Calculate strike and dip from euler angles given by Javascript deviceOrientation API

The w3c specs http://ift.tt/1i2JXXi give us the necessary documenation to access the get the euler angles of a device orienation and its conversion to the direction cosine matrix, my question is about calculating the

DIP:the acute angle that a rock surface makes with a horizontal plane and STRIKE: is the direction of the line formed by the intersection of a rock surface with a horizontal plane

from the Euler angles, for any arbitrary orientation of the phone or device on a plane. strike can be done with the compass-heading + 180deg but the dip implementation is something confusing P.S. any code/algorithm explanation will suffice. thank you