point coordinate?

[ehsan parizi]

So we have point position and normal, but do we have anything like point coordinate system?! how do we define the rotation for a point?

[anim]

either by "N" and "up" vector attributes

or "v" and "up" vector attributes

or "orient" quaternion attribute

or "rot" quaternion attribute (it ads to any of above mentioned)

it depends on your needs, all mentioned methods are automatically recognised as rotations by Copy SOP and Instancing and at some other places in houdini

apart from that you can define point coordinate by any means you want, since you are the one who will be using it later

so any custom quaternion or matrix3 attribute will do

[ehsan parizi]

either by "N" and "up" vector attributes

or "v" and "up" vector attributes

or "orient" quaternion attribute

or "rot" quaternion attribute (it ads to any of above mentioned)

it depends on your needs, all mentioned methods are automatically recognised as rotations by Copy SOP and Instancing and at some other places in houdini

apart from that you can define point coordinate by any means you want, since you are the one who will be using it later

so any custom quaternion or matrix3 attribute will do

Thanks Tomas,

Is UP 90 degrees from N?

I'm trying to define it in vopsop.

How does orient quaternion work? is there any kind of documentation on that?

Edited July 27, 2011 by ehsan parizi

[edward]

"up" should be perpendicular to N but is not strictly required. However, it must NOT be in the same direction as N.

The "orient" attribute works as any (unit) quaternion value defining a rotation. Without going into the math, you can think of it as an "axis-angle" encoding into 4 floats. The formulas for converting between unit quaternions and axis angle representation can be found on wikipedia. Note that in Houdini the quaternion is defined by (x,y,z,w) which is differently ordered from the wikipedia page which I think is (w,x,y,z).

For reference, http://www.sidefx.co...y/instanceattrs

[ehsan parizi]

Thanks guys, That was really helpful.