Draping with gravity a series of fixed length, connected, rigid lines over brep

Hi there,

I am a rookie looking to generate a method of simulating the bending geometry of strips, by simplifying them into segmented and triangulated wireframes.

What I would like to happen, is that from a fixed “spine”, these strips fell onto the brep and if all the connected lines remained fixed length, would be forced to take a certain “path” around the brep.

Although the file I am providing shows a grasshopper generated set of strips, this is not a priority and it would be okay if this was something I generated manually, to get the correct arrangement regarding lines vs points to use in kangaroo, as I am not experienced enough to have total control over this in GH atm.

I also understand this is likely out of my league for now, but would appreciate any guidance on how to create wireframes where the segments are fixed length. Simple directional guidance appreciated!

Thanks for your time, I have attached a a jpg of the test setup I was making, with the GH file.


strip draping.gh (41.3 KB)

Your method of creating the zig-zag connections between pairs of lines is more complicated than necessary and results in some duplicate segments. I simplified your geometry by ignoring the zig-zags and duplicate segments and considering only the line pairs, which I projected onto the brep and then shortened to match the original line lengths.

strip draping_2020Sep28a.gh (18.6 KB)

From here, it’s not too difficult to divide the resulting curves and recreate the zig-zag pattern you want.

Here are the zig-zags added after the fact (green group). The ‘Count’ slider yields only odd numbers.

strip draping_2020Sep28b.gh (30.8 KB)

I forgot one little detail. The zig-zags need Pull Curve to the surface, though they are so close that SrfSplit (cyan group) works either way.

strip draping_2020Sep28c.gh (39.3 KB)

If the intent is to exactly preserve all the segment lengths including of the diagonals, you can do it like this:
strip draping_lengths.gh (18.4 KB)
Press the reset button in the highlighted group, then increase the slider to enforce the hard length constraint.

If this is just about finding geodesic curves on the surface though, there are easier ways. These are curves which are locally as straight as possible in the space of the surface, and are useful when you want to lay strips which are straight when unrolled.
Under Curve>Spline, you will find the ‘Geodesic’ component, which takes a surface and start and end points.

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Thanks for the help guys.

Joseph, although the help about simplification is very useful, it doesnt move me towards the goal of representing strip geometry, as those projected curves will now meander like a river when flattened.

Daniel, I cannot access my rhino from my remote location, but having googled your use of the term geodesic this has already provided enough assistance keep me busy for a long time. Exactly what I was trying to do but didnt know how to describe it in one word. Looking forward to using the tools you have advised and continuing research with new understanding of the term. Describing the geometry precisely feels half the problem! Thanks


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