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Old Jan 26th 2011, 01:11 PM   #1
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Join Date: Jan 2011
Posts: 4
Position/Motion Vector Getting a future position


I am currently reading a paper where itís necessary to know the position of a node at a future time. A node will know its current (x,y) position, its previous (x,y) position one second ago and will know its current speed.

The paper says the following:
v(I,T): motion vector of a node I at time T
p(I,T): position vector of node I at time T
It gives the following relationship:
p(I,Tc)=p(I,Tr) + v(I,Tr).(Tc-Tr) where Tr is a past time, Tc is the current time
(This is basically the distance=speed*time formula from what I can see with the distance added to the (x,y) coordinates).

Part of the algorithm says that a node should predict the position of another node at time Tc + Δt, where Δt is a small time like 1s, if it knows the nodes current position and motion vector. It says it relies on the accuracy of the motion vector and then says the following:
Let m denote the motion vector directly accessed from GPS. Mold and Mnew are the reported motion vectors at the last time and this time respectively.
Mnew = alpha*Mold + (1 Ė alpha)*m, 0<=alpha<=1
Alpha=0.3 if the node is in the area of a junction, 0.7 otherwise
I am a programmer and donít understand fully what information I should actually store in the motion vector and still donít understand how given a nodeís (x,y) position and speed at time Tc, I can work out its position at time Tc + 1 given that it could have moved in any direction?

Can somebody please outline as simply as possible how I can get this future value?

I am quite stuck so any help appreciated.

Many thanks in advance.

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future, position, position or motion, vector

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