The directional scanner creates a cone x degrees wide and y meters in length. This cone points in the same direction as the "camera" in eve. You can have the scanner use your active overview settings or use the default list of items to display.
The directional scanner is used to detect enemy players or POS locations. It can also be used to detect bubbles on gates. The directional scanner does not detect wormholes or exploration sites.
Here is how I scan down ratters.
1) Hold cloak on the gate
2) Do a 360 degree/max range scan to see if there is anything in range
3) Hit F11 to get a quick idea of the layout of the solar system
4) Do a 180 degree/max range scan if there are multiple belts around me to see what side the target is on.
5) Do a 90 or 60 degree/max range scan to narrow the hit down to a planet.
6) Warp to a random belt of the target planet.
7) While in warp do 15 degree scans and vary the range if needed to locate the target's belt.
8) If my random guess was wrong, warp to the correct belt.
A good player can pick a belt and be in warp within 30 seconds. If the ratter is slow you can generally catch them.
The other use for the scanner is detecting hostile gate camps. I will setup scan points (bookmarks) near gates and warp there first when there are reds in system. I then do a narrow scan with the camera "pointed" at the gate. I have an overview setting that will show bubbles, jetcans, and ships which I select while scanning. If there is a bubble at the gate and a bunch of hostiles I go somewhere else. If there is a bubble and no hostiles I'll warp in @ 100km, get sucked into the bubble, bookmark that spot, turn around and exit the bubble and warp back to my scan point. Then I can warp to that bookmark @ 100km without getting sucked into the bubble. You don't necessarily need to point the scanner to do this. By varying the range you can usually make a 360 degree scan overlap just the gate you want. It is not as accurate of a picture but is suffices for hostile detection.
The way I see it you would need the following minimum features:
1) A method to start a 360 degree scan with a variable range. This method should return an index of scan results. These aren't entities at this point because you can't warp to them. Unless that is just hidden by the client which would make an uber hack possible. :evil:
2) A method to set the active overview setting.
I hope that all was coherent.