R=800. It's supposed to be in hte same direction as the two arcs. The weird thing is, it is created with those radii, no straight parts, just in the opposite direction.
It was pretty easy to do in InRoads SS2. The exit spiral of the initial curve had to be part of the same curve set as the curve. Both the initial and final curves had to start longer than the ultimate result - i.e., they could not be trimmed but could be extended.
I had the same issue as you in ORD 10.07.00.56 - the combining spiral was reversed.