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Valued Mentor
Posts: 265
Registered: ‎09-28-2010

# Reduced Maximum Length for Surface Triangles Causes Surface Holes

663 Views, 12 Replies
10-22-2012 05:44 PM

Has anyone had instances where you set your tolerance for the maximum triangle lenth to say 50m to reduce the amount of triangles along the edge that run at long distances. When I do this I end up with multiple surface holes and I'm not sure why as there are points in the area.

I thought well maybe it's because i should've reduced my max triangles first then added breaklines. Would this matter? I also thought I could add a line to the surface to fix the holes vs. deleting surface lines along the entire edge of a surface for many many miles. Anyone with a trick or two they'd like to share on this one?

*Expert Elite*
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# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

10-22-2012 10:55 PM in reply to: LeafRiders

The sad reality is the maximum triangle length function is not limited to the exterior triangles of a surface. Any triangle that has a side length greater than the maximum is removed no matter where it occurs in the surface. That can result in holes as you are seeing. Your options are to add data in the areas where it leaves holes to reduce the side lengths or increase the max. length setting and add a boundary to handle the undesired edge triangles.

If the algorythm were designed to affect only the edge triangles it would be much more useful.

Neil Wilson (a.k.a. neilw)
Infrastructure Suite/C3D 2013, LDT 2004, Power Civil v8i SS1
WIN 7 64 PRO
HP Pavillion h8xt, i7 2600, 12 GB
http://www.sec-landmgt.com
Valued Contributor
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Registered: ‎05-22-2007

# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

10-25-2012 05:31 PM in reply to: Neilw

Neil,

I have a follow-up question on these TIN triangles. How does autocad determine where the triangles should go? I don't necessarily want to see the algorithm itself, but I often paste barely non-overlapping surfaces together and wish there was a way to make the resulting composite look better... It does NOT seem to try and use close points... sometimes it'll use on point on one side of the gap between the surfaces, and connect that one point to EVERY point on the other surface.. (I may as well just draw all the triangles by hand...)

Any thoughts on how the software figures out where to put the triangles? Is there a way to force it to use small triangles if possible?

Thanks again!

-d

Attached image isn't great.. but you can see all the blue lines (Triangles) in the middle which, instead of going from one point to the other 'across the way', all start from point and form this big fan of skinny, long triangles...

*Expert Elite*
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# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

10-25-2012 07:46 PM in reply to: LeafRiders

because the triangle is 50m or greater? I suggest people use that function with extreme prudence.

Thank you

Joseph D. Bouza, P.E. (one of 'THOSE' People) Civil 3D 2012 & 2013
HP Z210 Workstation
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Note: Its all Resistentialism, so keep calm and carry on

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*Expert Elite*
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# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

What I think is going on in your image is a typical symptom of breaklines with too few elevation points. Imagine modeling a road with centerline and edge breaklines. The centerline breakline has vertices avery 20 feet but the edges only have them every 100 feet. Since the triangles can only connect to the vertices you'll end up with some long triangle edges along the edge of the road. In C3D, when you add a breakline to a surface you will get a dialogue that allows you to add vertices to the breaklines at a specified interval. C3D automatically interpolates elevation points along the breakline in the breakline database which serves to densify the TIN and reduce those long edges.

Now when you paste 2 surfaces together the triangulation has to form across the edges of the 2 surfaces. The edge triangles of those surfaces probably have long sides since boundaries of surfaces typically don't have interpolated vertices. You should be able to improve the merging by adding a boundary as a breakline with densified vertices to each of the 2 surfaces.

Neil Wilson (a.k.a. neilw)
Infrastructure Suite/C3D 2013, LDT 2004, Power Civil v8i SS1
WIN 7 64 PRO
HP Pavillion h8xt, i7 2600, 12 GB
http://www.sec-landmgt.com
Valued Mentor
Posts: 265
Registered: ‎09-28-2010

# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

10-26-2012 08:09 AM in reply to: Neilw

RE: " It does NOT seem to try and use close points... sometimes it'll use on point on one side of the gap between the surfaces, and connect that one point to EVERY point on the other surface.. (I may as well just draw all the triangles by hand...) "

I knew someone else would chime in with like issues. It's extremely painful. I've spent days trying to fix my EG surface in more ways than I can think of. This is exactly what I'm talking about.

Solution:

"In C3D, when you add a breakline to a surface you will get a dialogue that allows you to add vertices to the breaklines at a specified interval. C3D automatically interpolates elevation points along the breakline in the breakline database which serves to densify the TIN and reduce those long edges.

Now when you paste 2 surfaces together the triangulation has to form across the edges of the 2 surfaces. The edge triangles of those surfaces probably have long sides since boundaries of surfaces typically don't have interpolated vertices. You should be able to improve the merging by adding a boundary as a breakline with densified vertices to each of the 2 surfaces."

Thanks for Sharing a valid solution, I will certainly keep this in mind going forward. Thanks neilw

Valued Mentor
Posts: 265
Registered: ‎09-28-2010

# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

10-31-2012 01:53 PM in reply to: LeafRiders

I need more clarification based on your "breakline dialogue box" comment. I set my distance to 5m and Mid-ordinate distance to 1 and I sill get dreadful "surface holes" where my breaklines are longer than the Max triangle length. Please show where the setting is for the setting you describe. Thanks.

One thing I did find is when I have a breakline that goes for a longer distance maybe where there isn't survey I need to create nodes on the polyline to breakdown the eventual breakline further. This is a painful process. Thoughts?

Valued Mentor
Posts: 265
Registered: ‎09-28-2010

# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

10-31-2012 02:40 PM in reply to: LeafRiders

Screenshot attached... Settings are 5m distance, 1m mid-ordinate distance, max triangle length 100. Someone tell my why this is an issue? See attachment

*Expert Elite*
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# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

10-31-2012 02:49 PM in reply to: LeafRiders

First off, your breakline dialogue shows the type as Proximity which is why your Supplementing Factors settings are inactive. You will need to set it to Standard to adjust the settings. You will also need to toggle on the Supplementing Factors option to apply the supplement settings.

Second, you cannot change the supplementing settings on breaklines that have already been added to the surface. You will have to remove them from the surface definition and re-add them with the desired settings.

Third, supplementing the breaklines may not solve your problem if the distance between breaklines is greater than the maximum triangle length. It appears from your screen capture that this might be why the triangles are not forming across the hole.

Neil Wilson (a.k.a. neilw)
Infrastructure Suite/C3D 2013, LDT 2004, Power Civil v8i SS1
WIN 7 64 PRO
HP Pavillion h8xt, i7 2600, 12 GB
http://www.sec-landmgt.com
Valued Mentor
Posts: 265
Registered: ‎09-28-2010

# Re: Reduced Maximum Length for Surface Triangles Causes Surface Holes

10-31-2012 03:06 PM in reply to: Neilw

The parallel distance between any of the breaklines is maximum of a few metres, so that's a non-issue when I'm using 50-100m as a Max triangle length. This is to cut back the outer edge runnign breaklines that create offshoots in ones section views.

As for #2 changing breakline settings after their added to the surface (no kidding), thanks for mentioning it.

As for #1 please be more specific to what you're stating, we've covered a lot of angles here and can't get this to work. So what we have is polylines from survey figures that are flattened and saved as our breaklines. We use these as proximity and the surface properties converts them to "Standard" when selecting proximity ( this is a civil 3d surface setting).

Are you saying that proximity breaklines are unable to have supplementing factors?