Synopsis
		sfvelsteer < in.rsf > out.rsf nvx= dvx= ovx= nvy= dvy= ovy= iypi=0 iyps=ny-1 xp=

Parameters
		float dvx= vx sampling   float dvy= vy sampling   int iypi=0 first depth position where velocity steering is computed   int iyps=ny-1 last depth position where velocity steering is computed   int nvx= number of vx values   int nvy= number of vy values   float ovx= vx origin   float ovy= vy origin   float xp= lateral position where velocity steering is computed