Comments on DeviceOrientation Event Specification, Editor's Draft 24 August 2010

Hi,

My name is Claes Nilsson and I work at Sony Ericsson in Lund, Sweden. I am a member of the W3C DAP WG. Currently I am not a member of the Geolocation WG but I plan to join.

I have, together with sensor experts at Sony Ericsson, reviewed the DeviceOrientation Event Specification (http://dev.w3.org/geo/api/spec-source-orientation.html ). As I have not followed the WG's earlier discussions on this specification please forgive me if I am addressing issues that already has been discussed.

Our comments follow::

Section 4.2 Device Orientation Event:

-          We propose a  boolean 'needsCalibration' property that indicates that the magnetometer needs calibration.

-          In the current version of the specification the device orientation data is provided as Euler angles. However, there are other ways of providing sensor data. I looked at the following interesting presentation: http://www.youtube.com/user/GoogleTechTalks#p/u/0/C7JQ7Rpwn2k . At the end of the presentation different ways of exposing sensor data for developers are described. There are apparently limitations with Euler angles that occurs when the device is pointing right up, Gimbal lock, http://en.wikipedia.org/wiki/Gimbal_lock. Do you consider this limitation acceptable meaning that applications using the Device Orientation Event have to be constrained taking the Gimbal lock problem into consideration?

So, have you considered to also provide orientation data as a rotation matrix? We also want to make an API that is simple to use for developers and we think that it would be beneficial for application developers to be able to get access to device orientation data in the form of a rotation matrix in addition to Euler angles for each axis. One benefit for this is for example that WebGL uses rotation matrixes, which will remove the need for complex transformations if the information is to be used with WebGL.  Also note that the Android sensor manager supports rotation matrix.



Section 4.4 Device Motion Event:

-          As the attribute "acceleration" does not include the gravity component we propose to call it "linearAcceleration".



Section 5 Examples:

-          It would be nice to have more examples on the Device Motion Event.







To consider for later versions of the specification:



Raw Magnetometer Data Event:

-          We propose a new event that delivers raw magnetometer data (microtesla) in 3-axis. Use cases are for example metal detector and a compass using own algorithms. Note that a raw magnetometer data API is provided in the Android Java environment.



Best regards
Claes Nilsson M.Sc.E.E
Senior Technology Strategist
CTO - R&T Europe - UI/App/Web

Sony Ericsson Mobile Communications
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E-Mail: mailto:claes1.nilsson@sonyericsson.com
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