D99 atlas coordinate

In the D99 template what is the origin of the DV coordinate? In the original atlas DV was with respect to interaural but looks like in the digital version it is with respect to anterior commissure. The same seems true for AP. would you please clarify?

It has the (0,0,0) coordinate set explicitly at the AC center. The whereami interface provides a simple affine transformation to produce the coordinate in the D99_Book space where the (0,0,0) is based on the earbar-zero position.