Synopsis
		sfdistance < points.rsf > dist.rsf velocity=vel.rsf n1= n2= n3=1 d1= d2= d3=d2 o1=0. o2=0. o3=0. order=2 vel=y

Parameters
		float d1=   float d2=   float d3=d2 sampling   int n1=   int n2=   int n3=1 dimensions   float o1=0.   float o2=0.   float o3=0. origin   int order=2 [1,2] Accuracy order   bool vel=y [y/n] if y, the input is velocity; n, slowness squared   string velocity= auxiliary input file name