## AutoCAD Civil 3D General Discussion

Valued Mentor
Posts: 684
Registered: ‎05-30-2005
Message 1 of 36 (936 Views)

# Offset a surface

936 Views, 35 Replies
04-07-2010 07:11 PM
Hey guys,
I have a interesting question here, I know there is a way to raise/lower a surface, but is there a way to offset a surface basically 1m (to make it easy) perpindicular to all grades? Because when you raise/lower a surface, if you have a 3:1 slope, it will raise/lower it verticall 1m or so, but then the perpindicular distance between the 2 surfaces is less then 1m.

If anyone has any ideas or any insight, that would be great.

Thanks
*Laurie Comerford
Message 2 of 36 (935 Views)

# Re: Offset a surface

04-07-2010 11:20 PM in reply to: Sindarin
Hi,

Fact of life. The perpendicular distance between the surfaces will only
be 1m when the surface is horizontal. Everywhere else it will vary. It
can also vary depending on which surface you start at and then go
perpendicular to the other.

On 8/04/2010 12:11 PM, Sindarin wrote:
> Hey guys,
> I have a interesting question here, I know there is a way to raise/lower
> a surface, but is there a way to offset a surface basically 1m (to make
> it easy) perpindicular to all grades? Because when you raise/lower a
> surface, if you have a 3:1 slope, it will raise/lower it verticall 1m or
> so, but then the perpindicular distance between the 2 surfaces is less
> then 1m.
>
> If anyone has any ideas or any insight, that would be great.
>
> Thanks

--

Regards

Laurie Comerford
Valued Mentor
Posts: 684
Registered: ‎05-30-2005
Message 3 of 36 (935 Views)

# Re: Offset a surface

04-08-2010 06:53 AM in reply to: Sindarin
Hey Laurie,

I was asking if there was a way to offset the whole surface so everything is 1m perpindicular distance
Valued Contributor
Posts: 90
Registered: ‎09-04-2006
Message 4 of 36 (935 Views)

# Re: Offset a surface

04-08-2010 07:38 AM in reply to: Sindarin
I had this same question a while ago. The consensus was it can't be done in Civil 3d. I'm not that familiar with other Autodesk software but it seems to me that somehow this should be possible. I tried making my surface a solid using the triangles and thought I could import that into another piece of software and offset (or extrude?) it, but I never found anything that could do this. I called our local Autodesk salesman and he didn't have any ideas either.

To make a long story short, I ended up offsetting my surface manually; which, in my case, wasn't too hard, it was just time-consuming.

Here's the old thread just in case it helps you some. I'd love to know if you find out anything. Good luck.
New Member
Posts: 1
Registered: ‎04-08-2010
Message 5 of 36 (935 Views)

# Re: Offset a surface

04-08-2010 11:37 AM in reply to: Sindarin
I was researching the same question...
it seems they have done it in civil3d 2011 with the command SURFOFFSET

i don't have 2011 yet so still looking...
*Laurie Comerford
Message 6 of 36 (935 Views)

# Re: Offset a surface

04-08-2010 02:18 PM in reply to: Sindarin
Hi Sindarin,

The discussion referred to by corbittshoffer and in particular the post
by Allan Jessup do describe how you can do it.

Allan's lisp program to offset the 3D faces is a start and you could
just build a model from the offset faces accepting that there would be
linear interpolations between triangle edges of the offset triangles.

Where the offsets are convex this would be an acceptable model.
Where the offsets are concave (ie at a valley or ridge line depending on
which way you are offsetting) you would have errors and you would have
to know your site and the level of error acceptability to determine what
extra steps to take to reduce the errors.

A viable manual method to improve the model would be to:
Use a display of the watershed boundaries to guide you as to ridge line
locations, or mirror image the surface and display watershed boundaries
of the mirrored surface to see the valleys as needed depending on
whether you are offsetting upwards or downwards.

In the concave situation, you could transform the crossing triangles to
regions and explode them back to 3D lines. Then trim the lines back to
the watershed lines and delete the 3D lines which are on the wrong side
of the watershed boundary. Finally build the new surface from the
trimmed 3D lines and the other triangles.

Alternatively you would need to follow the theory in the PDF file Allan
referenced and program the required result.

Regards

Laurie Comerford

On 8/04/2010 11:53 PM, Sindarin wrote:
> Hey Laurie,
>
> I was asking if there was a way to offset the whole surface so
> everything is 1m perpindicular distance
*Expert Elite*
Posts: 5,790
Registered: ‎05-21-2003
Message 7 of 36 (935 Views)

# Re: Offset a surface

05-04-2010 07:53 AM in reply to: Sindarin
Unfortunately that looks like it's basic AutoCAD command and will work on AutoCAD 3D surfaces not Civil 3D Surfaces.
Allen
Valued Contributor
Posts: 90
Registered: ‎09-04-2006
Message 8 of 36 (935 Views)

# Re: Offset a surface

05-04-2010 11:27 AM in reply to: Sindarin
So you would have to take the C3D surface triangles and convert them to an autocad surface and then use the surfoffset command? Is that the easiest way to do this?
*Expert Elite*
Posts: 5,790
Registered: ‎05-21-2003
Message 9 of 36 (935 Views)

# Re: Offset a surface

05-04-2010 11:33 AM in reply to: Sindarin
Sounds right and I don't know any other way to do it. But I don't have 2011 installed yet so I can't say for sure how well it will work. If you try it, let us know.
Allen
Valued Mentor
Posts: 684
Registered: ‎05-30-2005
Message 10 of 36 (936 Views)

# Re: Offset a surface

05-04-2010 11:34 AM in reply to: Sindarin
The way that I ended up accomplishing this was to take the feature lines used to make the surface and do a stepped offset of them. I am looking for a more automated way though.

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