Subject: [Geopriv] Question on draft-linsner-geopriv-relativeloc-01

From: "Marc Linsner" <[email-masked]>
Date: Fri, 13 Jul 2007 13:30:21 -0400

Marc B., 

> 
> I am still a bit fuzzy on the orientation aspect, the reference point 
> to be exact. In your example, the reference is the elevator (assuming 
> there is only one elevator, and it is not part of a bank of shafts), 
> where does the 30 foot east 20 foot south come from?
> 

Taking your question literally, it appears you are asking about the location
determination mechanism.  From a very high-level viewpoint....Disclaimer:
I'm not an authority on this so proceed with caution (but I do have an
imagination)!

The location determination mechanism involves multiple rf measurements.
Imagine a floor of a building where 6 access points are deployed in a grid
providing overlapping coverage to the entire footprint (ignore/assume-no
overlapping vertical for a moment).  The deployment could yield a station to
'see' 3 of the 6 APs at any given time.  Of course, the same could be true
in reverse, 3 APs could see a particular station.  Gather RF measurements,
bidirectional, and you get 6 numbers to play with.  Intersect these numbers
with known measurements considering known local rf anomalies, and the result
is fairly accurate.  Take this result and offset it from the admin
determined reference point and you have useful data.

Assuming your question is human oriented....

There has been much discussion about using north-south-east-west.  Yep, it
doesn't take too complex of a building before the average Joe loses sense of
orientation upon entering (assuming Joe understood N-S-E-W at the outside
door).  Compare this to other associated locally significant data like, room
number, column id, cubicle number, etc.  All of these require some external
(to the dataset) orientation, a floor plan, or simply running around
figuring out the room numbering scheme.   The same is true with this
dataset, unless Joe tracks the number and direction of turns he made getting
to the 3rd floor elevator, he needs some help to find 30 feet east and 20
feet south upon exiting the elevator.  So, Joe may need to reference a floor
plan, maybe one that resides on the wall outside the elevator.  It just so
happens, these are readily available, and in a very abbreviated
non-scientific survey, many have a compass rose on them.  When reviewing all
the alternatives to N-S-E-W, the only one that appears more helpful, is to
provide Joe with go 6 feet turn right, go 8 feet turn left, go 3 feet turn
left.  The problem with the latter, is there is no guarantee Joe will be
facing the right direction at the start, besides the ability for a newly
installed cubicle wall to totally mess things up.

So, admittedly this format isn't utopia.  But it has been considered
valuable to many that have deployed it.

Again, it's additional locally significant data, not substitute data.
Current technology delivers this today.

I hope this helps.

-Marc L.-

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---

From: "Dawson, Martin" <[email-masked]>
Date: Sat, 14 Jul 2007 21:50:06 -0500

Hi Marc(s),

I don't have too much trouble with the orientation aspect. Compass
points work - assuming we don't worry about pathological use cases at
the North or South Pole. What we have is a presumed Cartesian
orientation and a 3D vector.

I understand that this proposal does not intend to quantify the location
of the reference point. That is, there is no encoding of the physical
location of the lift. I think the concept is probably best characterized
as "landmark relative" since the reference point is not a quantified
location.

I think (I don't know) that James W's point is that an explicit
relative-location object which can be applied to a reference PIDF-LO
provides the offset information while the reference PIDF-LO provides the
reference point. That way an arbitrary set of relative locations can be
applied to a single reference location which is explicitly quantified.
This mechanism would cover the use-case under discussion and be more
generic to boot. I also think that James feels that the presumption of
compass points for orientation is too restrictive.

Personally, I don't mind if this gets added. I do wonder whether
"landmark relative" is going to be most useful if constrained to this
specific form. "Down the corridor, second left turn, and 3rd door on the
right, from the top of the fire stair" is also a relative location to
the "fire stair" and one which might be a more commonly useful. But,
then, I can only offer free text if it's going to be an ancillary field
and not a fully-fledged relative-location codec/object.

Cheers,
Martin

-----Original Message-----
From: Marc Linsner [mailto:[email-masked]] 
Sent: Saturday, 14 July 2007 3:30 AM
To: 'Geopriv'
Subject: [Geopriv] Question on draft-linsner-geopriv-relativeloc-01

Marc B., 

> where does the 30 foot east 20 foot south come from?

Taking your question literally, it appears you are asking about the
location
determination mechanism.  From a very high-level
viewpoint....Disclaimer:
I'm not an authority on this so proceed with caution (but I do have an
imagination)!

The location determination mechanism involves multiple rf measurements.
Imagine a floor of a building where 6 access points are deployed in a
grid
providing overlapping coverage to the entire footprint (ignore/assume-no
overlapping vertical for a moment).  The deployment could yield a
station to
'see' 3 of the 6 APs at any given time.  Of course, the same could be
true
in reverse, 3 APs could see a particular station.  Gather RF
measurements,
bidirectional, and you get 6 numbers to play with.  Intersect these
numbers
with known measurements considering known local rf anomalies, and the
result
is fairly accurate.  Take this result and offset it from the admin
determined reference point and you have useful data.

There has been much discussion about using north-south-east-west.  Yep,
it
doesn't take too complex of a building before the average Joe loses
sense of
orientation upon entering (assuming Joe understood N-S-E-W at the
outside
door).  Compare this to other associated locally significant data like,
room
number, column id, cubicle number, etc.  All of these require some
external
(to the dataset) orientation, a floor plan, or simply running around
figuring out the room numbering scheme.   The same is true with this
dataset, unless Joe tracks the number and direction of turns he made
getting
to the 3rd floor elevator, he needs some help to find 30 feet east and
20
feet south upon exiting the elevator.  So, Joe may need to reference a
floor
plan, maybe one that resides on the wall outside the elevator.  It just
so
happens, these are readily available, and in a very abbreviated
non-scientific survey, many have a compass rose on them.  When reviewing
all
the alternatives to N-S-E-W, the only one that appears more helpful, is
to
provide Joe with go 6 feet turn right, go 8 feet turn left, go 3 feet
turn
left.  The problem with the latter, is there is no guarantee Joe will be
facing the right direction at the start, besides the ability for a newly
installed cubicle wall to totally mess things up.

I hope this helps.

-Marc L.-

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