TETRAMOD - TETRAhedron MODel builder. In each layer, velocity gradient       is constant or a 2-D grid; horizons could be a uniform grid and/or       added by a 2-D grid specified.   				 tetramod [parameters] > tetrafile		 			 Required parameters:							 nxhz=		number of samples (2nd dimension) for horizons		 nyhz=		number of samples (1st dimension) for horizons		 hzfile=	output xhz,yhz,zhz,v0hz,v1hz for viewer3                 Optional parameters:							 xmin=0       	x of the lower left point in the model	        	 ymin=0        y of the lower left point in the model                   xmax=2        x of the upper right point in the model                  ymax=2        y of the upper right point in the model                  zmax=(max z)  max z in the model                                       blt=1.0       bottom layer thickness                                   nhz=1		number of layers in the model (except the model base)	 ficth=-1      ficticious horizons (no velocity interpolation based on them) The following four numbers define the four corners for 3-D model;	 z00=0,0.6,1.2,... 	z at (xmin,ymin) on each horizon		 z01=0,0.6,1.2,... 	z at (xmin,ymax) on each horizon		 z10=0,0.6,1.2,... 	z at (xmax,ymin) on each horizon                 z11=0,0.6,1.2,... 	z at (xmax,ymax) on each horizon                 v00=1.0,2.0,3.0,...	v at (xmin,ymin) on each horizon		 v01=1.0,2.0,3.0,...	v at (xmin,ymax) on each horizon		 v10=1.0,2.0,3.0,...	v at (xmax,xmin) on each horizon                 v11=1.0,2.0,3.0,...	v at (xmax,xmax) on each horizon                 dvdz00=0,0,0,...   	dvdz at (xmin,ymin) on each horizon		 dvdz01=0,0,0,...   	dvdz at (xmin,ymax) on each horizon		 dvdz10=0,0,0,...   	dvdz at (xmax,xmin) on each horizon              dvdz11=0,0,0,...   	dvdz at (xmax,xmax) on each horizon              x0file=   	x grid for horizon 0 					 y0file=   	y grid for horizon 0 					 z0file=	z grid for horizon 0 added to 4-z interpolation   	 v0file=	v grid for horizon 0 added to 4-v interpolation   	 dvdz0file=	dvdz grid for horizon 00 added to 4-dvdz interpolation	 x1file=	x grid for horizon 1					 y1file=	y grid for horizon 1					 z1file=	z grid for horizon 1 added to 4-z interpolation  	 v1file=	v grid for horizon 1 added to 4-v interpolation  	 dvdz1file=	dvdz grid for horizon 1 added to 4-dvdz interpolation	 ...		for horizon  #2, #3 #4, etc... 				 verbose=0	=1 print some useful iinformation			 Remarks:								 TETRAMOD defines its own grammar to describe a 3-D model (including a  tetra file for ray tracer SUTETRARAY and a horizon file for VIEWER3    Disclaimer:                                                            This is a research code that will take considerable work to get into   the form of a a production level 3D migration code. The code is        offered as is, along with tetramod and sukdmig3d, to provide a starting point for researchers who wish to write their own 3D migration codes. Credits:  	CWP: Zhaobo Meng, 1996  Reference:  Zhaobo Meng and Norman Bleistein, Wavefront Construction (WF) Ray "Tracing in Tetrahedral Models -- Application to 3-D traveltime and  ray path computations, CWP report 251, 1997