T Spline Surface Self Intersects

[Ramya Bradbury]

Thefile I have uploaded is for a quick conceptual architecture piece for school. Unfortunately I've got stuck at the error message in the title and cannot progress into the model mode. Essentially I want the sculpt body to intersect itself but it doesn't work so simply, foolish of me really aha! So I need to find some way of combining the two? So that it is one body not an overlap I guess?

Anyway I found this forum, where they seemed to be experiencing the same problem that was in fact solved, however I'm so inexperienced that I am unable to follow the instructions, namely the first one to start with; splitting the body (whilst still in the sculpt environment I can only assume?).

I would be really grateful if someone could help me; I'm finding it hard to progress with my project and CAD further ideas when I'm unclear as to what is possible and achievable with my limited abilities on the software.

Ideally I wanted the more defined intersection appearance rather than the blend between the two if that makes sense, the whole body's form seems to have changed a little in the process too. I had been checking box mode as I have seen that instructed in videos. Although I wasn't able to find a video about producing purposeful intersections (presumably because I've gone about this the wrong way) so really didn't know what I was supposed to be looking for in box view. I had always intended on the intersection; since it was my first time using it I didn't know it would be an issue unfortunately.

If you need sharper edges to have it appear as two more cleanly intersecting pieces, you could simply crease the edges and visually align the geometry so it appears as two surfaces intersecting each other.

I can sort of see what you did in the timeline and am going to have a play around with the original model to see if I can replicate what you've done so I can understand fully. I predict I'll get stuck to if you could perhaps give uploading the screencast another go that'd be really helpful!

To briefly explain the star-point errors. A star-point is any point that has 3, 5, or more faces all converging at a single point, essentially making a star shape. If the star is yellow that means everything is good. But, if a star is red, there may be a problem with an edge/face not being tangent or collinear. Star points also determine how a t-spline will be converted to BREP. When a t-spline is converted to BREP, it will split into separate surfaces at each star point.

EXT

Entities in set: 1

Specify height of extrusion or [Direction/Path/Taper angle]:P

Select extrusion path or [Taper angle]:

Modeling operation error:

The sweep results in self-intersecting surface

Error occurred during extruding.

I have never understood this limitation of the _Sweep command. Nor do I understand why only certain paths in the example result in self-intersecting surfaces. But in your shoes I would not use splines for the paths. Using 'normal' filleted polylines is the more logical choice I think. It will fix the issue you are having. And polylines are easier to dimension.

Another reason for redoing the paths: there are some disturbing inaccuracies in the drawing.

Self-intersecting geometry can occur if a path radius is too small for a large profile.

doesn't seem to be the case here, at least as it looks for expected geometry.

So I think it is a problem inside of the path object, where arc and line components

meet, like small overlaps or multiple vertices at one point.

Roy,

Thanks for taking a look & the advice.

I was able to draw a continuous pline for the new path & yes I found the "disturbing inaccuracies"

The plJoin would not work as I drew the original lines in varying UCS, but this attempt worked.

I think I'll start from scratch to fix some errors in accuracy.

This is only my third 3D project this year so obviously, I need more practice with this.

The DmThicken did not seem to have a path option, so I'm at a loss as to how it would work.

My first attempt I drew lines in two different UCS & then the PLjoin would not work but the JOIN did but created splines.

When I drew pline tracing the existing I got a pline I could use for the path.

I think created my own problems when I created the paths incorrectly.

I'm trying to create a region out of a closed polyline and it keeps telling me I have self intersection. What is a self intersection? I'm guessing it means the polylines criss-cross at some point, but I don't see any such thing anywhere. I would I find it?

Try to select the polyline and go to the PROPERTIES window (CTRL+1). Under the GEOMETRY you have the properties of the Vertex1. Click the field where says Vertex1 and you see two arrows pointing to left/right. Press one of them and you can see the other vertexes. Watch the screen and you will see a mark "walking" on your polyline. Sometimes you can see the place where "something is wrong" just watching the order and the position of the vertexes.

you can also (if whatever autocad you're using has it) shrinkwrap it, then just delete the old pline, or draw a rectangle around the pline, and bpoly in the rectangle; it will draw a new pline around the old pline.

I haven't had a chance to test your routine, but I'm really excited about it. Sometimes, when i extract the boundary from a surface (to then alter & set as my surface boundary), it will tell me give me my polyline intersects itself. Generally shrinkwrap will solve the problem, but there are the situations where that won't do it (the new pline shrinkwrap creates will intersect itself).

ASMI's code has been a great help with the VL which I am just starting to get to grips with. I was always against using it and usually just resorted to the DXF code approach in most cases. But now that I have dipped my toe into the world of VL, things are a lot easier to manipulate with a lot less coding.

yeah, until recently, i always just accessed the DXF library and did my coding from there. with our switch to 09 and beginning the usage of multileaders and annotative text, i realized a lot of my entmod routines didn't work. i looked into accessing the information through vla and soon realized that once you get the hang of how to retrieve the information, VLA is beyond powerful and so much better. i was able to completely rewrite (from scratch) several routines in one night; completely written in VLA.

Calculation of intersections is not difficult when the surfaces have a regular parameterization and are not near parallel along intersection curves (transversal intersection). However, if the parameterization is not regular, or if the surfaces intersect in regions where the surfaces are parallel or near parallel, intersection calculation gets challenging. One ambition of the GAIA II project has been to provide more accurate solutions for such intersections than what has been available by exploiting teh potential of approximate implcitization.

After the GAIA-project ended we have stabilized he prototype intersection algorithms. However, still the time is little early for industrial use as the approach is computational intensive. However, with the introduction of heterogeneous many core CPUs sufficient computational performance will be available for industrial use. Topics now addressed are:

Isogeometric analysis replaces the boundary structure type CAD-model, by modelling with trivariate rational spline volumes. Consequently the intersection of trivariate spline volumes will have to be handled. The current examples of isogeometric analysis avoid the intersection challenges by directly creating correct models. However, before the isogeometric analysis can be deployed in industry on large scale better approaches for model creation should be devised.

First draw the self intersecting spline in sketch and then extrude in Generative shape design, I would like to trim that surface which are self- intersecting to each other.

I attached screenshots with it for reference.

I've been experimenting with some geometry in GH, and have created a twisting tube spiral shape. For my project, I need this to be one solid shape, but the way I have created it means it passes through itself multiple times. Is there any way in grasshopper to create a solid form just from the overall external shape, rather than having it intersect itself (almost as if I were making a mold). I'm really stumped on this one, although I admit I am not an expert by any stretch

Progress is made - but since there's no IntersectWithSelf method available for Breps/Surfaces [as is available for Curves] the "key" method used (not available as component) is the notorious - and not recommended at all - Brep.MergeBreps method where you do the following paranoid thingy: you merge a Brep (pipe's BoundingBox as Brep) with a flipped Brep (pipe): if this makes any(?) sense(?), that is ... he he.

However it's highly questionable what Rhino means with regard manifold "solids" ... or the fact that a untrimmed Surface (pipe) is evaluated as closed Brep (Rhino) and ... er ... hmm ... reported as untrimmed Surface (GH).

Hmm ... due to hideous delay time(s) I think it's worth trying Plan B (the HocusLocusPocus option, that is). Shown the "section" option (spot the "part" missing from the orange pipe that is NOT // to section plane: meaning the good news):

The new Cocoon marching cubes plug-in affords a list of metaline field strengths along its length. I extracted the isocurve your model features along its length to approximate your missing center curve.

One method I was trying to work was to shatter the spline, make a tube of each segment, and then boolean union them. I cannot however get the variable pipe to work over the whole spline, and am not sure whether this method would work anyway

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