I have to agree with Bean. I have an eTrex Legend C and·I don't think its basic GPS accuracy is much better (maybe when WAAS is available), and it cost over $250.
Actually there are a couple methods to provide better accuracy, both require puchasing a new receiver. DGPS and WAAS enabled receivers obtain·an additional source of information to provide better error correction. DGPS uses ground based "beacons" which have a fixed known location, the error it receives between its reported location and known location is transmitted and picked up by DGPS receivers. WAAS is the newer version and uses a geostationary sattelite, the ground based beacons compute thier errors, report it to the WAAS satellite which the WAAS enabled GPS reciever uses to calculate the local error from finding the data of the nearest ground beacon.
BTW you aren't getting 5 m resolution, a GPS can only estimate its error. 10m is pretty much the best that can be obtained from a standard GPS.
Here is a table of the accuracies availible from the different systems:
GPS 10m
DGPS 1-5m (depending on how close you are to a beacon)
WAAS 3m
LAAS 1.5m
LAAS is like WAAS, but you must be closer to the beacon in order to use it, also it only used near airports to provide airplanes with accurate landing information.
Addendum, the Parallax GPS is a WAAS receiver. This is the best you can hope to achieve in accuracy (DGPS can be more accurate, however the regions where this higher accuracy is obtainable are quite small).
WAAS availability will get you only +/- 3-meters @ 95% of the time.
US Military GPS equipment, while much more accurate, does require
the ocassional decryption key to get this accuracy.
If you need high accuracy of certain points then averaging of lat/lon
readings for a period of time will get you the accuracy. If you need
this accuracy while moving then I don't see how you'll do it with the
Parallax GPS module.
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-Rusty-
--
Rusty Haddock = KD4WLZ = rusty@fe2o3.lonestar.org
**Out yonder in the Van Alstyne (TX) Metropolitan Area**
Microsoft is to software what McDonalds is to gourmet cooking
It wouldn't work. This is a competition where the robot must navigate over given waypoints on a course. The course data·isn't availble until 5 minutes prior to start of the competition. At this point the location hasn't been released and rules forbid using, scanning or navigating the location once released.
I did find out some more things about GPS and some ways to increase accuracy which I thought people would want to know. By using these corrections factors in the code the accuracy is greatly improved.
First,·use microseconds for timing. The smaller the timing units used the better. So by calculation out the next GPS signal at one second based on microseconds you get a more accurate fix on your location.
Second, use division out to 1,000 decimal points or more for all math calculations. Again, the more specific the better.
Third, Adjust the altimeter to the barometeric pressure and location for that day. This data is available from aviation resources and is transmitted 24 hours a day via radio for aviation uses.·For example an airport might be at 392.7 feet above sea level with a pressure of 33.4 for the day.·This data will reflect on the GPS accuracy and can be easily attained. These adjustments will also be a signifcant increase in accuracy.
Finally, run a projection of your location based on the last known cordinates. Example, if the GPS shows you moving at 30 mph then calculate out, based on microseconds, how far you should travel at 30 mph based on·inches (or cm). Figure out from that what should be your new location·and then use that to help eliminate errors by cross checking your GPS data - new and old.
Are you provided the precise coordiates of the starting position? If so you can use it and the measured reading to provide some additional accuracy (that may drift after a while if the race takes a long time).
Well if you do obtain the "true" location of the starting point (Not GPS generated, but the actual coordinate), you can compare that with what your GPS provides to get an offset. This will act in the same way a beacon does, and with the other techniques you mentioned should get you going.
Alas, that offset is only good for a short period of time -- the time it takes for
the list of tracked GPS satellites to change. Once even a slightly different set
of satellites is in the calculations (even by one) the offset will be, usually, quite
different. I believe the time a given offset is valid is somewhere around 12-15 minutes.
If this offset were good for the rest of time, WAAS and DGPS would be essentially
useless.
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-Rusty-
--
Rusty Haddock = KD4WLZ = rusty@fe2o3.lonestar.org
**Out yonder in the Van Alstyne (TX) Metropolitan Area**
Microsoft is to software what McDonalds is to gourmet cooking
I agree that it is not a permanet solution, however every little bit helps. If for any reason motion is stopped for a few seconds then everything can recalibrate.
AIman
Posts: 531
Comments
You're asking an awful lot from an $80 GPS. I'm surprised it's that accurate.
Bean.
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Cheap used 4-digit LED display with driver IC·www.hc4led.com
Low power SD Data Logger www.sddatalogger.com
SX-Video Display Modules www.sxvm.com
Don't mistake experience for intelligence. And vis-vera.
Post Edited (Bean (Hitt Consulting)) : 10/13/2006 6:39:29 PM GMT
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- Rick
BTW you aren't getting 5 m resolution, a GPS can only estimate its error. 10m is pretty much the best that can be obtained from a standard GPS.
Here is a table of the accuracies availible from the different systems:
LAAS is like WAAS, but you must be closer to the beacon in order to use it, also it only used near airports to provide airplanes with accurate landing information.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Paul Baker
Propeller Applications Engineer
Parallax, Inc.
Post Edited (Paul Baker (Parallax)) : 10/13/2006 8:02:47 PM GMT
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
US Military GPS equipment, while much more accurate, does require
the ocassional decryption key to get this accuracy.
If you need high accuracy of certain points then averaging of lat/lon
readings for a period of time will get you the accuracy. If you need
this accuracy while moving then I don't see how you'll do it with the
Parallax GPS module.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
-Rusty-
--
Rusty Haddock = KD4WLZ = rusty@fe2o3.lonestar.org
**Out yonder in the Van Alstyne (TX) Metropolitan Area**
Microsoft is to software what McDonalds is to gourmet cooking
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There's nothing a good wack with a hammer won't fix
Darn I let the white smoke out again
I did find out some more things about GPS and some ways to increase accuracy which I thought people would want to know. By using these corrections factors in the code the accuracy is greatly improved.
First,·use microseconds for timing. The smaller the timing units used the better. So by calculation out the next GPS signal at one second based on microseconds you get a more accurate fix on your location.
Second, use division out to 1,000 decimal points or more for all math calculations. Again, the more specific the better.
Third, Adjust the altimeter to the barometeric pressure and location for that day. This data is available from aviation resources and is transmitted 24 hours a day via radio for aviation uses.·For example an airport might be at 392.7 feet above sea level with a pressure of 33.4 for the day.·This data will reflect on the GPS accuracy and can be easily attained. These adjustments will also be a signifcant increase in accuracy.
Finally, run a projection of your location based on the last known cordinates. Example, if the GPS shows you moving at 30 mph then calculate out, based on microseconds, how far you should travel at 30 mph based on·inches (or cm). Figure out from that what should be your new location·and then use that to help eliminate errors by cross checking your GPS data - new and old.
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John R.
8 + 8 = 10
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
the list of tracked GPS satellites to change. Once even a slightly different set
of satellites is in the calculations (even by one) the offset will be, usually, quite
different. I believe the time a given offset is valid is somewhere around 12-15 minutes.
If this offset were good for the rest of time, WAAS and DGPS would be essentially
useless.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
-Rusty-
--
Rusty Haddock = KD4WLZ = rusty@fe2o3.lonestar.org
**Out yonder in the Van Alstyne (TX) Metropolitan Area**
Microsoft is to software what McDonalds is to gourmet cooking
Not perfect but helpful.