how to get vector plots and contour lines in OpenGL

Hello there,

I have following four column data with me..

Latitude, Longitude, U (velocity along x) and V (velocity along y)

Now using these data, I got to display vector plots where the velocities u and v are shown using arrows..

I am able to get the magnitude to be displayed... Now the problem is that i am not able to show the direction.. ( direction in terms of arrow) In other words how do i display an arrow at the head part of that vector.??

Second thing is that i have another set of data

Latitude, Longitude, and Depth..

Using these data, i need to display line contours.. Any slight initiation to solve this problem will be grateful...

Thanks in advance