boundaries from 3dfaces (surface from 3dfaces)

[kbarnettza]

Windows 8.1

Civil 3D 2015

I hope I just missed a setting somewhere

As far as I know, when 3DFACE objects are used to build a C3D Surface, C3D connects all the points - making additional triangles.

To get boundaries I use: FLATTEN, OVERKILL, REGION, UNION

Then I add the boundary to the Surface, resulting in what expected from the start - no additional triangles. Is there an easier way?

Also, FLATTEN lisp is not very clever - it converts 3DACE to a set of flat lines - just wanted the Z values to be zero, looks like I will make a small macro to do this which will speed up the process a little.

Thx for reading.

Kevin.

[Karsten.Saenger]

Hello Kevin,
I am not sure if I understood you correctly: You have created a surface and you want to get the surface boundary?
If yes, there is an easy way to get the boundary of a surface: Select the surface and use AECCSURFACEEXTRACTOBJECTS in the command line.

[kbarnettza]

No.

Received 3Dfaces from survey service provider.

Need to build surface from 3dfaces

Start with this:

add to new surface and get this:

Many unwanted triangles in resulting surface

Could limit by adding build filter to not add lengths over certain length but thats still not the same as the data received.

To get correct boundary, need to : FLATTEN, OVERKILL, REGION, UNION .. lengthy process ..   : (  

[Karsten.Saenger]

I see what you mean.
As far as I know and unfortunately there is no easy and one click solution to get the boundaries of the 3D faces before creating the surface.
You can try and play with the surface creation setting - such as min./max. triangle side length or max. angle - in order to get better results.

[Lisa_Pohlmeyer]

But, you can limit those large triangles. Inf the surface properties, Definition tab, set the maximum triangle length to the desired value. That should give you a better boundary to extract.

[AllenJessup · Accepted solution]

Select all the 3D faces and use the LINEWORKSHRINKWRAP command. This will produce a polyline. It will be at a weird elevatioin but you can change it to 0. Sometimes this can cause a shif but it can be moved back to the correct area.

Allen

[neilyj666]

Why not try AECLINEWORKSHRINKWRAP after you have FLATTENed the faces?

Not perfect but a good start and obviously you should work on a copy of the data and paste the boundaries back afterwards. I just COPY the faces across by a suitable displacement, Save my drawing and then work on the boundary.

[neilyj666]

I've found this gives very weird results that do not honour the triangle sides and produces a polyline with extrusions (which cause problems) thus the method I outlined

[AllenJessup]

Flattening probably does give better results. I don't usually work with 3D faces so I just figured I'd try shrinkwrap and saw if produced what looked like a good polyline. I never actually used it as a boundary.

Allen

[neilyj666]

Yes when I first tried the shrinkwrap on faces I though it had worked until I zoomed in and the boundary was offset inconsistently throughout...:(

[kbarnettza]

Never heard of this command before, another hidden jewel, combine this with bpoly and we are away... thx a lot

[neilyj666]

.....but bear in mind my previous posts and the warning that without FLATTENing the faces the boundary does not hounour the edges of the faces - you will need to zoom in to see this.

[AllenJessup]

Yes. That looks like the constant shift I was getting. I was handling it with a Move. But your Flatten method looks better overall.

Allen

[glaslp]

The behaviour, described above

"It will be at a weird elevatioin but you can change it to 0. Sometimes this can cause a shif but it can be moved back to the correct area."

still exists in Civil 2018. So is it a bug or a feature?

[KDAddison]

I've been using LINEWORKSHRINKWRAP with various sets of 3dfaces to define surface boundaries.  It usually works pretty well but sometimes in returns "Failed to create shrinkwrap." with no additional information.  Any ideas what could be causing this failure?

[neilyj666]

I don't know why this happens but did you read the rest of this thread?

3D faces must be flattened first to honour the boundary correctly. If they are not flattened you may be lucky and they may create a boundary that is consistently offset to the correct side to be used as an Outer boundary but this is a bit of a lottery.

[KDAddison]

I have.  Going forward I've been flattening to ensure they honor the boundary (although I haven't yet noticed any inaccuracies without flattening)  For the cases where LINEWORKSHRINKWRAP throws the failed to create boundary result I've tried first converting them to regions, to 3d polylines, flattening from all three cases and strangely LINEWORKSHRINKWRAP always returns the same result.  Drawing the boundaries manually seems to be the only option for the cases where LINEWORKSHRINKWRAP fails.

[neilyj666]

---

@JoeCup wrote:

I have.  Going forward I've been flattening to ensure they honor the boundary (although I haven't yet noticed any inaccuracies without flattening) 

---

You may have to zoom in quite close to see any...

Some more suggestions:

1. Run MAPCLEAN and break apart crossing objects and/or
2. Draw a rectangle that encompasses all your objects and hatch inside it, then generate the hatch boundary
3. Try erasing the lines within your shrink wrap boundary that will not form part of the boundary to reduce the object count

[jim.poole]

Just come across this issue myself - anyone got anything better than the recent suggestions?

FLATTEN takes an age on several thousand triangles.

BORDER, REGION, UNION create peculiar effects.

SHRINKWRAP seems to perform a peculiar rotation of the collective surfaces / faces first. Almost sitting the shape in it's most stable configuration, allowing gravity to let it settle first, then circling it in this new plan view.

It's probably quicker to manually draw with a PLINE than any of the other ideas.

😞

[neilyj666]

I have nothing new to add except that FLATTEN works well for me with a few amendments

1. I usually do not attempt to FLATTEN all at one - use a crossing window and take several attempts; don't worry about selection overlaps after the first run.
2. Erase internal triangles using a crossing polygon selection to reduce the number to FLATTEN
3. Ensure you  copy the triangles by Displacement out of the area of interest and work on these