Re: [SeattleRobotics] Dead reckoning versus GPS for SRS Robo-Magellen contest

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• Basically you build a map of the area using the waypoints and other data you may collect. Then plot a path from the start to the end that avoids the obstacles.
Message 1 of 5 , Jul 4, 2005
Basically you build a map of the area using the waypoints and other
data you may collect. Then plot a path from the start to the end that
avoids the obstacles. That path might look something like:

(The robot is placed at the starting position pointed in a specific direction.)
1. Travel 100 feet straight ahead.
2. Turn 90 degrees to the left.
3. Travel 175 feet in that direction.
4. Turn right 75 degrees.
5. Travel 50 feet.
(Robot should now be within sight of the cone.)
6. Turn on the camera and begin scanning for the orange code.

distance travelled and make measured turns, which enables a robot to
execute instructions like the above.

For bonus points, put sensors on the robot to detect obstructions,
move around any such obstructions, all the while keeping track of
position and heading, making on-the-fly corrections to the pre-planned
course to arrive at the original desination and heading.

Actually, the real question is how do you use GPS to do this? Even
with a good fix, you only know your position within a circle that's 20
to 50 feet in diameter which is a big area compared to the entire
can't figure it out from your position data: given the error in your
position, you'd need to travel hundreds of feet to get a good heading,
which you can't do on the course. GPS receivers use doppler shifts in
the radio signal to infer speed and heading, which works great for a
car or airplane, but robot speeds (in this contest) are too slow and
bumpy to get good values from that technique.

I think GPS is a red herring for Robo-Magellan, at least as the

Carbon

On 7/4/05, Donna Smith <dsmith164@...> wrote:
> Hello all,
>
> I believe I understand the basics of dead reckoning,
> but I'd like to understand how other roboticists are
> using this in place of GPS?
>
> The main question using dead reckoning is how to
> utilize the given waypoint info using this technique,
> or what is substituted for this to get from A to B?
>
> Thanks for the feedback,
> Donna
>
>
>
> Visit the SRS Website at http://www.seattlerobotics.org
>
>
>
>
>
>
>
• The question on GPS is whether a differential ground station is within about 15 kilometers. If it is, the GPS accuracy can be as high as a 50% probability of
Message 2 of 5 , Jul 8, 2005
The question on GPS is whether a differential ground station is
within about 15 kilometers. If it is, the GPS accuracy can be as
high as a 50% probability of being within a 20 cm sphere.

automatically correct for the errors introduced by the satellite
position and timing signals from four satellites in orbit. It then
calculates four equations for four unknowns: time and its position.
Just like the twinkling of the light from a star, the GPS signals
from the four satellites are slightly perturbed when traveling
through the atmosphere, which is enough to vary the calculated
position. The differential ground station is in a known position,
and works the equations backward, to calculate the error in each
satellite's signal. It then broadcasts this info, and differential
GPS receivers apply this correction to their own calculations. The
speed of the vehicle really doesn't affect the results.

The question is whether the SeaTac airport has GPS landing
capability, and is broadcasting the differential correction signals.
Or if the Port of Seattle is doing the same for cargo ships.
• Speed doesn t effect the results but it does adjust the effects of the error in the reading. If the vehical is moving 30 mph having a +-10m reading isn t all
Message 3 of 5 , Jul 8, 2005
Speed doesn't effect the results but it does adjust the effects of
the error in the reading. If the vehical is moving 30 mph having a
+-10m reading isn't all that large; while traveling 1mph that same
error is devastating.

--- In SeattleRobotics@yahoogroups.com, "andymich2"
<andrew.michalicek@h...> wrote:
> The question on GPS is whether a differential ground station is
> within about 15 kilometers. If it is, the GPS accuracy can be as
> high as a 50% probability of being within a 20 cm sphere.
>
> automatically correct for the errors introduced by the satellite
> position and timing signals from four satellites in orbit. It
then
> calculates four equations for four unknowns: time and its
position.
> Just like the twinkling of the light from a star, the GPS signals
> from the four satellites are slightly perturbed when traveling
> through the atmosphere, which is enough to vary the calculated
> position. The differential ground station is in a known position,
> and works the equations backward, to calculate the error in each
> satellite's signal. It then broadcasts this info, and
differential
> GPS receivers apply this correction to their own calculations.
The
> speed of the vehicle really doesn't affect the results.
>
> The question is whether the SeaTac airport has GPS landing
> capability, and is broadcasting the differential correction
signals.
> Or if the Port of Seattle is doing the same for cargo ships.
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