Delete Edge problem ?

[sebkaine]

Hi Guys ,

I would have a dumb question , and i have created a dumb scene to illustrate it ...

I am trying to create a nurbs curves from a simple selection of edge. An optimistic person would have think ....

- select the edges

- delete the non selected edges

- convert them to NURBS cv.

BUT the delete sop doesn't give me coherent result (cf attach scene).

So after some research i would like some confirmation from expert Houdini Mind about edges in H ...

It looks that edges doesn't has any physical existence in houdini. they are just a diplay gizmo that the user can manipulate , but at the core of the soft , when you move an edge you only move point , and thus you move the vertice attach to this point and thus the primitive attach to those vertices. But the edge that you think you manipulate is only a scam ... in reality ? is that correct ?

So when you make a selection of edge or a group of edge , you are selecting something that doesn't exist in the geo, in reality you are only selecting the point and the vertices represented by this fictional edges ? is that correct ?

So my question is why the delete SOP offer you this delete Edge Option , as it doesn't do what it is suppose to do ? it only delete the point and thus looks to be redundant with the delete point option ? Could you give me an exemple of a situation that justify the existence of this edge option in the delete SOP ? To me , and i must be wrong , this delete edge option looks to be redundant and useless, and worse it drive you on incoherent result (well in the mind of a twisted maya guys .... )

Many thanks for your lights guys !

Cheers

E

deleteEdge.hipnc

Edited November 22, 2013 by sebkaine

[magneto]

Yes Houdini doesn't have real edges like other 3d software where edges can directly be accessed by integer ids. It's the same reason we don't have edge attributes.

Resident experts would know more about it but from what I read they didn't add them early on, so now adding them would be a huge undertaking. I attribute this to edges not being that useful back in the day before edge loop polygonal modeling became popular in early 2000s I believe.

Edges in Houdini is still pretty good though. If you want to delete an edge, you have to use the Delete SOP, but to remove an edge, you have to use the Dissolve SOP.

[sebkaine]

Thanks for your Help Ryan ! The dissolve tool is exactly doing what i was expecting with the deleteSOP

I'm still confuse by the edge to curve workflow in H.

For NURBS it looks that the concept of Isoparm doesn't exist , so you can't directly extract a curves from a nurbs object ... as a nurbs obj is only point connected to form a patch.

So i haven't find a way to simply extract curves from a NURBS obj yet.

For POLY the various post i find on odForce converge to the same tricks

- you make a group of point

- you sort them with various method (group order / sort node / custom neighboor or distance evaluation)

- you use a add sop to create the poly cv

- you convert to NURBS

It's a pretty geeky path to exctract a curves ...

I would like to be sure that it is the default workflow in houdini to solve this problem ?

Thanks again for your time !

[malexander]

Use a Carve SOP and set the operation to "Extract". Then you can generate a NURBS curve in either the U or V direction.

[sebkaine]

Thanks for your help Mark it works perfectly ! More over this carve node looks to be what i was searching as a motion path SOP level ...

I've made quick scene that sum up the technics i've learn for extracting curves from geo. If you have better tricks ... i'm interested !

edgeExtract.hipnc