[Solved] Grid to sphere with Bend Sop

[sant0s81]

Hey,

in that post here, How to transform a sphere to a planar grid ? @magneto said, its possible to create a sphere from a grid with two bend sops.

The first bend works as expected. But with the second bend I only get strange results.

Does anyone know, how to do that?
Didnt want to write in that post since its from 2013

Thx alot!

Edit: Thats how it looks in Softimage

Edited February 12, 2020 by sant0s81

[sant0s81]

Friend solved it, thx Nico!

Only Capture Direction is different, rest is all the same.

edit: the grid has a size of 2:1 (in my case 8 *4) and is rotated 90 degrees on x.

Edited February 12, 2020 by sant0s81

[bradcarvey]

I tried this and was not able to create a sphere from a grid.

The first bend is a flat fan, not the start of a cylinder, based on the inputs shown in Salomon's post.  I can't think of a bend that  could make that into a sphere. I am using the bend setting from your picture.uld m

Could you share a scene file or more information on the second bend.

 

[sant0s81]

@bradcarvey

The grid has a size of 2:1 (in my case 8 *4) and is rotated 90 degrees on x.
Sry, forget to mention that.

edit: and yes, can share a file. How do I save out as hipc? Never was able to do that before.

Edited February 12, 2020 by sant0s81

[bradcarvey]

Thanks Saloman,

Rotating 90 degrees on the x, was important.

If you have a full houdini license, the default will be to save a scene as an hipc (commercial).  (File/Save).  If you have an indie license the default is hiplc (limited commercial) and apprentice is hipnc (not commercial)

[bradcarvey]

Note that if you reference the first bend angle in the second bend, you can get a nice animation of the grid morphing into a sphere. 

Grid_to_Sphere.hiplc

[sant0s81]

Hey, thx - thats cool.

I am also happy that it works finaly.

Best,
sant0s

[flcc]

Just a detail but as is, the bend values don't reflect the actual bending proportions. (bend1 angle x1 bend2 angle x2)

If you constrain the capture length to the grid size, then you get correct proportions, and most importantly you can change the grid size freely

Grid_to_Sphere F.hiplc

Edited February 12, 2020 by flcc

[sant0s81]

@flcc

Thanks for that improvement, gonna do it that way!

Cheers

 

[Atom]

Hmm... I find no evidence that either of these files produce a working solution.

Is there a bug in the Bend sop in Houdini 18.0.327?

What version of Houdini are you guys using?

[sant0s81]

@Atom

I am still on 17.5.

But your result looks really strange.
Did you try my manual way and changed the orientation to XY?

[flcc]

@Atom
I've buid it in H17.
Probably why it don't work in H18. But it's strange, traditionaly when a node change SideFX change node version.
And in this case it should load the 1.0 version, and It should working.

is there a version number on this new sop ?
 

[konstantin magnus]

You can spherify a grid based on its bounding box using VOP's 'from polar'-node.

spherify_grid.hipnc

[sant0s81]

@konstantin magnus

man, thats a level up... thx for sharing!

Wonder if there are more ways to convert a grid into a sphere

[flcc]

@konstantin magnus
Nice and simple set-up.
It make me understood the relbbox usage.

The VEX version.
However the "morphing part" is a bit strange with this solution.
spherify_grid vex.hipnc

by the way it seem frompolar doesn't exist in VEX.  I must use "view vex code" to find the way to use it.

 

 

 

[konstantin magnus]

Despite using sine and cosine you could transfer sphere positions via intrinsic UV coordinates.

sphere_pos.hipnc

[flcc]

Just curious, I try to apply this method to an object from real UVs, and I can't get it to work.
The best I can obtain is by promoting the original vertex uv to point uv but all I get is beautifull spiral on the sphere. At least it's not just a point .
an idea why ?

sphere_pos real uv.hipnc

[konstantin magnus]

While primuv() refers to intrinsic primitive coordinates, uvsample() uses the whole texture coordinates (no promotion to point attributes needed).

vector bb = relbbox(0, v@P).xzy;
v@P = uvsample(1, 'P', 'uv', bb);

Please look into this thread to see how you can cut the grid along the seams before applying it to another mesh:
https://www.sidefx.com/forum/topic/60740/?page=1#post-272057

sphere_pos_real_uv2.hipnc

Edited February 14, 2020 by konstantin magnus

[Atom]

Here is another offering.

Three UV mapped spheres that unfold to different grid aspect ratios. A 16:9, 4:3, and 32:9.

These are pre-animated Alembic files, not procedural at all.

ap_UV_spheres_unfold_to_plane.zip

[flcc]

Thanks Konstantin
I've checked the link examples, but I really miss something here.
I' probably don't fully understand how houdini handles UVs.

First : I don't really understand what intrinsic uv mean. Thus I dont really understand difference between primuv and uvsample. May be a language problem. For me intrinsic mean  : "Which is contained by nature". is it uv created or calculated on the fly ?
Second : Your last exemple work with grid -> rubbertoy but not with rubbertoy -> sphere, more precisely
don't work with respect to original uvs. You use relbbox to create new "pseudos" UVs, while UVs exist. why ?

Third : I made a very simple example to illustrate. While I've begin to study  the link examples and I kind of understood what is done,  I still don't understand why in this very simple example uvsample don't work. neither with point uv nor vertex uv.
- is uvsample should be run in a vertex wrangle ? (seem not)

I need to dive deeper in the exemples but some light should be welcome.

Thanks for the help

Cube to sphere.hipnc

Edited February 14, 2020 by flcc