Velocity of moving object at x and y axis

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BlueBee77 2017-4-6

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评论： BlueBee77 2017-4-6

I want to calculate the velocity and acceleration of a moving object. I have the centroid value and i am calculating the distance covered by using euclidean distance formula on current and previous centroid. I am confused on how do we calculate velocity and acceleration of a moving object at x and y-axis. Do we simply divide the euclidean distance formula into x(centroid x) and y(centroid y) parts?

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KSSV 2017-4-6

Velocity is defined as displacement over time. You have distance now, do you have time?

BlueBee77 2017-4-6

Yes, i have displacement and time. Just confused on how to get velocity x and velocity y

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Answer 1

Jan 2017-4-6

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编辑：Jan 2017-4-6

在 MATLAB Online 中打开

You can get the velocities in X and Y direction independently.

Vx = gradient(X, TimeStep);
Vy = gradient(Y, TimeStep);

Or:

S = blobCentroid - PrevCent;
V = gradient(S, TimeStep);

Now V contains teh X and Y component.

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Jan 2017-4-6

在 MATLAB Online 中打开

@BlueBee77: Start with defining, what you want to know: If you want the velocities in X and Y direction separately, you do not need the Euclidean distance. If you want the total velocity independent from the direction, the Euclidean distance will solve this. Or you can calculate the velocities in X and Y direction at first, and then V_total = sqrt(V_x ^ 2 + V_y ^ 2).

It might get clear with an example: The object travels from the point (1, 2) to (2, 4) in 1 time unit h (e.g. seconds, but we can omit the units here). Then:

V_x = (2 - 1) / h = 1
V_y = (4 - 2) / h = 2
V_total = sqrt(1^2 + 2^2) = 2.236

Or you use the Euclidean distance:

V_total = Dist / h = sqrt((2 - 1)^2 + (4 - 2)^2) / h = 2.236

Both calculations are equivalent. In fact, the same numbers appear in the same equations.

BlueBee77 2017-4-6

@Jan Simon: Thanks alot for such a nice explanation and solving my problem. I need the velocities and acceleration in X and Y direction :)

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Answer 2

Image Analyst 2017-4-6

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You can use diff(distances) to get "instantaneous" velocity. Then again on velocity to get acceleration. Or use diff(x) and diff(y) to get velocity components along the two directions separately.