Create Alignment from Object with minimum radius not respected

[pdufourUPCTG]

Hi all,

I'm trying to create a simple alignment from a polyline with minimum curves radius of 100m - it's an access road for transportation of Wind Turbine Vestas V162, so the smoother curve is the better (see dwg attached).

The problem is Civil3D doesn't respect at all my minimum Radius of 100m - I get everything from 15 to 54, etc.

I try to modify and use a Design Criteria Fille (see Design File attached) with only one speed and radius (25 km/h and 100m) - doesn't work either.

Thanks you all for your help. very appreciated

[BrianHailey]

I'm not exactly sure what's going on but it's not your drawing. I copied your polyline into a drawing created from our template and I'm getting the same result. I'm still looking into it though.

[MMcCall402 · Accepted solution]

I got the same results.  Not sure what it is.

In the meantime you could get around it by filleting the polyline before turning it into an alignment.  There is an option in the fillet command to fillet the entire polyline with one selection.  (Option P)

[BrianHailey]

It has something to do with the length of the lines. I isolated just the first two line segments and got the same result. If I double the length of each line segment (scale it up by a factor of 2), then it works just fine. I'm still at a loss as to why it's doing this. I thought perhaps it had something to do with the design speed but setting it to 1km/h didn't change anything (and I didn't expect it would). 

I also tested it in Civil 3D 2020 and I got the same results so it isn't an issue with a new version. Anyone should be able to replicate this. Draw a polyline with two segments, each 200 units long and at a right angle to each other. Create an alignment from objects, set the curve radius to 100 units and the resulting alignment will have a curve with a radius of 80 units. If you change the polyline so it has 250 units long segments, then the resultant curve has a radius of 100 units.

[MMcCall402]

And once it reduces the radius it uses that value for the next curve(s) in the alignment until the next time it decides that the curve won't fit and reduces it again. This keeps going until the value degrades to something pretty small.

All I can think of is that its trying to maintain some minimum tangent length between curves.

[MMcCall402]

It seems to want the tangent length, before or after the curve, to be at least 1.5 times the radius of the curve.

[BrianHailey]

@MMcCall402 - I was thinking along the same lines but I hadn't really looked into what the numbers would be. Looking at @pdufourUPCTG original polyline, I did notice that once the curves got smaller, they never got larger again so I think you're spot on with that idea.

As far as filleting the polyline prior to creating an alignment out of it, that works for most of it but there are several locations where it can't fillet with a radius of 100m. In those cases, it just doesn't put in a curve at all.

[m_kingdon]

I am not familiar with criteria design so I could be completely wrong, but from reading some of the help files I get the impression that the criteria design is to be used for verification purposes rather than forcing Civil 3D to comply when generating an alignment.

These warning indicators in the table I think are as good as you are going to get.

Addition: I might go as far as saying that the criteria design has no influence whatsoever on how Civil 3D buildings alignments.  It is purely for displaying warnings.  The only factor that influences alignment creation is the radius specified in the Add curves between tangents option, even then Civil 3D seems to take a loose approach and will default to a middle ground radius.  I think the priority is to create an Alignment regardless of if is pass/fails a criteria.