sparPositionType, a sparPostion defines a location within the componentSegment where a spar in mounted. Eta and xsi are relative to the componentSegment.

Please find below a picture for an example definition of 3 spars in one wing, by using spar position points and spar segments:

As an alternative to the relative eta coordinate it is possible to specify an elementUID so that the spar position is relative to the outer geometry, e.g. kink, of the wing.