Wow, thanks Jack, the ROS specific part of your gps code will probably work
for us.  I think your right though, ROS should have a standardized gps msg
that can be linked through a standard gps-to-odom node that can do these
calculations for you given just your gps topic.  I really appreciate your
help, this should really save us a lot of time implementing and
troubleshooting these calculations.

Thanks,

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
William Woodall
Undergraduate Software Engineering
Auburn University
w@auburn.edu
wjwwood@gmail.com
256-345-9938
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


On Tue, Apr 27, 2010 at 11:10 PM, Jack O'Quin <jack.oquin@gmail.com> wrote:

> On Tue, Apr 27, 2010 at 7:39 PM, William Woodall <wjwwood@gmail.com>
> wrote:
> > We are trying to feed gps data into the ekf's /vo topic, and I have seen
> the
> > tutorial for swapping visual odometry out for gps, but I haven't been
> able
> > to find the units for x, y, z pose in the that Odometry msg.  I have
> poked
> > around in the source a bit, and I haven't been able to find any clues to
> the
> > units, though I imagine it is displacement in meters or something
> similar.
> >  Our gps outputs lat, long, altitude which we need to translate,
> obviously,
> > but I was just wondering if anyone could tell me the specific units the
> ekf
> > is expecting.
>
> We have an open-source ROS driver for the Applanix Position and
> Orientation System for Land Vehicles (POS-LV) in the
> utexas-art-ros-pkg repository. The device is a highly accurate GPS
> (and IMU) that was used by many vehicles that competing in the DARPA
> Grand Challenges.
>
> Although the device interface is probably not useful to you, the ROS
> part of the interface may be helpful. It translates the (spherical)
> latitude and longitude coordinates into (Euclidean) Universal
> Transverse Mercator (UTM) and publishes: nav_msgs/Odometry; /odom
> transforms; and its own applanix/GpsInfo topic.
>
>  http://www.ros.org/wiki/applanix.
>
> The (x, y, z) Odometry points are in meters. Formerly, we used UTM
> displacements from the start of the run, but more recently we found it
> helpful to simply round the UTM easting and northing values to offsets
> from a 10km UTM grid. That keeps the values consistent between tests
> in the same area, while limiting them to a convenient size. It also
> makes it easy to determine coordinates from a map.
>
> It would be good for the ROS community to agree on a common GPS
> message. Since none existed, we defined our own based on the Player
> GPS info message.
>
>  http://www.ros.org/doc/api/applanix/html/msg/GpsInfo.html
> --
>  joq
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