Post-processing

[Guest mjbgis]

I know post-processing of GPS data is a way of improving the accuracy of a coordinate after the fact by using data recieved from another known location taken at the same time. I thought this might be a good way of getting a better coordinate when placing a cache.

 

Does anyone know of a way of doing this?

 

Is this functionality limited to more expensive GPS units or can it be done with the inexpensive one's most geocachers are using?

 

I am using a magellan 315 but would be interested in hearing if other people are doing this with other devices.

 

Thanks,

 

Michael

[Guest topografix]

Post-processing of GPS data requires phase information which isn't available from your handheld Garmin, Magellan, or Lowrance GPS. The Delorme GPS unit has this capability, and they offer a post-processing program for it.

 

Do a web search on RINEX for more info.

 

- Dan Foster

TopoGrafix

Free GPS software at www.easygps.com

[Guest Iron Chef]

functionality limited to more expensive GPS units or can it be done with the inexpensive one's most geocachers are using?

 

I am using a magellan 315 but would be interested in hearing if other people are doing this with other devices.

 

Thanks,

 

Michael

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I just take several readings on two different days and times if the cache is local. Then I just average the numbers (if they are very close together). This seems to give a pretty accurate coordinate for those without software like myself.

 

------------------

-Iron Chef

_ _____________________ _

agefive.com/geocache/

"But a big booming voice from the sky is exactly what you have found..."

-Contact

[Guest JasonW]

Personally I put my Mag 315 in the cache spot while I'm busy making the cache up from my cache kit. By the time I've packed it all in and written my bit in the front of the log book, it's been there 15-20 mins and I reckon it's as good a position fix as it's gonna get.

[Guest Silver]

Most of the Garmin GPS units have a feature called "Position Averaging". This takes a series of readings and averages the differences from the many readings. Small timing differences and changing satellites can give you slightly different positions. This feature can minimize the errors. (I don't know if the Magellan units also have this feature.)

 

Another way to get more accurate locations is to use Differential GPS. This is a real-time correction feature that is broadcast in many parts of the U.S. Here in the Pacific Northwest the Coast Guard sends out many DGPS signals that you can use with your GPS unit, if you have a seperate compatable receiver.

 

WAAS is supposed to collect DGPS-like updates and send them down on regular satellite links. Only 2 satellites are currently operational over the U.S.

 

Hope this information helps.

 

Silver

[Guest MadGPS]

quote:

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Originally posted by Silver:

(I don't know if the Magellan units also have this feature.)

Silver

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Yup, the MAG315 has that averaging feature !!

 

MadGPS

[Guest MadGPS]

quote:

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Originally posted by Silver:

(I don't know if the Magellan units also have this feature.)

Silver

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Yup, the MAG315 has that averaging feature !!

 

MadGPS

[Guest fire23]

Does the ETrex Legend have the capability to position average? And, if so, how do I use this feature?

[Guest bob_renner]

No it does not. The position averaging was particularly usefull when SA was on. It is less of a necessity now, although some people still prefer the feature.

 

With my Legend, if I'm standing still, the lat/long readout will barely change. The least significant digit will change at the most by 2. However, I have noticed that if I'm moving and then stop, it takes several seconds (10-20) before the display settles down. It's almost as if the display is either delayed, or it assumes I'm still moving before it decides I really have stopped. However, once it does settle down, there is very little further change.

 

Bob

[Guest Mike_Teague]

position averaging has _nothing_ to do with _post-processing_...

 

do some usenet or even web searches on the topic...

[Guest Silver]

Agreed Mike.

 

However, since the request was for more accurate coords for a hidden cache, position averaging and DGPS were offered as alternatives.

 

Silver

[Guest Nemesis]

quote:

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Originally posted by bob_renner:

No it [the ETrex Legend] does not [do position averaging]....With my Legend....I have noticed that if I'm moving and then stop, it takes several seconds (10-20) before the display settles down.

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Yes, the eTrex does not have a position averaging option (maybe we should ask Gramin to add it ASAP in their next firmware upgrade for all eTrex models), it would be useful.

 

But, I have long suspected that the eTrex does do a form of short term position averaging. I appears that it averages the last 10 or 20 seconds of readings to calculate your current position (maybe giving older reading a lower weighting). I suspect that it porbably does the same with your change in position with time (your velocity). This would explain why it thinks you are still moving when you stop, the older velocities are still being used to estimate your future position.

 

Cheers,

Donovan Govan.