Hi,
You can always break it down to: transforming some absolute coordiantes
of an augmented object from a coordinate system in some model of space
around you to camera coordiantes and/or screen coordinates of your device.
To be able to do that you have to know your 6DOFs [1] relative to that
absolute coordiante system. This can be achieved in various ways. For
example by using GPS to get a approximate position, then load a 3D model
of your surrounding area from a server and get your orientation by
matching pictures measured by your devices video camera aginst this
model. There are a lot of other approaches out there, just an example....
I don't think that sending your 6DOFs to a server and let the server
compute all object shapes into you local coordinates and deliver them
back to you is faster then getting some absoulute coordinates from the
server and compute the rest directly on the device.
But If you once know your 6DOFs in global coordiantes it is easy for
your device to get globally refernced objects, for example delivered via
GeoRSS or GeoJSON, displayed on the screen of your device augmenting the
real object through your screen.
Cheers
Christian
[1] http://en.wikipedia.org/wiki/Six_degrees_of_freedom
Chris Goad schrieb:
whats the problem here? Its simple coordiante transformation stuff...
or do I miss something?!
PS
There is a substantive issue here to do with local coordinate
systems. When representing the features of a particular object it is
sometimes useful to employ coordinates local to that object, and
represent separately the position of the object in the world or
relative to its parent in a heirarchy. Reasons: The coordinates of
features relative to the object may be known more accurately than
global position of the object, and an AR device's relative position to
the object might also be known with greater precision than its global
position. The object may not have a fixed position (eg AR on board a
ship). The representation is more compact.
3d modeling formalisms support this (and full GML does too), but
GeoRSS, GeoJSON, and KML do not. This is probably an argument for
going to represententations built for 3d in the first place for AR
applications where local coordinates play a necessary role, but
concievably there is a niche for our lightweight geo standards
extended by addition of a transformation node.
-- Chris
----- Original Message ----- From: "Christian Willmes"
<[email protected]>
To: "Mike Liebhold" <[email protected]>
Cc: "Ron Lake" <[email protected]>; "geojson"
<[email protected]>; <[email protected]>; "GeoRSS"
<[email protected]>
Sent: Friday, August 28, 2009 6:00 PM
Subject: Re: [Geowanking] [georss] [Geojson] simple 3D geocode for AR
Hi,
whats the problem here? Its simple coordiante transformation stuff...
or do I miss something?!
The device gets the geocoordinates from the web, and computes those
using its own position and orientation to local camera coordinates....
its that simple... I think. ;-)
regards,
Christian
Mike Liebhold schrieb:
Ron Lake wrote:
The most logical coordinate
system for locating such items is a rectilinear coordinate system
(x-y-z
frame) centered (origin) at the focal point of the camera.
What's the use case?
In most cases, we probably can assume that the geo-annotations exist
independent of the viewpoint; e.g. a viewer should be able to see
the note attached to a restaurant from any perspective as they pass
on a sidewalk, or drive by.
In that case, we need absolute coordinates, not relative to the
camera perspective.
imho
Mike
Cheers
Ron
-----Original Message-----
From: Mike Liebhold [mailto:[email protected]] Sent: August 28, 2009
2:05 PM
To: Ron Lake
Cc: Joshua Lieberman; [email protected]; geojson; GeoRSS
Subject: Re: [georss] [Geojson] simple 3D geocode for AR
Ron Lake wrote:
The use of geographic coordinates for [location of things in the
field
of view relative to the camera] likely does not. [ make sense]
Ron,
This is really counter intuitive, Can you explain what you mean?
- Mike
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Joshua Lieberman
Sent: August 28, 2009 11:03 AM
To: [email protected]
Cc: geojson; GeoRSS
Subject: Re: [georss] [Geojson] simple 3D geocode for AR
In both GeoRSS GML and GeoJSON, some explicit CRS needs to be
specified to use 3-coordinate locations. The simplest one for
GeoRSS seems to be epsg:4979 ( urn:ogc:def:crs:EPSG:4979 ). It
would need a slight modification to support the GeoJSON long-lat
encoding. Otherwise use GeoRSS Simple and the elev property.
e.g.
<georss:elev>346</georss:elev>
<georss:point>42.3234 -173.234134</georss:point>
Well-known text description of 4979
(http://spatialreference.org/ref/epsg/4979/ )
GEOGCS["WGS 84", DATUM["World Geodetic System 1984", SPHEROID["WGS
84",
6378137.0,298.257223563, AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]], PRIMEM["Greenwich",0.0,
AUTHORITY["EPSG","8901"]], UNIT["degree",0.017453292519943295],
AXIS["Geodetic latitude",NORTH], AXIS["Geodetic longitude",EAST],
AXIS["Ellipsoidal height",UP], AUTHORITY["EPSG","4979"]]
Josh
On Aug 28, 2009, at 1:05 PM, Ron Lake wrote:
Sorry my example should have been
<Point id = "P1" CRS = "http://www.blah.bla/standardCRS.xml";>
<coordinates>100 200 150</coordinates>
</Point>
But the argument is the same. Similar encodings can be made in JSON
etc.
R
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Andrew Turner
Sent: August 28, 2009 9:57 AM
To: [email protected]; GeoRSS; geojson
Subject: Re: [georss] [Geojson] simple 3D geocode for AR
Simplest?
Just include a 3rd coordinate in GeoRSS-Simple point or GeoJSON
point.
No, this is not explicitly valid. But you see where that discussion
gets us. Long windy roads of elusive semantic talk (arguably
necessary
in the lon term, but not simple or useable *now*, which is when
people
are building these tools).
If we lose interest without achieving a near term concensus,
developers will just do arbitrary, different solutions. Give them a
simple answer now, even if it makes your strict-validation-only-skin
crawl just a little bit. :)
So I say just do it, and we'll catch up with documenting it as uses
emerge.
Also, KML already supports 3D points.
Andrew
(via mobile)
On Aug 27, 2009, at 4:35 PM, Mike Liebhold <[email protected]> wrote:
A friend wrote me with a request for clarification on a topic we've
discussed many times here, but every time we've approached a
consensus the answer seems elusive.
Many devleopers are starting to create applications for iPhones and
Android phones to view location specific data through the
viewfinder using the -imprecise- capabilities of the built in gps
and compass and applications platforms like Layar.
The question:
What is the -simplest- way to geocode a geoannotation in 3D using
geoRSS/Atom, geojson, KML ....?
(Is there a practical reason why WGS '84 shouldn't be implicit, and
a CRS lookup NOT be required?)
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