RE: Position Heading Questions?

Hi Andrei,

So providing access to a compass for the purposes of correctly orienting a map isn't a valid use case?

Most of the use cases for device orientation also rely upon location.  The example I like is that of pointing my device at a building or billboard.  It also works nicely when you are navigating.

To say that it isn't valid to include it because it isn't acquired in the same way is disingenuous.  You seem to be assuming that speed is just the first derivative of position, which is strictly true, but doesn't always reflect the measurement method.  Speed can be obtained in different ways - teensy gyroscopes and the like are quite good for inertial positioning, but they only measure acceleration directly, so location is not natural to these devices (they need a bootstrap position to do that and errors accumulate etc...).  But they are great at measuring speed.  Would you also advocate taking speed out?

You really need to substantiate claims like "doesn't fit the current abstraction" and "completely foreign".  I don't buy the watchPosition() argument - if the position changes (any element) you get a notification.  If there was an orientation element, that would have to be included.

Cheers,
Martin

> -----Original Message-----
> From: public-geolocation-request@w3.org [mailto:public-geolocation-
> request@w3.org] On Behalf Of Andrei Popescu
> Sent: Monday, 17 November 2008 7:33 AM
> To: Greg Bolsinga
> Cc: public-geolocation
> Subject: Re: Position Heading Questions?
> 
> 
> Hi Greg,
> 
> On Sat, Nov 15, 2008 at 9:46 PM, Greg Bolsinga <bolsinga@apple.com>
> wrote:
> >
> > Hello --
> >
> > The Position object has a heading field. It is described as: "The
> heading
> > attribute denotes the direction of the hosting device". Is this the
> heading
> > of the vector of travel while moving, or the direction the user is
> currently
> > facing, no matter the direction of travel? The context of the
> following
> > field, speed, seems to indicate that this is the heading of the
> direction of
> > travel.
> >
> 
> You are right, the definition is ambiguous and it needs clarifying.
> Right now, heading denotes the direction of travel so it is a property
> of the movement of the device.
> 
> > However, I can see the use for a 'which way is the device oriented'
> > compass-style heading, as well as the direction you're traveling in.
> One can
> > be facing backwards to the direction of travel! :)
> >
> > What do you think?
> 
> I completely agree that orientation would be useful but I have the
> following problem with exposing it in this API: orientation is
> completely orthogonal to position. So far, the spec is only concerned
> with the where on Earth a device is. How that device is oriented
> doesn't fit the current abstraction and, if we were to add it, it
> would break the API in subtle ways. For instance, it would no longer
> be clear when the watchPosition() callbacks would be invoked, so we'd
> probably need new methods (watchOrientation() ?), etc. This is the
> reason why most other APIs I've seen cleanly separate the two
> concepts:
> 
> http://developer.apple.com/iphone/library/documentation/UIKit/Reference

> /UIDevice_Class/Reference/UIDevice.html#//apple_ref/occ/instp/UIDevice/
> orientation
> http://developer.apple.com/iphone/library/documentation/CoreLocation/Re

> ference/CLLocation_Class/CLLocation/CLLocation.html
> 
> 
> > I think having both fields is fun, but I'm not sure what
> > heading has to do with a location specification if I was going to be
> really
> > picky about it. :)
> 
> Well, you can think of it as an optimization. It is a property of
> movement (i.e. change in position), so in that sense, it is relevant
> :)
> 
> >No matter what, I think the Position object's heading
> > description needs to be clarified. I'd also like both types of
> headings to
> > be available, both with the "If the implementation cannot provide
> speed
> > information, the value of this attribute must be null." wording.
> >
> 
> As said above, I'd vote for keeping the device orientation separate as
> it really is a concept that's completely foreign to geolocation.
> 
> Andrei
> 

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Received on Monday, 17 November 2008 14:11:30 UTC