You will just have to decide how many pixels will make up a kilometer then calculate a scaleing factor...
example:
5 pixels per meter
then to calculate Vspeed and Hspeed:
example:
5 pixels per meter
pixels_per_meter# = 5 scale_factor# = pixels_per_meter# / 1000
then to calculate Vspeed and Hspeed:
Vspeed# = (speed * scale_factor#) * SIN(angle) Hspeed# = (speed * scale_factor#) * COS(angle)