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

axes and normalization of orientation events

From: Dean Jackson <dino@apple.com>
Date: Tue, 10 May 2011 09:22:56 +1000
Message-id: <FD7F7647-C465-4DE9-959A-A549D4FB4FB1@apple.com>
To: public-geolocation@w3.org
Hi,

http://dev.w3.org/geo/api/spec-source-orientation.html

We've got some comments on our iOS implementation that we're not normalizing to the values defined in the specification. That's our bug (although I'm not looking forward to the math to fix it).

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. Typically, the X axis is pointing forward (eg. for a plane it is the direction of travel). The Y axis passes from side to side. I'm not sure if this is worth fixing, but it did create some confusion for me as I was comparing Tait-Bryon angles to Pitch/Roll/Yaw and Euler.

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.

Dean
Received on Monday, 9 May 2011 23:23:32 GMT

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