W3C home > Mailing lists > Public > public-geolocation@w3.org > May 2011

Re: axes and normalization of orientation events

From: Steve Block <steveblock@google.com>
Date: Mon, 16 May 2011 16:16:54 +0100
Message-ID: <BANLkTi=zB4AVzDhDF+eHhnmGi2QoqEFZCw@mail.gmail.com>
To: Dean Jackson <dino@apple.com>
Cc: public-geolocation@w3.org
Hi Dean,

> However, in researching it I notice that the W3C spec lists the axes in a different order than the convention used by
> the rest of the world.
I'm aware that in vehicle dynamics the x axis usually points in the
direction of motion, but do you have a reference for a standard for
non-vehicle applications, like a UA? We chose the Earth frame to be
East-North-Up and it made sense to align the body frame such that it
matches the Earth frame when viewing a map on the device, though I
don't feel strongly about this.

> Also, I notice that the spec says "Rotations use the right-hand convention: positive rotation around an axis is
> clockwise when viewed along the positive direction of the axis". It's highly likely that I'm misinterpreting this, but a
> rotation around Z using the right hand rule (from X axis to Y axis) is counter-clockwise. In fact, the little arrow on the
> diagram shows this.
Yes, I think you're misinterpreting this. Talking about clockwise vs
counter-clockwise only makes sense when you specify the direction the
observer is facing. +ve rotation about an axis appears clockwise when
the observer is facing the direction of the +ve axis. Conversely, if
the observer is facing the -ve axis direction (as is the case for the
z axis in the second diagram), the rotation appears counter-clockwise.

Steve

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Received on Monday, 16 May 2011 15:17:19 UTC

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