AutoCAD Civil 3D

[#1]

When adding data to a surface, there is the option to add it as a "Non-destructive" breakline. 

http://screencast.com/t/qBnciKzR3i

What is this good for? I created a surface, copied it, and created a volume surface between the two of them. As expected, the resultant volume was 0.

I then draw a 3d polyline and snapped to elevations on the surface. I then took that 3d polyline and moved it up 5'. I then added that breakline to the surface as a "Non-destructive" breakline and the resultant volume between the original surface and the one modified with the new breakline was still 0. Absolutely no change was made to the actual surface, it just added additional triangles. 

Anyone have any idea why anyone would ever use such a thing? I'm trying to find a reason it's even option and I'm coming up blank. There has to be SOME reason it's there.

[#2]

I have never found a good reason to use non-destructive breaklines. However, when defining surface hide boundaries, I will use non-destructive often. This "trims" the TIN lines (by adding new verticies) instead of removing them. Essentially, when you use them for breaklines, you get new vertices when your breakline crosses a TIN line. Again, I"ve found no good use for them as breaklines.

[#3]

I've used them rarely, but there have been a few times when I needed to preserve the existing TIN either inside or outside of a closed area before adding new data to the surface.  A non-destructive breakline is useful for that purpose.

[#4]

I suspect that the "non destructive" part (as sboon suggested) does what it says - it merely preserves the original TIN structure but with additrional TIN lines at where the non destructive breakline crosses the TIN.

From the help "....The elevation for each new point is extracted from the original surface triangle, therefore maintaining the integrity of the original surface..." so the line could have been raised 100 feet and it still wouldn't have affected the TIN

I also use them in the same way as mathewk and sboon do as I guess this is the intended use.

[#5]

I would define a "non-destructive Breakline" as a "projected contour" added to the surface definition.

It does NOT affect the curvature of the C3D surface, just adding triangles to it. 

[#6]

So what is the purpose of these things? In the context of breaklines (not boundaries) I can't see any use for them either. A breakline that doesn't influence the surface isn't really a breakline in my thinking.

[#7]

Neil, I think Steve got it.  You can use it to create a breakline on the existing surface before you perform edits on one side of it.  If you paste a surface onto a larger one, for example, C3D will triangulate from the edge of the surface you paste in, to the nearest data on the larger surface.  If you were to add a non-destructive breakline first you can control where that match point will be.

I had never looked at these, never used them.  But I have used feature lines to do something similar: draw feature line, elevations from surface (add verticies), add feature line back into surface to make sure that it doesn't change at this point, while I edit nearby.  Non-destructive breaklines look like a better way to go for that.

This is why I love coming here: always new ideas floating around.  (New to me anyway.)

[#8]

Ok I get it now. I assumed it ALWAYS maintained the triangulation of the TIN, but after running some tests I see that it's position in the surface definition is a factor. Good to know.

[#9]

That sounds about right. I think I've seen post that describe exactly what you're talking about. Thanks for figuring it out.

Allen