W3C home > Mailing lists > Public > public-geolocation@w3.org > April 2010

Re: Orientation event draft

From: Steve Block <steveblock@google.com>
Date: Wed, 21 Apr 2010 09:32:14 -0700
Message-ID: <z2sb39f53b21004210932yb18e9c49u27bbeade6e7f518c@mail.gmail.com>
To: public-geolocation <public-geolocation@w3.org>
Thanks for the comments.

> I don't like attribute names theta, phi and gamma.
> Could we have something more describing.
Do you have any suggestions? One possibility is roll, pitch and yaw,
as used in aviation. However, this is potentially confusing, as in
aviation, the x axis (about which roll is performed) runs along the
long axis of the body, whereas here the A axis is perpendicular to

> "Implementations that are unable to provide all three angles must set the values of the unknown
> angles to null"
> That is strange. The type of the property is double. That kind of properties don't usually give
> suddenly non-numeric values.
There is precedent for this in the Geolocation spec.

> The draft doesn't say what is the type of the dispatched AccelerometerEvent.
Correct, now fixed.

> The angles are described in relation to the device axes (A, B, C), not the local reference frame
> (X, Y, Z), which doesn't help in making this any clearer.  There is no clear link between (A, B, C)
> and (X, Y, Z).
The three rotation angles describe exactly the transformation to move
from the Earth frame XYZ to the body frame ABC.

> Would I be right in assuming that 0, 0, 0 orientation equates to a device with the screen facing
> up and the top of the screen toward north?

> Could you also describe rotation a little more clearly.  Clockwise when viewed along an axis isn't
> sufficiently clear.  From the examples, I would assume that this is when values on the axis
> increase in the direction the viewer is facing.
Correct. The spec says 'Positive rotation around an axis is defined as
clockwise when viewed along the positive direction of the axis.'

> I'd also point that the choice of rotation direction is a difficult one that needs more explanation.
> Most people are accustomed to having East at 90 degrees (even if that is counter to
> mathematical convention.
Sure, I've added a note.

> Could a diagram (or diagrams) be added?
Yes, I've added some (quick and dirty!) graphics. Let me know if they
help to clarify the rotations.


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Received on Wednesday, 21 April 2010 16:32:46 UTC

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