Offsetting Surface

[Anonymous]

Hi guys, hoping you may be able to help me out.

Has anyone managed to find a way to offset a surface perpendicular to the surface, so as to achieve a minimum specified amount of fill (or cut)

A few useage scenarios I have been able to come up with would be;

- capping landfill with clay
- lining a clay dam
- stripping a specified amount of topsoil.

The process is quite straightforward (basic Pythagoras) when working with a planar surface of a constant gradient, but that is very rarely the case when dealing with these sorts of situations, and we need a method that can be applied when grades vary across a single surface.

What would be even better is if the tool could somehow allow me to add criteria, as often more capping is required on the batter than on the crest (or floor if talking about dams)

Often we are dealing with UAV data from the existing earthworks, and reworking the entire site back to an arbitrary design is not an option.

Thanks,

[Jowennl]

Hi,

I'm not sure what you mean by offset a surface perpendicular. Do you mean you want to have a copy of the same surface above and below?

If you want to offset vertical any surface please see attached animated gif. If not like this can you please show image of what you want to do?

Cheers,

Jowenn

[Anonymous]

Hi Jowenn,

Often engineers specify a minimum thickness of material to be placed perpendicular to a surface. Unfortunately a simple vertical offset cannot be used.

I have done a quick sketch for you, to show why  I believe that a simple vertical offset will not achieve the desired outcome.

[Jowennl]

Hi Dylan,

Now I understand what you mean. This is an interesting topic. Thanks for sending a photo to clarify. I think you should post this in idea forum to request a function like this. I normally see custom assembly can do something like that. See this <thread link> But that is for design assembly. In subassembly I can easily see it’s easy to do but in 3d surface and massive numbers of triangle an ability to offset that and will check each traingle faces would be a challenge. I don’t think that tool exist as of the moment but if it does i’m interested to see that as well.

Cheers,

Jowenn

[KMercier_C3D]

 This has been an idea for a while now. (LINK). If you scroll all the way to the end of the comments you will see that @joantopo had suggested SURFOFFSET but despite it having 'surface' in the description it does not appear to be for Civil3D surfaces. 

[AllenJessup]

I'd think that to use SURFOFFSET you'd have to convert the Civil 3D Surface to an AutoCAD Surface. I haven't done it in a while but I think you'd need to explode the Civil Surface to 3D faces and use those to create a Mesh.

[neilyj666]

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@AllenJessup wrote:

I'd think that to use SURFOFFSET you'd have to convert the Civil 3D Surface to an AutoCAD Surface. I haven't done it in a while but I think you'd need to explode the Civil Surface to 3D faces and use those to create a Mesh.

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....and then wait for several hours while Civil 3D thinks about it before crashing as it tries to cope with the number of triangles.

I've tried splitting the civil surfaces into various slope categories and then offsetting each by an appropriately amended vertical offset and pasting back together but there are weird overlaps and areas where the surfaces don't meet....it's a particular problem that I've never been able to solve with any success.

The process can be likened to blowing up a balloon as the surface of the balloon expands (offsets) with each puff of air....can't be done in Civil though...

[neilyj666 · Accepted solution]

Whilst this isn't directly possible with Civil objects it can be done with AutoCAD objects (as suggested by others) although the example below is VERY simple.

1. Create the finished Cvil 3D surface model of the landfill cell and extract the triangles
2. Optionally) Move then by a suitable horizontal offset away from other data
3. Select the 3D Faces and CONVTOSURFACE
4. SURFOFFSET (by -1 in this case)
5. XEDGES to extract Line objects at the edges
6. Select the line objects and move them to new layer
7. MOVE these lines back the the original location
8. Create a new Civil surface from the line objects.

This has worked in the simple example above and is based on my (limited) vanilla CAD 3D modelling knowledge. There may be a slicker way of doing it and it may also fall down/crash CAD if the original Civil 3D surface is complex

[Joe-Bouza]

For quantity?
I always pad my quantity anyway so the difference in the cos(theta) and 2d area x thickness has never concerned me

[Anonymous]

Probably not best way but....

I would suggest to create cogo points on your surface to offset and and add these points to your new surface definition.

use Lower/Raise edits to adjust Datum would create an exact offset of your surface.

[Joe-Bouza]

Wow!
Design slopes steeper than 1 on 1?
Couldn’t you just multiply the 3D surface area by the thickness?

[neilyj666]

I can't see how this is any different to simply applying a raise/lower to a surface; the points are merely being moved vertically whereas the OP wants them to be offset perpendicular to a surface refer to my post about blowing up a balloon.

[Anonymous]

Spot on Neilyj!

Perhaps it would help if the people responding understood the "why" rather
than the how. (Although I am pretty sure I have already explained it in
this thread)

Often an engineer, or manufacturer will specify a minimum thickness of a
liner, or capping layer on a dam or landfill respectively.

This minimum thickness is specified as being perpendicular to the surface,
rather than vertically.

(P.S. I can do this in a Trimble equipped grader, so Civil3D should have no
dramas doing it)

[neilyj666]

I think my suggestion using vanilla CAD commands works well enough but the number of triangles in a typical earthworks model is likely to crash AutoCAD.

The only other workaround I can suggest is to split up the model into base and sideslopes and apply a vertical offset to the base and an adjusted vertical offset to the sides.

Then create a new surface and paste in the sides and the base - there may be some manual jiggery pokery at the join...!!!

[Anonymous]

Yes, your solution does certainly work on design type models, and models
with limited data, however as soon as I tried it with actual ground data
(even from a conventional survey, let anyone a UAV dataset) AutoCAD crashed.

[neilyj666]

Yes - I wouldn't even consider a UAV dataset for attempting this (or most things in Civil) as there is far too much redundant information (0.25m point spacing FFS)

[Muthya]

Just as an aside.

Is it possible to export the offset surface from Trimble grader to any file format. Say *.ttm?

[Anonymous]

I like your thinking... however not that I am aware of, could possibly do it using SCS900... but its an incredibly cumbersome and expensive way to do it...

[Muthya]

Thanks. Will check out possibilities.
Expensive???

[Anonymous]

Yes, I don't have a grader sitting in my office to use for design work....