Seyren Windsor - 1 month ago 11

Python Question

I'm working to import transformation from a left coordinate system (unity/maya) to 3ds max, which is right handed from a file.

3ds Max uses a 3x4 matrix, but it's the same as a 4x4 matrix but with the last column removed (which does not really do anything so no data is lost)

The translation in the matrix is kind of easy, since i just have to swap the last row from [x y z] to [-x z y] when getting the original matrix, swapping the y value for the z value and setting the x to negative.

Is not as easy for the rotation though.

I kind of tried to do a workaround, by getting the quaternion of the matrix, changing it to euler, doing the same swap as stated previously and putting it as a quaternion again, and the rotation comes a bit off.

I was wondering if there is a sequence of matrix operations that can be done to the original matrix to make it ready to set for right-handed 3ds max coordinates, since the initial ones are left-handed.

I saw in some docs to set the z value as negative, but that did not really work.

Is there any good documentation about this or any place i can follow? every doc i look has different solutions and this begins to be confusing.

Answer

I fixed this by doing the following:

- Import the scene/models the way it is.
- If there isn't a root, create it and link all objects that don't have a parent to the root created.
- Rotate the root to apply that transform to everything until you have the desired result.

If you are in 3ds Max, you can go to the maxscript listener and type: "$.transform". This will give you the transform of the object you are currently selecting, so select the root and write it on the console and you will get a transformation matrix that you need to apply.

Now, you can either save this matrix on a file and apply it, or if you want to be more precise, everytime you are going to work with it, do the third step from above in a script to a dummy object and then you can just multiply it to any object in the scene. For example:

```
root = Dummy()
root.rotation = (quat 0 -0.707107 0.707107 0)
root.scale = Point3 -1 -1 -1
```

Every coordinate system is it's own thing, so you'll get different values. Now you just have to do the following to any object:

```
object.transform *= root.transform
```

That will give you the proper transform you need.