Subject:
|
Re: Science Interest
|
Newsgroups:
|
lugnet.robotics.handyboard
|
Date:
|
Sat, 7 Nov 1998 20:13:32 GMT
|
Original-From:
|
Max Davies <[mdavies@]stopspammers[CAM.ORG]>
|
Viewed:
|
2050 times
|
| |
|
|
> > My idea is to combine GPS and computer technology by building an
> > inexpensive hydrant finder. A GPS receiver could determine the pumpers
> > exact location, then search a database for the closest waypoint
> > (hydrant) near the pumper. A needle could swing to determine relative
> > bearing and distance.
This idea sounds very interesting, but I see 2 problems...
First, a GPS reciever doesn't actually contain a compass, so it cannot correctly
point you to another location while you are standing still. To determine what
direction its facing, a GPS receiver must be MOVING. It then compares its position
measurement from second to second, and using that information it knows where its
heading so it can report back to you which way to turn to get to your destination.
This should't be too much of a problem though, because with a good receiver once
you start briskly walking in any direction the receiver will very soon sync up with
your movement. When I say a "good" receiver I don't necessarily mean an expensive
one... I chose a Garmin GPS 12 which is quite inexpensive because it offers no
frills yet it has all of the basics needed for accurate position and track
measurements.
The second problem might be a killer for you... GPS receivers work by using
signals from orbitting sattelites operated by the U.S. Departement of Defence.
Although most publicly available GPS receivers are theoretically accurate to within
15 meters or better, the DOD deliberately introduces small error factors into the
sattelite transmissions to reduce the accuracy to about 100 meters. This is called
SA (Selective Availability) and the DOD does it to ensure that no hostile force
uses the GPS system for weapons system targeting. This makes a lot of sense, but
unfortunately it means that the GPS you use to try to locate your fire hydrant will
randomly have an error factor of up to 100 meters, which I fear could make your
system worthless.
Their is a possible solution to this 2nd problem, and it's called "Differential
GPS". To understand exactly why this is necessary and how it works, I suggest you
read up on GPS fundamentals. At www.howstuffworks.com (which I urge everyone to
visit, it's great) there is a very basic article on how GPS works, and it contains
links to sites with more details. In particular,
http://www.trimble.com/gps/howworks/aa_hw1.htm gives a superb in depth explanation
of how GPS works.
|
|
Message is in Reply To:
 | | Re: Science Interest
|
| Dear Capt. Rutledge, Your ideas sound very interesting! May I suggest that you join the following mailing list. It's a hotbed for this sort of discussion: (URL)Dear Professor Berg, (...) ***...*** Robbie Berg Department of Physics, Wellesley College (...) (26 years ago, 6-Nov-98, to lugnet.robotics.handyboard)
|
3 Messages in This Thread:
 
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
