Is it possible to compare a mesh before and after Kangaroo??... (explanation inside)

Hi everybody.

I want to study the ratio "length" divided by "initial length" for each edge of my mesh.

But here is what I have :

After only one iteration, my mesh is nearly unchanged. So I should have an interval between something like 0.999 and 1.001. This is not the case...

My explanation is that Kangaroo re-order (or re-label) each edge while computing.
Thus, my division doesn't make sense because I am comparing the length of 2 different edges. Am I right?

Furthermore, does anybody think of a tricky way to do it??

Thank you guys

Tim

Replies to This Discussion

Permalink Reply by TimFLM on June 13, 2012 at 9:51am

=> Actually this is precisely what I want to do !!

http://vimeo.com/8850556

How did you do this Daniel?

Thx!!

Permalink Reply by Giulio Piacentino on June 13, 2012 at 10:15am

Hi Tim

in Rhino meshes, the constants are faces and vertices, as the representation is so-called face-vertex. My guess would be that in the video a list of lines is compared before and after the process. However, you could also use wbFacePolylines and explode all faces, as the order of faces is invariant.

I hope this helps.

Permalink Reply by Danny Boyes on June 13, 2012 at 9:56am

What are the components after your red arrowed Mesh components?

If they are Giulio's Mesh Edges then I have seen somewhere that a bug causes the order to vary

Permalink Reply by Giulio Piacentino on June 13, 2012 at 10:07am

Danny there is no bug,

edges have no a priori predefined order, as they are computed, not stored. I'll have a look at the definition though.

Permalink Reply by Danny Boyes on June 13, 2012 at 10:13am

Apologies for the libelous accusation! I was just recalling (badly) a discussion from sometime ago. :)

EDIT: I retract the bug statement and replace it with quirk

Permalink Reply by Giulio Piacentino on June 13, 2012 at 10:43am

About quirk, maybe. The script below here does a better job in this case, I hope, but is nevertheless not perfect. A mesh with exactly the same appearance could have another order, too. The face-vertex mesh representation just does not store the information, so the choice of how to return the lines could possibly be referred back to point order or face order. In the case below, the face order is used.

Permalink Reply by Giulio Piacentino on June 13, 2012 at 10:55am

Btw, Weaverbird Mesh Edges on the other hand uses geometric invariance - meaning that meshes that look exactly the same will have edges ordered the same, no matter how faces are stored.

Permalink Reply by TimFLM on June 13, 2012 at 10:11am

It is the Weaver Bird "mesh edges" component !

Permalink Reply by Daniel Piker on June 13, 2012 at 11:02am

I would also recommend to input lines (rather than meshes*) to the Geometry Input of Kangaroo if that is what you are interested in comparing.

So you could use the WeaverBird MeshEdges to extract the lines before simulation, as they are then tied to particular vertices there is no issue about ordering of the output, even when the geometry changes with the simulation.

for an example of measuring stresses try this discussion:

http://www.grasshopper3d.com/group/kangaroo/forum/topics/getting-sp...

*You can also input the mesh to Geometry as well, in a different data path, if you need that.

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