Greetings,

We recently ran into some behavior that we don’t quite understand whenever lights or cameras are exported.

In a simple Max scene consisting of a free camera, target direct light, and a mesh, the camera and light have an additional post rotation applied. For the camera, the postrotation is (0,-90,0). For the light, it is (-90,0,0). This also being exported with Z-up.

The closest answer that I could find was here:

http://area.autodesk.com/forum/autodesk-fbx/fbx-sdk/max-cameras-and-postrotation/

But I’m still not entirely clear why the rotation needs to be applied. That link doesn’t also really explain why lights need it, too.

If anyone could elaborate on this or point me towards any additional resources, I’d appreciate it. I didn’t really find anything talking about this specifically in the SDK docs (though I could’ve missed it).

Thanks

Investigating further, it seems as though that I’m getting bogus rotations for cameras and lights.

Taking a target direct light as an example. In Max 2010, I have it located at (-0.696, 104.816, 0.0) in the world with euler rotations of (-90, -180, 0.155). In maxscript, I dumped out the transform:

$Direct01.transform
(matrix3 [-0.999996,-0.00270572,0] [0,0,1] [-0.00270572,0.999996,0] [-0.696054,104.816,2.0249e-006])

So far, this seems correct. When I export to FBX (2012) with z-up, the FBX file has this entry:

Model: 791804896, “Model::Direct01”, “Light” {
Version: 232
Properties70:  {
P: “PostRotation”, “Vector3D”, “Vector”, “”,-90,-0,0
P: “RotationActive”, “bool”, “”, “”,1
P: “InheritType”, “enum”, “”, “”,1
P: “ScalingMax”, “Vector3D”, “Vector”, “”,0,0,0
P: “DefaultAttributeIndex”, “int”, “Integer”, “”,0
P: “Lcl Translation”, “Lcl Translation”, “”, “A”,-0.696053683757782,104.815559387207,2.02489763978519e-006
P: “Lcl Rotation”, “Lcl Rotation”, “”, “A”,89.9999993235163,-0,-179.844973597
P: “Lcl Scaling”, “Lcl Scaling”, “”, “A”,1.00000002457802,1,1.00000002457802
P: “MaxHandle”, “int”, “Integer”, “UH”,2
}
MultiLayer: 0
MultiTake: 0
Shading: T
Culling: “CullingOff”

The first thing that I noticed is that the local rotation and post rotation are not what I expected. Even when I manually calculate LclRotation*PostRotation, I get

- 0.9999963 1.223D-16 0.0027053
1.223D-16 1.  - 3.311D-19
- 0.0027053 - 2.241D-22 - 0.9999963

Finally, I opened the FBX file in the “Transformation” example that comes with the SDK. It seems to complain about the camera, too.

Direct01
Error: The two global transform results are not equal!
KFbxEvaluatorGlobalTransform Row_0: -0.999996, -0.002706, 0.000000, 0.000000
KFbxEvaluatorGlobalTransform Row_1: -0.002706, 0.999996, 0.000000, 0.000000
KFbxEvaluatorGlobalTransform Row_2: -0.000000, 0.000000, -1.000000, 0.000000
KFbxEvaluatorGlobalTransform Row_3: -0.696054, 104.815559, 0.000002, 1.000000

FromScratchGlobalTransform Row_0: -0.999996, -0.002706, 0.000000, 0.000000
FromScratchGlobalTransform Row_1: 0.002706, -0.999996, -0.000000, 0.000000
FromScratchGlobalTransform Row_2: 0.000000, -0.000000, 1.000000, 0.000000
FromScratchGlobalTransform Row_3: -0.696054, 104.815559, 0.000002, 1.000000

So far, neither the evaluator or “scratch” global transforms match what I get when I dump the transform info with maxscript.

At this point, I’m a little lost as to what’s going on. I’ve seen similar behavior when I look at a camera node. If anyone has any insight, I would certainly appreciate it!

(I also attached the FBX file that I’ve been using)

Thanks.