CompuServe Messages

We are using the 3D Studio Release 3 File Toolkit to read in mesh and keyframe info. Our model is rotating a small amount around the axis <1,0,0>. We figured out that while the translations are absolute, the rotations are incremental. Sometimes the axis is <1,0,0> and sometimes it is <-1,0,0>, but the sign of the angle is not inverting. This is causing our animated model suddenly change heading by 90 degrees. Is this in some way related to quaternions? To build a cumulative rotation matrix for each keyframe, I first construct a quaternion from the axis and angle, construct a rotation matrix from the quaternion, then concatenate it with the previous rotation matrices. Is this a correct procedure given the format of the rotation keyframes, or am I neglecting an important piece of data? Thanks, Mark Hodges Gravity Inc.