Why would this steep grade (0.02:1) to surface make this dragonback at the top through a curve? Besides being wrong, it makes it impossible to continue grading from the top.
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Solved by Neilw_05. Go to Solution.
I really don't understand what I am looking at. More information would be useful.
Christopher Stevens
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It's a SW perspective view. The brown grid in back is an existing surface.The gray is a wall face - a grading object rising from existing surface up to the top of wall elevation which is the pink corridor (actually a surface created by the corridor which is set to no display). As the wall face hits that top of wall surface in a curve, it pops up in nearly vertical arcs as shown.
Here's that corner in plan view.
Having a lot of trouble with this today.
looks like an errant feature line in the sidewalk
Joe Bouza
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Like Joe said, it's probably an extra feature line. Are you building that part of the corridor with an alignment/profile and is there a separate feature line being added to the corridor at that location?
Your second screenshot is harder to see, since you're zoomed farther out.
Could you possibly share the dwg file?
Sorry, I still do not have an answer.
Have you tried viewing the pink sidewalk surface in objects viewer? Is it flat, or is it rippled? (I suspect that it is flat.)
How tall are the arcs?
What is this model/view going to used for?
Does the Dragonback invalidate that use?
(That is a serious question. Only you know your answer.)
Civil3 3D grading capabilities are not perfect. Grading objects are toxic.
My 80/20 rule:
In AutoCAD/Civil 3D, especially grading, 80% of the desired result is achieved with 20% of the effort,
Achieving the remaining 20% of the result requires 80% of the effort.
To me, It looks like your model/view is a least 80% there. Is achieving the final 20% worth 80% of the effort?
I think you will need to share the drawing if you want further input.
Christopher Stevens
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Thanks for all the replies and thought.
The pink "sidewalk" is a narrow corridor (and accompanying surface) created by sampling eg along the bottom of the retaining wall, adding a top of wall profile and running a simple assembly. The surface created by it is a 'dummy' that I can grade to from an auto feature line associated with the alignment at a steep "grade to surface". The goal was to create a feature representing the top of wall that I could then grade to pad elevation, but because it dragon-backed it wouldn't continue grading from the top to elevation. Just freezing up. I tried dinking with the corridor frequencies with no luck.
I'm trying to present a few options to this home builder that balance the cost and living benefit of retaining wall height/configuration vs optimizing yard acreage and fill.
Attached is one of the final configs. I ended up offsetting the alignment a bit, exploding the offset a couple times, joining it into a polyline, offsetting it back very close to my top of wall featureline (from grading the wall face), creating a feature from it and raising it to the dummy top of wall surface. Then I graded 1½:1 from that up to pad elevation. But what should have taken me an hour and a half took me six and I had to jerry rig it 😐
This is a design file that I data ref out the several surfaces and paste a composite together to finesse a bit outside.
It did make it so I can fairly quickly update wall heights and earthworks volumes by hand tweaking the profile along with a couple head fakes.
Still happy to post the file if anyone's interested, but what I'd really like to know is best practice for setting up these types of grading projects. I find limitations in C3D that seem like they should have been handled by now (maybe they have!). In Hawaii we end up having a lot of properties on steep slopes with need for rock walls. Along with decent fill and usually having to crush your cut it can become very expensive. This one could easily be $120K just to create a buildable pad with 940 CY fill (mostly crushed lava).
Forgive me for not studying your file but it seems obvious to me what the problem is. The "dragon back" occurs when you have 2 or more featurelines with different elevations stacked on top of each other. The software modeling algorythm cannot handle that situation. Since you mention you are trying to model a wall, I think the problem is you have the top and bottom of wall featurelines on top of each other. That is a no no in C3D. You MUST have a small offset between bottom and top of wall for it to work. Try offsetting the top of wall maybe 0.1' back from the bottom of wall. That should fix your model.
P.S. Be aware that very small offsets may not solve the problem as the software may not be able to handle it. Try 0.5 to 0.1 as a general rule, particularly when arcs are involved due to the 3D tesselation properties around arcs..
P.S P.S. If you are mainly interested in earth work quantities (v.s. 3D renderings) you can set the top of wall offset =1 CMU block (typically 8 inches US). That is where your grading will meet the wall and will give you a reasonable estimate of the grading for earthwork quantities.
Are you using a projection grading for the top of wall? It may help to just use a free standing Featureline. At this point it seems there will need to be a CAD file for troubleshooting.
I just re-read some of your description of your workflow so you can disregard the question about projection grading.
OK. Thanks for your interest, Neil. This stuff will usually bug me, too, until I get it figured out. In this case - workaround - but I always like to know more details and seems to help adesk if it needs a bug fix or enhancement request.
I saved a view named D-Back Shaded to get back to it if desired. C3D 2019
Heres the file: D-Backed Grading
Interesting, your grading to surface coming up is the object with the waves in it.
If you steepen the slope of the grading the waves get taller which looks like it might be some sort of rounding error in the grading calculations due to how steep the slope is. Set the cut slope to 0.02:1 and the wave height doubles. Set the cut slope to 0.01:1 and the wave height doubles again.
If you examine the area at the top of the grading, the feature line created by the grading at the interface with the target surface _wall1, you will see it is nice and smooth.
If you create a surface and add the grading featurelines as breaklines you get a nice smooth surface without any waves.
It appears that the issue is only the appearance of the grading object.
Interesting. I was wanting to then grade that top of wall featureline (from the grade to surface) up again to pad elevation at a 1½:1 and it just wouldn't grade. It would freeze, even left it overnight one eve. I made a few different efforts with no luck and figured it would grade further because of the arcing at the top.
I've encountered this behavior before. It's been a while so I don't recall what I did to deal with it. Try extracting the top of wall featureline from the grading (move it to a different site to extract it).
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