Show HN: Visualizing the math that powers 3D character animation

Re:Show HN: Visualizing the math that powers 3D character an... by saeranv on Monday June 13, 2022 @06:02PM (#31732348)

I'm a little confused about why the curves are "sampled" to update the joint transformations: ``` So if we are rendering 60 frames per second, we are basically doing the following 60 times a second:

Sample all the curves you see on the graphs to get the orientation of each joint... ```

When the curves are "sampled", does that mean in a 60 fps animation, there are 60 timestep values t={t1, t2, ... t60} sampled from a uniform distributions, and evaluated at x(t), y(t), z(t), and w(t), and then those values are stepped through sequentially? If that is the case, why not just set t={1/60, 2/60, ... 1}?

Or does "sampling" here just mean function is evaluated at an appropriate t value, and not refering to statistical sampling?

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Re:Show HN: Visualizing the math that powers 3D character an... by danachow on Monday June 13, 2022 @06:09PM (#31732411)

https://en.wikipedia.org/wiki/Sampling_(signal_processing)

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Re:Show HN: Visualizing the math that powers 3D character an... by saeranv on Tuesday June 14, 2022 @11:35AM (#31741023)

This definition clears up it up nicely for me:

"In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal... A sample is a value of the signal at a point in time and/or space; this definition differs from the usage in statistics, which refers to a set of such values."

So it's a sample in the sense a set of (x, y, z, w) values from discrete timesteps represents a continuous timestep, but doesn't require specifying and using random variables to determine those timesteps.

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Re:Show HN: Visualizing the math that powers 3D character an... by jameshart on Monday June 13, 2022 @07:18PM (#31732933)

Yes, sampling means ‘reading the value at a particular time’. Same sense as in signal processing.

If everything goes to plan, you are sampling at 1/60, 2/60, etc.

But if the previous frame took a bit longer to render, you might be at a different time. What you want is the value for all of those curves at whatever time it is, not at some fixed time.

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Re:Show HN: Visualizing the math that powers 3D character an... by diegomacario on Tuesday June 14, 2022 @08:19AM (#31738095)

Sorry for the confusion. Your second statement is correct. Sampling just means to evaluate the function at an appropriate t value. I will update the README to make this clearer.

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Re:Show HN: Visualizing the math that powers 3D character an... by arjvik on Monday June 13, 2022 @06:08PM (#31732405)

Pretty sure it just means evaluated at a finite number of appropriate t values and interpolated to find intermediate values.

I agree that it's definitely an abuse of terminology.

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