Microscopic radii on alignments

[jncslc]

We're working on an alignment that represents a fiber optic line covering many miles. We created the alignment using a pline of multiple vertices. All vertices were set to 0 radius since we unchecked the box "add curves between tangents" and since curves aren't critical for our design. We also didn't add curves because we didn't want those curves to affect our overall length.

 

We then added many Station Offset alignment labels to report the station/offset for many COGO's that were placed along the alignment (a few feet left/right of the alignment). On a few labels they reported a station/offset that was incorrect. We found that these labels sat in what I'm calling an "undefined" area (see my sketch). The labels could not project a perpendicular line to the alignment OR the line they could project was very far away.

 

I determined that maybe curves were required at each vertex to properly define those "problem" labels. So I recreated the alignment and specified curves of 0.001' at each vertex. This created some strange anomalies especially where the angle of some vertices were near 180. It fixed the problem on some, not on others. But I didn't want to use this alignment fearing other undiscovered issues.

 

My question is, can Civil 3D handle microscopic vertices? If so what am I doing wrong or what would be a good workaround.... other than manually adjusting those problem vertices with the geometry editor as I find them?

alignment issue.pdf

[Bill_Myron]

I think you may have found an issue that really doesn't matter and over thinking it.

 

I cant think of a reason to put an offset or a reference to an offset in that area.

 

If you really want to put something there, I would simply create an offset alignment on either side. Place your COGO points along that.

[jncslc]

The alignment vertices and those COGO locations are determined by a field survey that can't be changed just to overcome this limitation of C3D. In the end we need a dwg that shows stationing along that alignment and C3D labels that indicate the station/offset of COGO's around that alignment.

 

Why would C3D alow you to create an alignment with no radii on the vertices and then not function properly when labeling in those undefined areas???

 

I think you may have found an issue that really doesn't matter and over thinking it.

 

I cant think of a reason to put an offset or a reference to an offset in that area.

 

If you really want to put something there, I would simply create an offset alignment on either side. Place your COGO points along that.

[eldon]

Does the fibre optic cable really turn that sharply? What is its minimum radius, 15 times the cable diameter? If you put in a realistic curve radius, it might work.

 

When the survey was carried out, did they survey the IP instead of the true ends of straights? i.e. one field point instead of two.

[jncslc]

It does have a minimum radius but they survey just once at each PI since the cable is buried and accuracy is lacking.

 

Does the fibre optic cable really turn that sharply? What is its minimum radius, 15 times the cable diameter? If you put in a realistic curve radius, it might work.

 

When the survey was carried out, did they survey the IP instead of the true ends of straights? i.e. one field point instead of two.

[eldon]

....We also didn't add curves because we didn't want those curves to affect our overall length.....

 

Have you checked what the length is with and without curves? My suspicion is that it would not make a great deal of difference. Adding curves would be more realistic and make the labels work correctly.

[Bill_Myron]

That "undefined area" is not a limited capability of Civil 3D. It is a real world limited capability. Without real world curves on the vertices, there is no way to come up with an offset in that area, unless it references a piece of your alignment that you don't want. It just doesn't exist in the way that you want it to.

 

In my opinion, those COGO points that are in that area are useless for any kind of survey or layout or design.

[jncslc]

I see your point Bill. A curve of some radius will have to be used. It seems that my 24+ mile alignment is shorted by maybe a foot when using a radius between 0.1' and 0.01', which makes my line more manageable. Hopefully our future alignments will be this forgiving. We sometimes have many vertices and sharp angles when weaving thru populated areas that could severely shorten our line. Our tolerance level for error is 2' or less.

 

Thanks for the help!

 

That "undefined area" is not a limited capability of Civil 3D. It is a real world limited capability. Without real world curves on the vertices, there is no way to come up with an offset in that area, unless it references a piece of your alignment that you don't want. It just doesn't exist in the way that you want it to.

 

In my opinion, those COGO points that are in that area are useless for any kind of survey or layout or design.