[Maya-Python] object inverse matrix

[V126]

Hey guys,

I'm a noob, and am trying to understand how to use the inverse matrix
better. It's related to this thread so I'm replying here. I've searched
through all the documentation and posts and haven't found an answer (that I
can fully comprehend) yet.

My previous experience comes from maxscript, so I'll have to use it as
pseudocode to illustrate.

I've got three objects with transform nodes: "moon", "earth" and
"asteroid1". I want to save the translation and rotation of "moon" relative
to "earth" into a variable, so I can snap "asteroid1" to that exact
translation and rotation that the moon has, relative to the "earth". I want
to save it in a variable so I can use that relative position and rotation
in another file that doesn't have the "moon" in it (therefore I can't cheat
and just xform "asteroid1" to "moon").

Here's how I did this in maxscript pseudocode:

# Get a transformation matrix of the “moon” to the “earth”.

my_matrix = moon.transform * inverse earth.transform

# Then use that matrix to snap the “asteroid1” to the location I recorded
relative to the “earth” in worldspace.

In coordsys world

(

asteroid1.transform = my_matrix * earth.transform

)

In 3DS Max, that would snap "asteroid1" to where "moon" was relative to the
"earth". As a bonus, I'd love the option of being able to snap ONLY
"asteroid1"'s translation OR ONLY it's rotation if I so choose.

I've tried using maya's xform and getAttr commands. I've also tried some
OpenMaya commands suggested by a friend, like .MTransformationMatrix(), and
.asMatrixInverse(), but I don't have enough experience to know how to get
the result I'm looking for. Usually it comes down to me not knowing how to
"multiply" the matrix * the child object's transform node. I'm eager to
learn how to use the MfnTransform and inclusiveMatrix, but I don't have a
good jumping off point. The simpler solution the better for me.

Any advice would be appreciated!

Thanks

Yep, I think the better and faster way it's MfnTransform and
inclusiveMatrix :)
--------------------------------
Marco D'Ambros
phone : [phone]

You can get matrices with MDagPath::inclusiveMatrix or exclusiveMatrix.
To set a matrix, you can use MFnTransform. The MPx* classes are proxy
classes that you only use when creating a custom object like a node or
context.
Chad

Hi all,
i have a script that calculates per vertex tangent space and constructs
a matrix. which all works fine but now i'm just looking at trying to get it
to work in a global position.
what is the best way in Api to get the objects Inverse Square matrix or
an object? there seems to be a few options whats the deference
any guidance would be great
john
--
http://groups.google.com/group/python_inside_maya

--
http://groups.google.com/group/python_inside_maya

[Marcus Ottosson]

Sounds like you’ve got a number of problems here and I’m not sure which
ones solves your problem, but I might be able to help you with this.

Usually it comes down to me not knowing how to “multiply” the matrix * the
child object’s transform node

In Maya, there’s an output on each transform node that carries it’s matrix;
it’s called simply matrix. It’s also got inverseMatrix and worldMatrix
which are self-explanatory. You can multiply these with a multMatrix
<http://help.autodesk.com/cloudhelp/2015/ENU/Maya-Tech-Docs/Nodes/multMatrix.html>
node, that you can create and connect like so:

from maya import cmds

multMatrix = cmds.createNode("multMatrix")
# Connect to multMatrix
cmds.connectAttr("moon.worldMatrix", multMatrix + ".matrixIn[0]")
cmds.connectAttr("earth.worldMatrix", multMatrix + ".matrixIn[1]")

At this point, multMatrix will contain the multiplied matrix.

print cmds.getAttr(multMatrix + ".matrixSum")# [1.0, 0.0, 0.0, 0.0,
0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0]

You can convert the matrix back to translation values using decomposeMatrix,
so that you can hook it back up to whichever node you are looking to drive.

As for saving it out, you can export the multMatrix node and import it back
in, it will still contain the values, although ideally you’d simply make it
procedural and maintain the connections. But I must admit I’m not fully
understanding what you’re trying to accomplish. Maybe if you break it down
into one question at a time, we could get a little closer to a solution.

Best,
Marcus
​

Post by V126
Hey guys,
I'm a noob, and am trying to understand how to use the inverse matrix
better. It's related to this thread so I'm replying here. I've searched
through all the documentation and posts and haven't found an answer (that I
can fully comprehend) yet.
My previous experience comes from maxscript, so I'll have to use it as
pseudocode to illustrate.
I've got three objects with transform nodes: "moon", "earth" and
"asteroid1". I want to save the translation and rotation of "moon" relative
to "earth" into a variable, so I can snap "asteroid1" to that exact
translation and rotation that the moon has, relative to the "earth". I want
to save it in a variable so I can use that relative position and rotation
in another file that doesn't have the "moon" in it (therefore I can't cheat
and just xform "asteroid1" to "moon").
# Get a transformation matrix of the “moon” to the “earth”.
my_matrix = moon.transform * inverse earth.transform
# Then use that matrix to snap the “asteroid1” to the location I recorded
relative to the “earth” in worldspace.
In coordsys world
(
asteroid1.transform = my_matrix * earth.transform
)
In 3DS Max, that would snap "asteroid1" to where "moon" was relative to
the "earth". As a bonus, I'd love the option of being able to snap ONLY
"asteroid1"'s translation OR ONLY it's rotation if I so choose.
I've tried using maya's xform and getAttr commands. I've also tried some
OpenMaya commands suggested by a friend, like .MTransformationMatrix(), and
.asMatrixInverse(), but I don't have enough experience to know how to get
the result I'm looking for. Usually it comes down to me not knowing how to
"multiply" the matrix * the child object's transform node. I'm eager to
learn how to use the MfnTransform and inclusiveMatrix, but I don't have a
good jumping off point. The simpler solution the better for me.
Any advice would be appreciated!
Thanks

Yep, I think the better and faster way it's MfnTransform and
inclusiveMatrix :)
--------------------------------
Marco D'Ambros
phone : [phone]

You can get matrices with MDagPath::inclusiveMatrix or exclusiveMatrix.
To set a matrix, you can use MFnTransform. The MPx* classes are proxy
classes that you only use when creating a custom object like a node or
context.
Chad

Hi all,
i have a script that calculates per vertex tangent space and constructs
a matrix. which all works fine but now i'm just looking at trying to get it
to work in a global position.
what is the best way in Api to get the objects Inverse Square matrix or
an object? there seems to be a few options whats the deference
any guidance would be great
john
--
http://groups.google.com/group/python_inside_maya

--
http://groups.google.com/group/python_inside_maya

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