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From: Barry-H
Network works
Cheers
Barry
Revised version to allow for differences of underside from top side.
Projected straight lines onto original solid to get cross sections & outer profile.
Divided cross sections on intersection point.
Select all and network.
Image Attachments:
Screenshot (245).png
From: Michael Gibson
Hi Bravlin, it can be difficult to create sort of blobby melty all-over-smooth shapes like that in a CAD program like MoI where the focus is more on precision. Sub-d modeling is probably a better approach.
- Michael
From: Bravlin
Thanks for such a quick feedback guys.
I examine Karsten approach to this shape reconstruction.
At first glance everything looks great. But i found surface artifacts.
I expect that some of them may be solved if we try to make profile curves (or rail curves) of equal density.
But unfortunately it doesn't help much. I thinks about blend use but not quite sure. Since blend and main shape
have different surface density and wires, i guess it may cause problems later when we would try to add details on section between blend and main shape.
I would examine other approaches a bit later.
Image Attachments:
ALG_001.jpg
From: Michael Gibson
Hi Bravlin,
re:
> I examine Karsten approach to this shape reconstruction.
> At first look everything looks great. But i found surface artifacts.
The first one looks like only a display artifact, not in the actual surface. If you export to a mesh format and make the mesh higher density it should go away.
It's a type of artifact that happens when the display mesh ends up with some sparse longer triangles across an area where the normals are changing.
The regular viewport display is more tuned to generate display meshes quickly so that you don't have wait extra time on every modeling operation. To get a better view of surface quality you can set up a keyboard shortcut that does a SaveAs to a mesh format like: SaveAs c:\bugs\test.obj then crank up the density and cancel when you're done without actually writing the file.
The other one though running through the centerline looks like a tangent discontinuity. That could be improved by trimming away some space and putting in a G2 blend surface like in the attached version.
- Michael
Attachments:
SRCSHAPE2.3dm
From: Bravlin
Ok. Moving forward.
I tried network approach by Barry-H. It's pretty straight forward. Network have useful options to tweak result shape via Custom and Uniform mode.
Network also doesn't rely much on a profile density so you may use dense and not evenly spaced curves.
Unfortunately result shape builded by network operator have one of artifacts i mentioned earlier.
I tried to export this shape to .obj and i have one additional question.
- " How should i export this type of geometry (botomm right shot) ? "
If we leave vertex with such high valency it definitely cause artifacts on render.
Attachments:
Q001NETWORK.3dm
Image Attachments:
Q001.jpg
From: Michael Gibson
Hi Bravlin - high valence worries is something that applies to sub-d modeling, not to static mesh rendering as long as vertex normals are coming through and being used in the render.
But what can happen with network surfaces with poles are surface shaping defects with little ripples in the surface as different shapes shrink down and collapse to a point.
One technique that can help alleviate that is to include a circle before the pole in the network curves, that helps to even out shaping before things collapse to a point, see attached version.
- Michael
Attachments:
Q001NETWORK_2.3dm
From: bemfarmer
Should there be a small circle on the bottom side as well?
- Brian
From: Michael Gibson
Hi Brian,
re:
> Should there be a small circle on the bottom side as well?
Yes if you wanted that same location on the bottom side to look very smooth under close examination you would want to do the same thing there as well.
But if it's not going to ever be visible that might not be needed.
- Michael
From: Bravlin
bemfarmer, today i tried biconcave scripts. I can't see the benefits of this approach.
I guess it may be useful in some kind of procedural modelling session or node graph.
From: bemfarmer
Hi Bravlin,
The script is just a quick way to generate some 2d curves...
- Brian
From: Bravlin
Q_02:
Another one modelling question. It's about right patch creation.
Here is a test project. It has 2 layers SRC and WRK.
How should i construct patch on WRK layer so it look the same as on layer SRC (it has a bit curved profile).
I suppose that in such a case it's easier to create some kind of a curved plane and trim it, but each time
i tried it always have gaps and naked edges in result after join process.
I also tried "SeparateSelectOuterLoopsDeleteTrim" but still cant understand how to use it in rebuild(retrim) surface process.
I also noticed that when we convert edges to curves we should not rebuild result curve this way we have better chance to avoid gaps after join process.
Attachments:
Q_02.3dm
Image Attachments:
Q_02.jpg
From: nameless
Hi Bravlin,
I gave it a shot, but I had to clean up to a point that I started wondering which parts of the model are important and should be retained. There were multiple overlapping edges and some double faces all around the model which can make it difficult to select the right lines for the commands to work. How did you model the MDK enclosure if I may ask? I will give it a shot again later when I have some time.
Good luck!
From: Michael Gibson
Hi Bravlin, so unless you had a really specific need to do it this way you would not want to approach your modeling steps so that you have to fill in an area like that.
Instead you generally want to have extended pieces that then all get booleaned or trimmed to common cutting surfaces, that's the best way for things to match up.
For filling it in though, one way would be to use the "Patch" command in Rhino which fits a bendy surface to a set of points sampled along curves. However, it is often quite finicky to get it to be accurate enough to join cleanly. Since this one isn't too bendy it could work though. In the future I also want to add in a similar surface fitting mechanism into MoI as well but there is not one like that currently.
A little later here I'll see about giving you some steps for reverse engineering the extrusion.
But again, you don't want to build things in such a way that you put yourself in this situation of needing to build a surface to a hole like that. It's better to work with solids and 2D curves from the beginning.
- Michael
From: Michael Gibson
Hi Bravlin, some of the naked edges could be coming from some new bottom surfaces that no longer align with the original extrusion.
The process for reverse engineering the extrusion is kind of tricky, the steps are something like extract the edges as curves, prepare some cutting lines to cut away portions that are not on the silhouette, trim the curves leaving no doubled areas in the Y direction, then compress it in the Front view using the edit frame corner grip with "Flat" snap.
That will then leave the flattened silhouette which can be extruded. It's also good to rebuild it to reduce segmentation and also there are a few spots where control points get very nearly stacked up at the end of some curves and those need a little adjustment to move the first interior control point.
When that is extruded it is then accurate enough to be trimmed with those edges, except at the bottom where some new surfaces stick out a little more than they did on the original. 3DM model file is attached.
Here are some screenshots of the process. At some point I want to make a curve silhouette tool to automate these steps.
- Michael
Attachments:
Q_02_extrude_3dm.zip
Image Attachments:
Bravlin_extrude1.jpg
Bravlin_extrude2.jpg
Bravlin_extrude3.jpg
Bravlin_extrude4.jpg
Bravlin_extrude5.jpg
From: Bravlin
Today i tried this algorithm of patch creation and have problems with naked edges again.
Guess i missed something important in trimming process or in surface creation.
I assume that one of a steps should guarantee the right contact of result surfaces.
I just cant figure which one. I inspect the project you provide Michael. And it works like a charm.
So i recorded short video of whole process.
https://www.dropbox.com/s/8nms9s7buihvk56/2019-02-03_12-16-25.mp4?dl=0
I also add project file to inspect if necessary.
Attachments:
Q_02_ALG01.3dm
From: Michael Gibson
Hi Bravlin, I took a quick look at your 3DM file and it looks like you're doing a Loft instead of an Extrude perhaps?
The curves you are lofting between have some skew between them, so that's going to affect the accuracy.
I could see the skew by looking at this edge in the Top view, a completely vertical extrude should only show as a point in the top view:
And it looks like the top and bottom curves don't have aligned endpoints:
That method I showed previously is only applicable to reverse engineering a completely vertical extrusion surface, not one lofted between 2 slightly different curves.
- Michael
Image Attachments:
Bravlin_accuracy1.jpg
Bravlin_accuracy2.jpg
Bravlin_accuracy3.jpg
From: Bravlin
> That method I showed previously is only applicable to reverse engineering a completely vertical extrusion surface, not one lofted between 2 slightly different curves.
Yes. That's exactly why i use loft between two curve profiles.
I noticed that upper and lower edge silhouettes lie not on completely vertical line.
Can we solve such case without patch tool (inventor, rhino) ? If its not completely vertical ?
From: Michael Gibson
Hi Bravlin, sorry no you can't accurately build a surface that passes through several interior non-isoparam curves like that, other than the full vertical alignment case.
The main way to do it would be to approach it how you would have wanted to model it originally which would be to have your pieces here as an extended base that has flat ends:
Then you would make your bendy front face as an extended surface shaped how you want and then trim or boolean difference your base piece with that forming new edges where things intersect each other.
You want the edges you're trying to fill to be formed by surface/surface intersections, not by keeping them and trying to build a new surface that has to pass exactly or very closely to all of them at the same time. You can do that if all the edges you have to pass through are a 4 sided region so you could use Network but not when they are in the middle of the surface.
- Michael
Image Attachments:
Bravlin_base_piece.jpg
From: Barry-H
Hi Bravlin,
I un-trimmed your surfaces and found a problem wilt the 2 faces shown in the photo they do not extend far enough to be trimmed by the vertical planar. Anyway having overcome that I made a solid of the body (no cutaways) and a solid to Boolean subtract (with cutaways)
to get the finished Solid.
The difference between top and bottom curves is 0.19 don't know how important maintaining this is ?
I generated the curves similar to how you have done but then extended them by using the extend tool.
This allowed spare for trimming.
Hope this helps
Barry
Image Attachments:
Rebuild.png
Solids.png
From: Bravlin
Thank you for the effort Barry-H.
My question is more about approach and limitation i guess.
To better know the boundaries of a program and algorithms of work.
We established that secure patch creation limited by one plane without tilt.
For other cases we shall use other software (solid, rhino etc). Which have patch tool but also
have there own limitation by form and curvature of result surface.
Also thanks for reminder about negative shape boolean approach.
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