RE: Uses cases and requirements for Orientation API

Hi Angel,

I think photo geo-tagging would be a good use case for this API.

Most geotagging solutions only support lat, long and altitude so far however
the EXIF specification[1] (aka, how the metadata is embedded within the JPEG
files) supports more fields than this.

     4.6.6 GPS Attribute Information
     GPSTrackRef - Reference for direction of movement  
     GPSTrack - Direction of movement
     GPSImgDirectionRef - Reference for direction of image
     GPSImgDirection - Direction of image

Of particular implementation note, the two 'Ref' properties require values
of either 'T' or 'M' to represent true and magnetic references respectively.
Whilst the compass proposal appears to include support for this, the
orientation spec doesn't have any mention.

The GPSTrack and GPSImgDirection properties are then just rational numbers
between 0.00 and 359.99, albeit potentially confusing as Martin picked up
on. The orientation spec includes the equation 360-theta in section 5,
however this can produce erroneous results when theta is 0. That is, 360 - 0
= 360 which then falls outside of the bounds defined by the EXIF spec, as
well as many other systems that deal with orientation. The onus would then
be placed on the consumer of the API to wrap 360 back around to 0 -
something that either needs to be included in the example given, or
something that should be handled by the publisher of the API (preferred).

[1] http://www.exif.org/Exif2-2.PDF


--
Tatham Oddie
au mob: +61 414 275 989, us cell: +1 213 280 9140, skype: tathamoddie


-----Original Message-----
From: public-geolocation-request@w3.org
[mailto:public-geolocation-request@w3.org] On Behalf Of Angel Machín
Sent: Thursday, 15 April 2010 9:25 PM
To: public-geolocation; Matt Womer; Lars Erik Bolstad
Subject: Uses cases and requirements for Orientation API

Hi all,

We are about to start the definition of a new charter for version 2.
Device Orientation will be one the central pieces of the new version and we
should continue the spec writing process. We count on the first Editor's
Draft that Andrei sent at the beginning of March
(http://dev.w3.org/geo/api/spec-source-orientation.html) and a proposal for
a Compass API contributed by DAP
(http://dev.w3.org/2009/dap/system-info/compass.html) so far.

There have already been some discussions around the coordinates and
reference system to use in the spec, units, etc... On the other hand our
first draft is still lacking uses cases and requirements (section
6) and we think that in order to better shape the spec and to have a
criteria to solve the issues that could be raised in the future, we should
start collecting those use cases and requirements.

That's why we ask members and interested people following Geolocation to
contribute uses cases and requirements for section 6 of the spec by replying
to this email.... and I am sure Matt would love not to have more "pizza
delivery" examples ;-)

Please note that the DAP's Compass API proposal contains three use cases in
section 1.2 which could be a starting point:
- Walking Turn-by-turn Route Navigation
- Show the user's Position and Orientation on a Map
- Annotating Content with Orientation and Location information

Thanks and best regards,

Angel