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 input velocity file \'vfile\' consists of C-style binary floats.	", 
 The structure of this file is vfile[iz][ix]. Note that this means 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 using z as fastest dimension as in other SU	
 programs.							
 
 Because most of the tools in the SU package (such as  unif2, unisam2,	
 and makevel) produce output with the structure vfile[ix][iz], you will
 need to transpose the velocity files created by these programs. You may
 use the SU program \'transp\' in SU to transpose such files into the	
 required 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