Two more thoughts on accuracy

[Guest OregonSurveyor]

One (actually two) more comments on this question of accuracy:

1) When hiding a cache, try to obtain a reading when you first arrive at the chosen location, and then take another reading just as you are about to leave. The intent here is to take two readings which are spaced apart in time, ideally more than an hour, but even less time will help. If your GPS has an averaging feature be sure to use it also.

2) Another little trick is to take a set of reading while standing a set distance (say for example 30 feet) away from the cache in all four cardinal (N, E, S, W) directions, then compute a mathmatical average of these four points (or 5 points if you include the coordinates of the geocache itself). This will tend to reduce the error created by tree canopy or multi-pathing, etc.

Take the time to get good readings, searchers that follow you will appreciate it!

 

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Lat. N 45d-30.6875'

Long. W 122d-37.2055'

Elev.=172.97'

king6kids@hotmail.com

[Guest Kerry]

In theory Point 2 (similar to the Golf Ball averaging in another post) sounds practical but without hindsight it's really still an unknown quantity (similar to averaging) and time will/can/might/does change the whole result.

 

The following image shows the difference between a real world application (basically done concurrently) using high order GPS equipment compared to the type of equipment generally used for caching along the lines of averaging/interesting cardinals (similar to the "Golf Ball" method).

 

Hopefully the diagram/comments will be self explanatory?

 

 

The position solution of the handheld is still well under SPS accuracy specs but the "integrity" of the solution is the unknown. Also note the "consistent" relative accuracy for the handheld positions.

 

If one looks at Arffer's "Repeatable Accuracy" diagram's (in other posts) then maybe if I had come back a few hours latter and did the same exercise with the handheld the result would have probably been entirely different? It's an unknown and in practice the perceived position could have been that distance (or further) in the opposite direction? Nobody really would know unless there is something to compare it to?

 

Jut a bigger image of above http://www.cqnet.com.au/~user/aitken/gps/1085.jpg

 

The point is all the theories are fine but in practice one simply can't be sure of what's happenning at a particular time.

 

Cheers, Kerry.