Oh... OK, if a parrallel LOB is possible, that means you're also plotting or inputting an (x,y) position as the point of origin for the LOB. I do see now that you did mention that in your post... and you input an obs time too.
You're taking the DRT (dead reckoning tracker) approach. The benefit to the DRT method is that you don't have to maintain your own course and speed. The downside is you have to track your own position.
How are you entering/determining the position data? I haven't played my copy of DW much since I bought it... I assume it must provide you with a readout showing your position, and that's what you're using for an input?
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