function tspvd(cdf,sta,lev)
[u,v,t]=velts(cdf,sta,lev);
dt=t(2)-t(1);   % time interval in seconds
[x,y]=pvd(dt/1.e3,u,v);   % (s * km/m) * m/s
w=x+i*y;
polar(angle(w),abs(w));
xlabel('km')
ylabel('km')
title('progressive vector diagram')
