# trasformation matrix for model's bones

I was developing an fbx converter for legend of grimrock object model (www.grimrock.net), I just wanted to get the animations cause the rest has been converted by others' tools. I was reading all of their guidelines to convert from their little endian binary file to the format I want (in this case fbx) When I was about to construct the skeleton, I was stuck because of this

// A Mat4x3 is a transformation matrix split into 3x3 rotation and 3D rotation parts
struct Mat4x3
{
Vec3    baseX;
Vec3    baseY;
Vec3    baseZ;
Vec3    translation;
}


(btw Vec3 is a three dimensional vector (xyz) you can find complete specifications of their object model here)

what does "A Mat4x3 is a transformation matrix split into 3x3 rotation and 3D rotation parts" mean???? Regarding the creation of bones, I thoughtmatrix should be a transformation matrix not a rotation matrix. So I'm kinda confused. Anyway I should calculate this way? (o = origin)

x' = x*x1 + y*y1 + z*z1 + o1;
y' = x*x2 + y*y2 + z*z2 + o2;
z' = x*x3 + y*y3 + z*z3 + o3;

• Why not asking them what they mean by it? – Trilarion Oct 24 '14 at 12:53
• Well they simply didn't give any help and they didn't answer. Private messages on the forum to the developers is not permitted.. I'm getting crazy lol – kaomao Oct 24 '14 at 12:54

## 1 Answer

If you have conflicting comments and code, either one or both of them are incorrect.

In this case, it seems likely that the 3D rotation in the comment is supposed to be a 3D translation.

In general, a 4x3 transformation matrix is like a regular 4x4 transformation matrix, but the fourth part with [0 0 0 1] is omitted for saving space and work.

• thank you!!! unfortunately I'm not so great at linear algebra so I'm finding a way to get this sorted out, that comment was misleading I guess. – kaomao Oct 24 '14 at 15:01