AutoCAD Civil 3D General Discussion

AutoCAD Civil 3D General Discussion

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Active Member
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Registered: ‎04-19-2007
Post 1 of 7

Subtract one surface from another.

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11-24-2009 11:10 AM
Hello all,

I am in need of subtracting Surface A from Surface B to display the surface intersections between the two. I have a geological top of clay surface and a bottom of clay surface where the bottom intersects with the top thus showing holes in a geological clay layer. I am wanting to know if Civil 3D supports the subtracting of two surfaces.

Thank you!
*Terry W. Dotson
Post 2 of 7

Re: Subtract one surface from another.

11-24-2009 12:21 PM in reply to: CAD_Avatar
brian_ranstead@urscorp.com wrote:

> I am in need of subtracting Surface A from Surface B to display the
> surface intersections between the two. I have a geological top of
> clay surface and a bottom of clay surface where the bottom intersects
> with the top thus showing holes in a geological clay layer. I am
> wanting to know if Civil 3D supports the subtracting of two surfaces.

Don't claim to be an expert, but you should be able to create a 'Volume
Surface', using care in specifying the order of base/compare surfaces.

Then contour elevation 0.0.

Terry
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Never start any job without the right tools!
AutoCAD Add-on Tools at http://www.dotsoft.com
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Post 3 of 7

Re: Subtract one surface from another.

11-24-2009 12:30 PM in reply to: CAD_Avatar
Terry, if you are just trying to get the intersection of the two surfaces, the order they are added (base vs. comparison) doesn't matter.

Brian Hailey
http://www.cad-1.com
http://www.AtYourDeskTraining.com
Brian Hailey
CAD-1.com
My Blog
*Terry W. Dotson
Post 4 of 7

Re: Subtract one surface from another.

11-24-2009 04:01 PM in reply to: CAD_Avatar
BrianHailey wrote:

> Terry, if you are just trying to get the intersection of the two
> surfaces, the order they are added (base vs. comparison) doesn't
> matter.

True, but todays 'just' is often tomorrows 'first of many', so might as
well build it right today.

Terry
--
Never start any job without the right tools!
AutoCAD Add-on Tools at http://www.dotsoft.com
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Registered: ‎11-21-2012
Post 5 of 7

Re: Subtract one surface from another.

11-21-2012 05:49 AM in reply to: *Terry W. Dotson

Terry

When i do what you say, the result volume surface is in the wrong elevation.

Example: my surface "1" is in (+-) elevation 235.600 and my surface "2" starts from 235.850 to 235.450 (it's like a cup), when i do the volume surface, the result goes to elevation 0.0 (+-), and when i do contour elevation 0.0, it gives me the interserction but in the wrong elevation! how do i put this in the right elevation? because what i want is the (surface 1)-(surface 2)

 

thanks for your time

 

Ivo Costa

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Post 6 of 7

Re: Subtract one surface from another.

11-21-2012 07:59 AM in reply to: CAD_Avatar
The elevation you're seeing is the difference in elevation between the two surface; surf 1 minus surf 2. This is what it seems like you asked for. So you have your contour line representing where they intersect and all you need now is its elevation to match the surfaces?

Turn it into a feature line and use the surface from elevation tool.
Matt Kolberg
Cansel - Autodesk Division
http://www.cansel.ca/
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Post 7 of 7

Re: Subtract one surface from another.

11-21-2012 08:46 AM in reply to: mathewk

If you don't have a good understanding of how Sites work within Civil 3D, I would recommend that you don't use a featureline, just use the same tool and assign the elevations to the polyline instead. If you want more inforomation on why I recommend this, check out THIS.

Brian Hailey
CAD-1.com
My Blog
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