Question about averaging my readings.

[geoSeeker5]

I've read that by averaging our readings over time, thereby using different sat signals, we can more accurately guess where we are. But I haven't read anything about the proper way to do this.

 

Please tell me if this is the right approach.

 

Collect some position data over time in the decimal format. Then calculate the average and convert back to degrees.

 

Is it really that simple?

[+Jamie Z]

quote:

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Originally posted by geoSeeker5:

Collect some position data over time in the decimal format. Then calculate the average and convert back to degrees.

 

Is it really that simple?

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Yes, if you'd like it to be. That technique is fine.

 

The most important thing is to take these readings over a long period of time. The GPS satellites orbit the earth twice a day, so if you wait an hour or two (or even longer... go back the next day, for example) the satellite geometry will be different and may give a different reading. Since you really can't know which of these several readings are closest to the actual, an average is a good estimate.

 

Averaging a number of readings taken during a short period of time probably won't increase your accuracy at all. If the geometry is poor, then all those closely-spaced readings might be incorrect.

 

Jamie

[+brdad]

I agree, do it over time if possible and approach from different directions. What I have done for my fist hide is kept averaging only if accuracy was less than 25'. Then when I went out to do another average, I made a waypoint on my GPS using my current average, just to see how close it would lead me to the exact location. After 5 or 6 trips to the site, my GPS has always been within 10 feet of the actual location.

 

Hopefully any finder's readings will be that close too, will find out soon if I get my description written and approved...

 

Some days you're the dog, and some days you're the hydrant.

[+The Leprechauns]

Brdad, I'm really sorry, but that is WAY too much information about where you hide your fist.

 

x-x-x-x-x-x-x-x-x-

A computer without Microsoft software is like a dog without a brick tied to its neck.

[+MountainMudbug]

quote:

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.... that is WAY too much information about where you hide your fist.

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ROFL!

 

"The clarity is devastating. But where is the ambiguity?

Over there, in a box."

[+brdad]

quote:

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Originally posted by The Leprechauns:

Brdad, I'm really sorry, but that is WAY too much information about where you hide your fist.

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Oh, I want to edit that, but I'm gonna leave it!

 

Caught me on that one Lep...

 

Some days you're the dog, and some days you're the hydrant.

[Kerry.]

Averaging by its very nature does just that gives one an average, doesn't necessarily mean we know more accurately where we are but.

 

So many variables there's about a 50% chance of having more confidence in the result and about 50% of having less confidence. What one doesn't know at the time is which 50% one is dealing in.

 

Averaging has more to do with confidence in the result more so than accuracy as averaging can actually decrease accuracy.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[Kerry.]

Averaging by its very nature does just that gives one an average, doesn't necessarily mean we know more accurately where we are but.

 

So many variables there's about a 50% chance of having more confidence in the result and about 50% of having less confidence. What one doesn't know at the time is which 50% one is dealing in.

 

Averaging has more to do with confidence in the result more so than accuracy as averaging can actually decrease accuracy.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+MrGigabyte]

Unfortunately, you may think you improving you accuracy by averaging over a short period of time, but in reality, you are not (except maybe trapping a gross error). Ten minutes of readings means 20 or so waypoints recorded with no consideration to the geometry of the satellites. To be of any value, the geometry must change. The birds move 30 degrees an hour, so waiting even half an hour is a big improvement.

 

All you may be doing is getting an average of bad data. It may be accurate but it is not precise. They may all be within 5m of each other, but they may also all be 50m out! Multiple readings over a short period of time will ALL have the same system errors included. That is, the same SV's are used and most likely, no new almanac data in introduced. Multi-path is the only error than can be reduced over a short time period.

 

How you get the average is irrelevant. Whether by rigorous (least squares) or semi-rigorous (guesstimate) methods does not make any difference, if the average you come up with is based on questionable readings.

 

Moving is very important if it means moving to a location where the view of the sky is improved over the exact spot you have hidden or looking for the cache. Simply moving to the other side of a tree or even 10m or more may improve your precision by several orders of magnitude. You can always manually adjust the latitude and longitude later knowing that 0.001 minutes is roughly 2m.

 

Get to know your satellite screen. It is the best information your GPSr provides.

 

Keep an eye on the satellite page. Wait until you have the best reception and geometry and then set a waypoint. If you have to move 5m to get out of the tree shadow, then do so. Moving that 5m may increase your accuracy by a factor of 10. Now keep watching the satellite page for as long as you can stay there. Take more waypoints. Just wait, be patient, improve your view of the sky and take multiple waypoints ONLY when the satellite view is good. The longer, the better.

 

Now, just zoom right in on your map screen on your GPSr and manually select the best position (be it a recorded waypoint or not) from the grouping of waypoints you recorded.