Synopsis
		sfpickvert < scn.rsf > pik.rsf vel0=o2 niter=100 an=1. gate=3 smooth=y eps=1e-6 rect#=(1,1,...) rect1=1 rect2=1 ...

rectN defines the size of the smoothing stencil in N-th dimension.

Theory in Appendix B of:
S. Fomel, 2009,
Velocity analysis using AB semblance: Geophysical Prospecting, v. 57, 311-321.
Reproducible version in RSFSRC/book/jsg/avo

Parameters
		float an=1. axes anisotropy   float eps=1e-6 verticality measure   int gate=3 picking gate   int niter=100 number of iterations   int rect#=(1,1,...) smoothing radius on #-th axis   bool smooth=y [y/n] if apply smoothing   float vel0=o2 surface velocity