where/how is the fixed key-frame/reference handled in MSF?

[protobits]

The IROS2013 paper specifices how relative updates are handled for pose estimates coming from SLAM. However, I can't find where/how this is handled in the code. I was expecting ptam to publish the pose of the reference (fixed) key-frame as well as the current pose, however I did not find that either.

Actually, what I can only find is that a measurement can be considered relative to last one, but this would not be desireable, exactly as the paper states. Instead, I was expecting this same logic to be performed w.r.t. to a fixed keyframe. Is that not implemented?