SUMIGFD - 45-90 degree Finite difference migration for zero-offset data.

sumigfd <infile >outfile vfile= [optional parameters]

Required Parameters:
nz= number of depth sapmles
dz= depth sampling interval
vfile= name of file containing velocities
(see Notes below concerning format of this file)

Optional Parameters:
dt=from header(dt) or .004 time sampling interval
dx=from header(d2) or 1.0 midpoint sampling interval
dip=45,65,79,80,87,89,90 Maximum angle of dip reflector

tmpdir= if non-empty, use the value as a directory path
prefix for storing temporary files; else if the
the CWP_TMPDIR environment variable is set use
its value for the path; else use tmpfile()

Notes: ",
The computation cost by dip angle is 45=65=79<80<87<89<90

The structure of input velocity file is vfile[iz][ix]. Note that the
x-direction is the fastest direction instead of z-direction! Such a
structure is more convenient for the downward continuation type
migration algorithm than the usual z as fastest dimension encountered
in other SU programs.

Because most of the velocity file is in vfile[ix][iz] structure, you
can use \'transp\' in SU to transpose them into vfile[iz][ix] structure.



Credits: CWP Baoniu Han, April 20th, 1998

Trace header fields accessed: ns, dt, delrt, d2
Trace header fields modified: ns, dt, delrt