local_co-ords

[3__]

simple question:

how would go about I rotating several

primitives about thier local x-axis?

the primitive sop seems to work using world

co-ordinates.

-cpb

[Jason]

I assume you're talking about in SOPs ; can you tell me what is the local axis of a bunch of polygons? Primitives and poylgons are just points in space without their own transforms, so a local axis couldn't exist, right?

Am I understanding you wrong?

(In objects, use the Objects tool and not the Transform tool.)

[3__]

this is going to be another 'but in max...' replies

but let me first confirm with someone who better

understands how it works first...

-cpb

[Stremik]

Doesnt "Transform Axis" SOP do the job for you?

If not, try out Arbitrary Axis SOP written By Simon Barrick.

[hoknamahn]

I think cpb mean _coords_in_object_creation_moment_.

For example. Create a box, rotate them. Axises must be located in box edges directions. Then modify the box by Edit SOP and after that apply Transform SOP. You will see what new axises not collinear to old axises. But in many cases very usefull to have that "saved" old axises (and they we can call as "local" axises for any geometry).

[hoknamahn]

Illustration

P.S. cpb, you can use persistent handles as local axises. But it's not very comfortable in complex scenes.

[puma.snyder]

Please try this short example, maybe its what you want to achieve

Lay down a sphere sop and set it to Mesh,

append a convert sop

append a facet sop and set it to unique points

and finally append a primitive sop and put these expressions into the rotation params

and hit play

 explodematrix(rotaxis($F-1,cross(vector3(0,1,0),vector3($NX,$NY,$NZ))),"SRT","XYZ","RX")

explodematrix(rotaxis($F-1,cross(vector3(0,1,0),vector3($NX,$NY,$NZ))),"SRT","XYZ","RY")

explodematrix(rotaxis($F-1,cross(vector3(0,1,0),vector3($NX,$NY,$NZ))),"SRT","XYZ","RZ")

Hope this helps

Achim

PS: Credits for those expression go to Frank Firsching

[hoknamahn]

Much better to do it in 3dsmax style

Expressions in so simple business is improper

[3__]

The local co-ords for a face, for example are

inferred from the face normal and its first 2 edges.

I'm not entirely sure exactly how max does this as the

results can be a little random from one face to another.

Achim's code example is is not quite what I had in mind,

as can be demonstrated by inserting a transform in-between the

facet and primitive and rotating the sphere 45 degrees on

its Z axis before playing.

so I guess the short of it is: no houdini doesn't really do local

transformations.

-cpb

[meshsmooth]

I have been all maxed up so what is it you are really trying to achieve? Explain it in max terms and I will have a shot at translating it.

If you are talking about using local coordinates for vets or faces the only use full direction is Z the same as the normal, because the rest are unpredictable. I am looking at a teapot now with local coordinates turned on and I would only use the Z axes the rest are screwed.

When max dose this on one face it is ok because it ends up being in line with the sides of the faces. But have it work on more than one face or vertex and they end up solved differently and X from one face to the other has no relationship.

Z is the normal direction, so verbally how would you describe how you would have X aliened? X is the up vector. Where do you point the up vector?!

Houdini has some hope as making it better just because you can insert more logic and maybe even an up vector based on curvature. [An idea forming of a tool I could have a go at making, which would distract me from what I am trying to do at the moment]

[DaJuice]

It should be pointed out that in max, z is the vertical axis, and x & y are horizontal. Don't ask me why.

I haven't used max in a while, but if I remember correctly, when in local selection mode, if you select more than one face/point/edge you get multiple transform handles, one for each selection. And I think the handle then automatically aligns to the normal for the z-axis, but I'm not sure how the x and y axis are oriented.

[meshsmooth]

Max has Z up because it came from cad where the top view was the only view for a while and when they ventured into 3d Z was added to the "theoretical Z axis"