Introduction - If you have any usage issues, please Google them yourself
AVSPOS extracts the available satellite position (XYZ)
XYZ=avspos(X,Y,P1,P2) extracts the visible satellites, which are described
in P2, from the matrix X. The output XYZ is a N-by-3*M matrix with the
coordinates of the visible satellites.
The Matrix Y just tells us if the satellites are visible at every epoch and
which not. P1 is a vector of all satellites.