Jump to content

Create NURBS Surface from either loft or 3D Power pack??

Recommended Posts

Hi All,


Need some help on something.  I'm trying to model a pretty complex structure based on a drawing that I received from the vendor.  Unfortunately, I believe the original file was exported poorly, likely on purpose as its been a battle to get a drawing in the first place.


That being said, I'm trying to create some surfaces of the exterior of the structure.  I traced the main surface lines with NURBS curves, however, when I try to loft or "create surface from NURBS curves" it either fails or creates something that isn't what I'm trying to model.  


Attached to this post is a screen capture video of what I'm trying to model based on the NURBS curves.  I'm not understanding why it will not loft between all 4 curves.  The closest I could get is lofting between the bottom 3 curves but then it fills in some random curve up top.  I really need it to populate all 4 curves at those specific paths.  There is another bit of geometry, the curve in the middle that you can't really see, is curve the structure makes at that point.  I've tried dicing everything down and creating a surface and use that curve as a mirror line but I couldn't get a surface to be created in any way.


How do I get this to work?  I've made sure all curves have the same degree number as well as going the same direction as its "parallel" partner.  I've been through every video I can find and after almost 20 hours of banging my head against this I'm ready to give up out of frustration... except that's not an option.  Why can't I simply say create a surface using these 5 curves?


SO, some help would be greatly appreciated.  Thanks in advance.

Edited by rseybert
Link to comment

@markdd Thanks for the video.  I gave it a try and it worked for the most part.  The biggest challenge is that I need to keep the exact geometry of the edges.  It seems that every time I loft or create surface from NURBS curves it alters the perimeter, preventing an exact fit with the rest of the model.  Could that be the NURBS count or some other setting?  It would get even worse once I subtracted the lower potion to cut out the openings on the side.


That being said, I had to abandon that process due to timeline and stick with some of the original mesh geometry that we received.  I was able to clean it up and purge out all the 3D Polygons that were onto of the original mesh surface, likely came over in the import.  


My new question is this, how to smooth out the facets?  They appear in OpenGL as well as a final render.  I've tried changing the mesh smoothing options in the Document preferences with no luck but I believe thats not what I'm looking for here.  Pictures attached for reference.


Thanks again.

Screen Shot 2020-01-20 at 12.17.53 PM.png

Screen Shot 2020-01-20 at 12.19.16 PM.png

Edited by rseybert
Link to comment

Ah, the saddle-span tent..... I've spent way too much time trying cleaning up models of it. It is possible to make a close representation using NURBS, but it will have surface breaks because of the complexity of the surface. Try doing it in quadrants. Vectorworks is not necessarily the best option because you have very little control over the NURBS tolerances when making surfaces.


These days I just use the manufacturer's mesh model like you are. Its unfortunate that its so low res. I have the faceting in my renders as well.




  • Like 1
Link to comment
12 hours ago, rseybert said:

My new question is this, how to smooth out the facets?  They appear in OpenGL as well as a final render.  I've tried changing the mesh smoothing options in the Document preferences with no luck but I believe thats not what I'm looking for here.  Pictures attached for reference.


Are they actual mesh objects (rather than groups of 3d polygons)?


Also, have you tried fiddling with the OpenGL options (crease angle can be adjusted here as well as in document preferences)?



Link to comment

@rseybert - Sorry if this is too late to help.  But I was irked we couldn't get it to work, so mulled it over and came up with some proof of concept solutions.


Center needs Loft Surface - No Rail Mode

Ends need Loft Surface - One Rail Mode


Setup for both requires several NURBS Curves: fabric edges, central sag guide, several profiles.  Surface "ballooning" can be prevented if the profiles are evenly spaced (shown), or progressively spaced (but that's a more difficult task). 


Results shown are tolerable surfaces.  Because of the pointy truss, each loft results in a group containing two surfaces.


Without knowledge of the real world dims and parameters, these surfaces may not represent how the fabric actually tensions from the various supports and pulls.


My loft profiles are drawn by clicking 3 vertices onto the 3d Loci, therefore they are shaped as vwx NURBS curves.  They may not represent the actual fabric shape. If the profiles adjacent to that pointy support truss are fattened up a bit, some of the concavity can be reduced.  But it's a lengthy description to alter them, so examples here show the basic 3 vertex curves.





Saddle Center.png

Saddle Ends.png

Saddle Rendered.png


Edited by Benson Shaw
  • Like 4
Link to comment

Yes, lots of problems with all this! It's all an approximation. My 3 point NURBS may not be close to AsBuilt contours.


@line-weight - That ballooning is because (I think) the profiles are all planar so surface squeezes where the spacing is not even, esp realtive to the the truss lines formed from circular arcs. The intermittent profiles should probably curve towards the truss lines  Too hard for me to figure the perfect profiles.


And, MAINLY, I/we don't know how fabric tensions and stretches, the sag values, the pull point z values, etc, etc,  compared to these NURBS and other modeled surfaces. We don't even know if the mfg mesh model represents a close conformity to the installed tent.


If model accuracy really matters to a client (Tower inside? Fly a drone? Focus an image?), an existing installation could be measured for AsBuilt dims (point cloud?) and model conformed therefrom.  But even that would be questionable for some other installation - temperature at time of install, temp at time of measurement, fabrication/installation variance ( fabric assemblies,  pull point placement, tension, temperature, relaxation/stretch over use cycles, etc, etc, blah blah blah.)  Seems like the known parameters are the truss dims and the design sags. Every AsBuilt will vary.


Then we have the vwx edge faceting and vague conformity in the sweeps (see below). ( @Kevin McAllister pet peeve!) Arrrrg!


Some other ways to model this (all fraught with pain, suffering and lack of conformity to the actual conditions):


BiRail Sweeps with several intermittent profiles.

One Rail Sweep with several "horizontal" profiles.

Surface from Curves (just the edges, but duplicate them first) then Interpolated Surface to adjust the sag.

Probably others.




Lemme know if anyone wants me to elaborate the modeling processes. Maybe others have some better knowledge or process.




BiRail Sweep Setup.png

BiRail Sweep OGL.png

Loft Horiz Profiles Setup.png

Loft Horiz Profiles.png

Surface From Curves.png

Interpolated Surface.png

Edited by Benson Shaw
  • Like 3
Link to comment
  • 1 year later...
  • 2 weeks later...
On 8/22/2021 at 6:56 PM, Kevin McAllister said:

Ask Tentnology directly. They have a decent model.




Yes, I have reached out to them via email and phone. I have not heard anything back other than they really do not wish to share this file, privacy, etc. I am still hopeful. I have two customers whom have purchased this system and they do not have the file from Tentnology, only the pdf file.

Thank you,

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...