Please, I need a hand ; I have been struggling so much doing an offset of a mesh

Replies to This Discussion

Permalink Reply by MAURO on January 14, 2015 at 10:38am

sorry I meant "isosurface"

Permalink Reply by martyn hogg on January 14, 2015 at 2:12pm

Do you need each strut of the final mesh to be a square section?

I think what is going wrong is that your picture frame mesh has no thickness so when you offset it or thicken it, Grasshopper or Rhino does not know what to do at the corners where all the mesh edges meet. Also it does not know which direction to offset or thicken and be able to join together all the offset mesh faces.

It might be easier to thicken the wireframe of the mesh using Exoskeleton and starting from just the lines made from the edges of the mesh faces but you are limited as to how thick you can make the mesh before problems occur.

I've attached a definition with the Exoskeleton component. You can see that if you make the strut radius too thick you get an error because some struts get engulfed by the mesh at the nodes. You need to add the exoskeleton component for this definition to work.

You can get a nice mesh by smoothing the output from Exoskeleton with weaverbird but I'm not sure if this si what you are after - It looks like you want a structure with very even, constant sections?

Attachments:

• issue.gh, 13 KB

Permalink Reply by MAURO on January 14, 2015 at 4:04pm

Thanks martyn for you time and answer  ! I've just downloaded exoskeleton. It's a nice tool indeed but the way it links all the edges don't match what I had first in mind.

It will be great if each struts of the final mesh remain "square" as you can see in the second picture.

I managed to unify, in the reference mesh, the mesh normals in order to offset towards the inside of the structure.

But still, impossible to get grasshopper offset the mesh faces according to their normals and scale down the result in order to avoid and get nice and sharps tri-dimensional edges (same as the picture 2)

Also, I used, in a fist time, the component wbFrame to generate all the triangle frames of the initial mesh, but one more time the result is not even on every faces and the thickeness or distance seems to change (see the bottom of the leg).  Maybe is it possible to do it a another way and instead using wbframe, offset each edges of every triangle frame ? so we get a nice and even frame?

Permalink Reply by martyn hogg on January 14, 2015 at 5:43pm

See if you can look into how exoskeleton works. There is info on this site about how it is generating the exoskeleton. David Stasiuk might be able to help.

It seems what you need is a specific exoskeleton with no smoothing. At Exoskeleton's heart is the 3dHull for creating the corner meshes that the strut meshes join too. To create the square effect you want, I think you need to control these corner meshes and join them with straight meshes.

I tried to recreate this by setting the polygon "Sides" parameter of Exoskeleton to 4 but there is probably more to it than that: I think it is to do with how those square strut sections blend into the corner sections... if you extruded squares along each strut line they would not blend nicely at the corners.... so how will that blend be constructed?

Permalink Reply by Daniel Piker on January 15, 2015 at 3:09am

Did you look at the 'cytoskeleton' component?
It gives square sections that might be more like what you are after. We also now included that component together with the latest exoskeleton release.

http://www.grasshopper3d.com/group/plankton/forum/topics/cytoskeleton

Permalink Reply by MAURO on January 15, 2015 at 6:01am

thx, I've just downloaded it but I cannot understrand how to get into the input "plankton mesh".

Permalink Reply by martyn hogg on January 15, 2015 at 12:42pm

I think that's because your mesh "Singlemesh" has some edges that are very very close together. I got rid of these lines using the Kangaroo remove duplicate lines component so i could feed a good set of lines into exoskeleton.

I'm not sure how you get a good mesh input for cytoskeleton from just lines. You could do it from polylines of the mesh face edges but you need to remove the bad faces that cause problems.

Permalink Reply by martyn hogg on January 15, 2015 at 12:59pm

There's an experimental weaverbird component called Mesh From Lines!

This gives a good input for Cytoskeleton

Attachments:

• issue.gh, 15 KB

Permalink Reply by MAURO on January 16, 2015 at 11:55am

Waou this is perfect ! thank you ! I managed to clean a bit more some bug lines here it's what I got.

Permalink Reply by martyn hogg on January 16, 2015 at 12:36pm

Great! Now I can see what you were trying to make!

Are you going to make it for real?

Permalink Reply by MAURO on January 30, 2015 at 9:13am

I could have if the projet was chosen, but unfortunately for me, only those 4 projects may get a chance to become 3D printed in their real dimensions.

http://www.hackkingsdesign.com/?page_id=21&lang=fr

Permalink Reply by MAURO on January 30, 2015 at 9:22am

Now I'm trying to get to understand grasshopper doing a finner job on thoses triangles and meshes, and still, I have an issu ! Maybe you could have a quick look ?

I reconstructed only a small part of the previous mesh and try to extrude it and offset it properply. In red is what I'm trying to achieve : Also, I'm not sure if I did well building up the grasshopper's components as I had a problem with the normal direction of one of the 3 triangles.

Attachments:

• triangle offset.3dm, 197 KB
• triangle offset.gh, 13 KB

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