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sumanthap
Posts: 7
Registered: ‎05-13-2009
Message 1 of 12 (457 Views)

Surface "Blending" Issues

457 Views, 11 Replies
11-15-2012 11:32 AM

Hi!

 

Some background: We have a composite surface of existing surveyed contours as a TIN pasted into existing aerial contours that we received from a client.  We used polylines to generate our proposed contours, and then generated a proposed surface from that.  We've made a blank surface, pasted in the existing surface, and are trying to paste in our proposed surface...  only the existing contours outside of the proposed suface no longer line up correctly once we do.

We've tried applying the method laid out here: http://forums.autodesk.com/t5/AutoCAD-Civil-3D/Blending-pasted-surfaces/td-p/3063600 (and the link referenced in the bottom) but are still having trouble getting the surface to work.  We've tried offsetting as little as 0.25' and as much as 5' with the feature line draped over the existing surface, but it seemed that the greater the offset, the greater the discrepancy.

 

Just to make sure we even tried that correctly - should the breaklines that we add be standard or non-destructive?  (I've tried it both ways with little success either way, so I don't know if it matters much in this instance, but perhaps for future reference it would help.)

 

I've attached a screen shot of our surfaces.  The pink and green lines are the proposed contours, the white dashed are the existing.  The outer red line is offset 0.25'.  As I've mentioned, we've tried offsetting various amounts with decreasing success.

 

Any suggestions anyone can offer regarding resolving this issue would be greatly appreciated!

 

Thanks!

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troma
Posts: 2,519
Registered: ‎05-21-2008
Message 2 of 12 (450 Views)

Re: Surface "Blending" Issues

11-15-2012 11:48 AM in reply to: sumanthap

Not sure what you're trying to achieve.  You mention two existing surfaces, and one proposed.  Which contours is it you want to line up?  Where and why?

 

It might seem like the why shouldn't matter, but a good understanding of you situation will help someone give you the right advice.


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troma
Posts: 2,519
Registered: ‎05-21-2008
Message 3 of 12 (447 Views)

Re: Surface "Blending" Issues

11-15-2012 11:57 AM in reply to: sumanthap

Couple of points:

 

1. I would use a non-destructive breakline.

 

2. I would consider going more than 5'.  Think maybe 50'.  Remember, the reason there is a jog is because the data doesn't agree.  Someone is wrong, or just inacurate.  I trust a topographic survey 100 times more than contours from aerial photography.

 

3. Delete surface data in the transition zone.  Whether it is 0.25' or 250', this zone must triangulate straight from that non-destructive breakline to the boundary of the surface pasted in.  Turn on surface points in the display, and delete all of them in that zone.  You are erradicating data, to give C3D a chance to make a smooth transition.


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Active Member
sumanthap
Posts: 7
Registered: ‎05-13-2009
Message 4 of 12 (437 Views)

Re: Surface "Blending" Issues

11-15-2012 12:29 PM in reply to: troma

We want to create a true proposed surface.  As it stands right now, the "proposed" surface (Proposed Only and Proposed WIth Transition) we have is created solely from our proposed contours (from polylines) and doesn't incorporate any existing data.  It seems to me that the way to do this would be to make an empty surface (Combined Proposed Surface), paste in the existing surface (xxxxx-EX) to essentially act as a base, and then paste the Proposed Only or Proposed With Transition surface "over" it (by which I mean using edits, with the polyline-based "proposed" surface second in the definition order).  In the area just outside of the red boundary, Combined Proposed Surface (pink and green contours) no longer matches the xxxxx-EX (the white contours), which is the true existing surface.  However, that area is outside the limits of our proposed grading, so it shouldn't change at all.  I get that it's a triangulation issue, but I wasn't entirely sure how to proceed.

 

The proposed surface is important because we want to be able to sample sections from it and run HEC-RAS.  We could manually edit the sections so that the stations/elevations outside of the limits of grading match between existing and proposed conditions, but we'd much rather have the surfaces just line up the way they're supposed to so that they sample similarly in unchanged areas.

 

When we delete the surface points, would that be from the Combined Proposed Surface, or would that be from the Proposed With Transition surface?

 

Thanks,

 

Sumantha

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troma
Posts: 2,519
Registered: ‎05-21-2008
Message 5 of 12 (426 Views)

Re: Surface "Blending" Issues

11-15-2012 12:54 PM in reply to: sumanthap

We want to create a true proposed surface.  I presume you mean proposed for the site, matching existing at the perimeter, and including all the existing surface?

 

As it stands right now, the "proposed" surface (Proposed Only and Proposed WIth Transition) we have is created solely from our proposed contours (from polylines) and doesn't incorporate any existing data.

Why are you designing with contours?  Much easier to design with feature lines, build a surface and generate your contours as part of the TIN surface.

 

 

  It seems to me that the way to do this would be to make an empty surface (Combined Proposed Surface), paste in the existing surface (xxxxx-EX) to essentially act as a base, and then paste the Proposed Only or Proposed With Transition surface "over" it (by which I mean using edits, with the polyline-based "proposed" surface second in the definition order). 

This workflow sounds good to me, but I'm not sure what you mean by Proposed With Transition.  If you define your matchpoint with a non-destructive boundary in the Combined... surface before you paste the Proposed, then C3D will generate the transition by triangulating accross the gap, so to speak.

 

 

In the area just outside of the red boundary, Combined Proposed Surface (pink and green contours) no longer matches the xxxxx-EX (the white contours), which is the true existing surface.  However, that area is outside the limits of our proposed grading, so it shouldn't change at all.  I get that it's a triangulation issue, but I wasn't entirely sure how to proceed.

 

I think it depends on how you have set up the match point.  If you don't want to start over again, try drawing a feature line where you think it should be matching.  Do 'Elevations from surface', pick the EG and add verticies.  Then add the feature line as a standard breakline to the Combined surface.

 

The proposed surface is important because we want to be able to sample sections from it and run HEC-RAS.  We could manually edit the sections so that the stations/elevations outside of the limits of grading match between existing and proposed conditions, but we'd much rather have the surfaces just line up the way they're supposed to so that they sample similarly in unchagned areas.

I agree.

 

When we delete the surface points, would that be from the Combined Proposed Surface, or would that be from the Proposed With Transition surface?

 As said, don't think you need a Proposed With Transition.  Just edit the Combined surface.


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Active Member
sumanthap
Posts: 7
Registered: ‎05-13-2009
Message 6 of 12 (413 Views)

Re: Surface "Blending" Issues

11-15-2012 01:58 PM in reply to: troma

I presume you mean proposed for the site, matching existing at the perimeter, and including all the existing surface?

Yes, sorry if I haven't been making that clear.

 

Why are you designing with contours?  Much easier to design with feature lines, build a surface and generate your contours as part of the TIN surface.

In all honesty? I have tons of experience in plain vanilla AutoCAD, but am relatively new to Civil 3D...  so some old/bad habits are hard to break.  I started to learn 4 years ago, but we've basically been designing for a client that predominantly uses Microstation/InRoads for the past 3 years, so my work with C3D has been pretty spotty.  I'm more or less learning (and/or relearning) as I go (which I know can be dangerous).

 

This workflow sounds good to me, but I'm not sure what you mean by Proposed With Transition.  If you define your matchpoint with a non-destructive boundary in the Combined... surface before you paste the Proposed, then C3D will generate the transition by triangulating accross the gap, so to speak.

Proposed With Transition was just the name I gave the surface when the pasted in Proposed Only didn't match correctly.  Not that our proposed surface is all that difficult to recreate, but I'm a bit of a design pack-rat and wanted to save a copy of the original (just in case I screw something up) until I have a surface that works the way that I think that it should.  So I copied Proposed Only, renamed, and started trying the method with the offset/draped breakline.

 

I think it depends on how you have set up the match point.  If you don't want to start over again, try drawing a feature line where you think it should be matching.  Do 'Elevations from surface', pick the EG and add verticies.  Then add the feature line as a standard breakline to the Combined surface.

 

As said, don't think you need a Proposed With Transition.  Just edit the Combined surface.

 

I'll try doing this.  Thank you so much for all of your help.

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troma
Posts: 2,519
Registered: ‎05-21-2008
Message 7 of 12 (390 Views)

Re: Surface "Blending" Issues

11-16-2012 05:49 AM in reply to: sumanthap

Glad to help, let us know how it goes.

 

One caveat to the above: if you are proposing a major grade change, and you need to match the existing with a retaining wall, you can't just expect the transition to work.  Or if there needs to be a slope that you need to have control over (eg max slope 3:1) I would handle this with a grading group.  Draw a feature line, target the existing surface with a slope, and use automatic surface creation to make a slope surface.  Then paste this slope surface onto your final Combined surface.


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Active Member
sumanthap
Posts: 7
Registered: ‎05-13-2009
Message 8 of 12 (345 Views)

Re: Surface "Blending" Issues

11-19-2012 03:41 PM in reply to: troma

It didn't work.  We don't have a retaining wall, but we do have a streambank...  which, I've come to realize, might as well be a slightly angled retaining wall.

 

We have created a grading group for bank grading, and we can create a breakline from a feature line to define the thalweg, but beyond that I'm not sure how grading groups would work for natural channel design.  As in, I don't know other than the thalweg, how to define a riffle/pool sequence.  Any suggestions you can offer will be greatly appreciated.

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troma
Posts: 2,519
Registered: ‎05-21-2008
Message 9 of 12 (329 Views)

Re: Surface "Blending" Issues

11-20-2012 05:57 AM in reply to: sumanthap

What is a thalweg?

What is a riffle/pool sequence?

Are you tying into an existing stream, or designing a new streambed?


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Active Member
sumanthap
Posts: 7
Registered: ‎05-13-2009
Message 10 of 12 (325 Views)

Re: Surface "Blending" Issues

11-20-2012 06:27 AM in reply to: troma

The thalweg is the deepest part of the channel.  It's not always the center of the channel - in fact, depending on the planform, iit usually isn't in the center.  And to grossly oversimplify a riffle/pool sequence, streambeds aren't exactly flat - they have ups and downs with a general downward-trending slope.  Page 15 (of 24, TS3E-11) of this supplement to some design guidance illustrates that.  The area at a "peak" where the water isn't that deep is the head of a riffle, and the area at a "valley" the water is deeper is a pool.

 

We're tying into an existing stream, but we are changing the planform - so we're filling in some of the existing channel and trying to get the stream to flow a slightly different way.  The upstream and downstream ends of our project area do share elevations with the existing streambed, though.

 

Thank you again for your help!

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