SAC and incorrectly formed TIN

[Buzz0m]

Hi,

I got some great help from here earlier and now I'm back with another question!

I'm modelling a tunnel network and I'm having problems getting the TINs to form in the way I intend them to do! I'm attaching a dwg that visualizes my problem! I've highlighted the problematic traingles (TIN exploded to 3d-face-objects) and drawn 3d polylines where i wish the surface would form.

Here's how the model was built:

1. I made a subassembly with SAC that has curved features (3 arches, two small ones and one big) that form the roof of the tunnel and straight features that form the base and walls of the tunnel
2. I made a corridor along the alignment with the appropriate regions. The area where the problematic triangles are is not a region! The tunnel cross section is supposed to gradualy change from one specific cross section (assembly) to another.
3. I created a TIN-surface based on the links of the assembly. The assemblies consist of two types of link codes: one for the bottom, and another for the roof and walls (ie. the roof and walls are one surface [this could be done by making the walls slightly inwards leaning

There's also a problem with the TIN-network at certain stations were the cross section changes. Is there an easy workaround? The regions endstations are ca. 50cm apart. These triangles are also red...

If you have any hints or tips on how I could get rid of these pesky triangles I would greatly appreciate it!

 - Frans

[sboon]

Your problem is related to the way the triangulation algorithm works.  The rule is that points are always connected to their nearenst neighbours, if possible.  In this case the distance I marked in yellow is less than your red lines, so that is how the TIN lines are connected.

The way around this is to use breaklines.  Adding the red featurelines to your TIN as breaks should fix the problem.

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

[Buzz0m]

Thanks for the pointers!

So much I've figured out, but what about the point codes, the link codes and featurelines I can create from the assembly based on the codes?! Isn't there some kind of functionality that I could use that would save me from the hassle! I'm hoping that this assmebly could be used in all our tunnel projects and I believe Civil has so many hidden options and what not that being forced to add the breaklines "manually" can't be the only way of doing this!

What about the other red triangles I marked? Why aren't they formed consistantly across the whole assembly at that station? What I'm trying to say is that one side is modelled perfectly, but the other has the odd red triangles...

Sorry for being so demanding, but I "need" to solve this! My mental health is depending on it

[sboon · Accepted solution]

Who said anything about adding breaklines "manually"?

Assuming that your subassembly has codes assigned to the points across the top of your tunnel then you can turn on the featurelines which connect those points in the corridor.  You are already using links in the corridor surface definition - just add the new featurelines and see what happens.

For the red triangles - put the drawing in 2D wireframe, plan view and take another look at that area.  Notice how the spacing and offset of the triangles changes from one region to the next, and remember what I said earlier about points always connecting to nearest neighbours.

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

[Buzz0m]

aaah okey I see what you ment! What you said in your first post about the TIN (the delaunay triangulation...) algorithm is of course the explanation in this case also! However I'm forced to find some sort of way to get the triangles formed right without compromising on the assembly accuracy! Is there a reason the surface isn't generated so, that the TIN is created one segment at a time, for instance so that all the assemblies "drawn" in the corridor are connected in order so that it is _not_ possible for the surface to form outside the assembly, kind of like bypassing the cross sections that were generated in the corridor?! Can this be done somehow? What I'm looking for is something like the "loft" function in 3d modeling!

The problem with the breaklines is that the "curved" surface is generated with SAC as an arc instead of multiple points connected by lines (I believe this is called tesselation?). This means  - if I'm correct - I only can add a link code to the problematic tunnel roof surface and point codes to the ends of the arc...?! And all the red breaklines I drew cant be added based on point codes! At least not with the assembly I used! Was this what you were suggesting I should try? I was assuming that you ment I should draw the breaklines and add them in what I cald a "manual" way! Sry for not explaining myself better 😃

[nilesh33 · Accepted solution]

Hi,

I am also modeling Tunnel (with almost same cross section) in civil 3d using SAC subassemblies. I have same problem in my model.

Your problem is at widening of tunnel or layby.

May be you have used 3-point arc in your roof subassembly. That's why gradual increase is not possible in surface.

You need to create tessellation points for that 'small arc' in your subassembly. That is what solved same problem in my model.

If you can post SAC subassembly, I can help you out with this.

Refer this post may help you.

Post

[Buzz0m]

Thanks to nilesh33! When I told my collegue about the "swap edge" command (it was mentioned in the link to one of your original posts) he laughed at me and said "hah lol noob"... 😄 Obviously that's one of the basic tools of which I have never heard of! It solved my problem and keeps the triangulation correct even after rebouilding the surface and corridor!

This seems to be a bit of work too if one has to do alot of this sort of tweaking, but I'm satisfied with this solution...

How does the three-point arc affect the triangulation? The subassembly is a bit messy and hard to get a grip on without somebody explaining (at least I think so...). I can't post the subassembly, because the format isn't supported... posting the subassembly in a .dwg file isn't going to help either, is it?

 - Frans

[Buzz0m]

After working a while with my subassemblies: Sboon's solution is the best. The edit surface -tools are imho not good, in the sense that they tend to mess the surface up and are hard to keep track of. Using pointcodes is necessary when one want's a good result...

Using Archs in the subassembly is also a bit tricky. If there is a slight turn in the alignment the triangles tend to form incorrectly. I used trigonometric functions to get the arch into segments of lines and added point codes to each of the line ends. This was the only way I could get the surface to form correctly and keep forming correctly even after updates.

Thanks to Nileesh and Sboon for the help!