Program sfztrace | Multiple arrivals by depth marching. 
[SYNOPSIS]
sfztrace < in.rsf nt=nx*nz na=362 da=0.5 a0=-90. vel=y order=3 iorder=4
[PARAMETERS]
float   | a0 | =-90. |   | 	starting angle (in degrees) 
float   | da | =0.5 |   | 	angle increment (in degrees) 
int     | iorder | =4 |   | 	interpolation accuracy for grid 
int     | na | =362 |   | 	number of angles 
int     | nt | =nx*nz |   | 	ray length bound 
int     | order | =3 |   | 	interpolation accuracy for velocity 
bool    | vel | =y |  [y/n] | 	y, input is velocity; n, slowness 
[DIRECTORY]
user/fomels
