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Be clear that sensor frames include data at two instants, not two different IMUs #10

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m-7761 opened this issue Jun 22, 2018 · 3 comments
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@m-7761
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m-7761 commented Jun 22, 2018

Just for what it's worth, I've been working with the PSVR for a while, going on what is available on the WWW. The way there are 2 sets of figures in the USB data, for the sensors, gave me the impression that there was actually 2 sets of sensors inside there.

It may sound dumb, but I think it's worth including explicit notes wherever the USB structured data is displayed, that they are two samples, packed together for USB protocol reasons. Thanks!

@m-7761
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m-7761 commented Jun 22, 2018

Is "dumb blonde" still socially acceptable? In any case, from...

https://github.com/gusmanb/PSVRFramework/wiki/Report---Sensor-Data

Gyroscope 2

    36: short, Yaw (signed, +ve turn left, -ve turn right)
    38: short, Pitch (signed, +ve look up, -ve look down)
    40: short, Roll (signed, +ve clockwise, -ve anticlock)

Accelerometer 2

    42: short, X axis //Corrected
    44: short, Y axis //Corrected
    46: short, Z axis //Corrected
    47: byte, Unknown

Try to avoid calling things "Gyroscope 2" and "Accelerometer 2" since that strongly gives the impression that there are in fact two of each. Still, even without reading "2" I don't know if I would've automatically assumed that these are samples instead of two sensor housings with independent internal clocks.

@dylanmckay
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Our documentation contains this comment.

I also want to write a little bit more about it once the question in #2 is answered.

  // Two readouts from the BMI055 IMU at different time instants.
  //
  // The integer values within are between -32768 and 32767, i.e.
  // they can take the entire range of a 16-bit signed int.
  //
  // These values can be converted to [-1.0, +1.0] floats by
  // casting to float and simply dividing by 32768.
  //
  // FIXME: Find out the time delta between these two measurements,
  //        document it.

@dylanmckay dylanmckay changed the title 2 samples per USB datagram, or 2 sets of sensors? Be clear that sensor frames include data at two instants, not two different IMUs Jun 30, 2018
@m-7761
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m-7761 commented Jul 1, 2018

That is good, but I'm not sure // comments are ideal, because I did look over this page once, and that did not stand out to me at the time. I would change "different" to subsequent.

EDITED: I also, strongly advise to use the word "sample" because developers understand that word instinctively I believe. "Two samples" would be a stronger lead, whereas "readout" is ambiguous, until the end of the statement.

@dylanmckay dylanmckay self-assigned this Jul 10, 2018
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