Re: [script] normal vector to xyz rotation?

[Alan Jones <skyphyr(at)gmail.com>]

Hi Peter,

Excuse my laziness I didn't real through all your code so I've no idea
how you're tackling this, but here's a simple approach I'd recommend
anyway (I'll explain the math rather than coding it out.)

Take the direction you want to be "up" on your object (probably the y
axis I guess so 0,1,0). Get the cross product of that with the normal
you want it to rotate to. The result is the axis you want to rotate
your object around. To get the angle you want to rotate your object get
the dot product of the up axis and the normal. Then get the inverse
cosine of this and that will be the angle in radians you want to rotate
it. The only problem you'll probably come into this way is defining how
it rotates around the normal. You may want to look at doing this with a
direction vector which could be global or using the U and V directions
or whatever.

Cheers,

Alan.

On 9/4/05, peterb <peter_b(at)skynet.be> wrote:

probably a lot of people here have tackled this one allready,

I did search in the archive and google, and a lot came up, but it quickly turns complicated, with matrices and all.

just hope there is a simple answer...

 

I would like to place objects on a mesh's points, oriented according to the normal.

getting to the positions is easy enough, finding the normals too.

but going from the normals to an orientation is less so.

note that I do not want to create a cluster per point, and use objtocluster constraint, which is going to give me the result I want.

in the end I want to be doing this with a lot of objects and also particles so making thousands of constraints doesnt seem right if all I'm after is "just a rotation"

 

any hints in where Im going wrong, and wether this is the right approach to the problem?

----------

set sel = selection(0)

set oGeometry = sel.activeprimitive.geometry

set oPoints = oGeometry.Points

 

for each pnt in oPoints

    set ("name" & i)

    oNull.Kinematics.local.parameters("posx").value = pnt.position.x

    oNull.Kinematics.local.parameters("posy").value = pnt.position.y

    oNull.Kinematics.local.parameters("posz").value = pnt.position.z

   

    oNull.Kinematics.global.parameters("rotx").value = pnt.normal.x

    oNull.Kinematics.global.parameters("roty").value = pnt.normal.y

    oNull.Kinematics.global.parameters("rotz").value = pnt.normal.z

next

-------------

now this is obviously no good for the normals/orientations

the normal is a vector, and the rotation are angles, so I cant just replace one with the other right?

 

I tried with radianstodegrees:

    oNull.Kinematics.global.parameters("rotx").value = xsimath.radianstodegrees(pnt.normal.x)

    oNull.Kinematics.global.parameters("roty").value = xsimath.radianstodegrees(pnt.normal.y)

    oNull.Kinematics.global.parameters("rotz").value = xsimath.radianstodegrees(pnt.normal.z)

but that doesnt look right either

 

so looked all over in the scripting reference

and noticed the existence of setfromXYZangles and GetXYZanglesValues.

are these what I need?

--------------------

set sel = selection(0)

set oGeometry = sel.activeprimitive.geometry

set oPoints = oGeometry.Points

for each pnt in oPoints

    set ("name" & i)

    oNull.Kinematics.local.parameters("posx").value = pnt.position.x

    oNull.Kinematics.local.parameters("posy").value = pnt.position.y

    oNull.Kinematics.local.parameters("posz").value = pnt.position.z

 

    set oVector = XSIMath.CreateVector3

        oVector.x = pnt.normal.x

        oVector.y = pnt.normal.y

        oVector.z = pnt.normal.z

 

    set ROT = XSIMath.CreateRotation

    ROT.SetfromXYZAngles oVector

    ROT.GetXYZAnglesValues X, Y, Z

 

    oNull.Kinematics.global.parameters("rotx").value = xsimath.radianstodegrees(X)

    oNull.Kinematics.global.parameters("roty").value = xsimath.radianstodegrees(Y)

    oNull.Kinematics.global.parameters("rotz").value = xsimath.radianstodegrees(Z)

next

----------------------

its different and doesnt look right either?