Subject: [Geopriv] Uncertainty Use Case

From: "Thomson, Martin" <[email-masked]>
Date: Fri, 24 Mar 2006 13:49:04 -0600

Uncertainty is a reality of location technologies.  The theory is explained in draft-thomson-geopriv-geo-shape, but I thought it might be helpful to show an example of how uncertainty can be useful.

Since location-dependent routing is the hot topic of the moment, so we will take a very simple example, with an ascii art circle I ripped off the web somewhere.

Take the following routing choice between zone A and B for the point marked by the "><".  If all I know is the point, then the choice is easy...

  __________________
                    |             Zone B
                 >< |
   Zone A           |
                    |
The same applies to a circle that fits wholly inside of zone A.  However, if you have a larger region of uncertainty, the choice can become trickier:

             _.-""""-._
           .'          `.
  ________/_________     \     B
         |          |     |
         |       >< |     |
         |          |     |
      A   \         |    /
           `._      | _.'
              `-....+'
                    |
In fact, as the area of the circle increases at some point it becomes less likely that the target is in zone A than zone B.

This can also be a use case for method.  In the absence of uncertainty, knowing the location determination method can actually be useful.   Near such a corner, a location based on a cell tower only may receive different treatment to a GPS determined location.  (A cell tower is a bit of a bad example - a cell tower location is a very bad thing to include as just a point; a person is almost never standing right at the cell tower - a better example might be GPS vs. some radio timing technology.)

Cheers,
Martin

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