Synopsis
		sftrace2 < vel.rsf > outp.rsf size=size.rsf grid=grid.rsf na=60 da=3.1 a0=-90. maxsplit=10 minx=0.5*dx maxx=2.*dx mina=0.5*da maxa=2.*da vel=y order=3

Parameters
		float a0=-90. initial angle (in degrees)   float da=3.1 angle increment (in degrees)   file grid= auxiliary output file name   float maxa=2.*da   int maxsplit=10 maximum splitting for adaptive grid   float maxx=2.*dx   float mina=0.5*da   float minx=0.5*dx parameters for adaptive grid   int na=60 number of angles   int order=3 velocity interpolation order   file size= auxiliary output file name   bool vel=y [y/n] y: velocity, n: slowness