An experiment
A Garmin Legend with WAAS capabilities was supported by a tripod and placed over a known control point with coordinates accurate to less than 1 centimeter. The device was connected to a palm pilot with Pathaway software and after the device was allowed to stabilize for at least three minutes was observed to have 8 satellites being received with all eight receiving WAAS corrections. The Palm device was activated and 100 coordinate pairs were observed over a 10 minute interval. The area was in the clear with no obstructions. The area should be considered ideal for gps observations

The 100 positions were averaged and 98% of the positions were within 15 feet of the average. The 2% were treated as anomalies such as a car passing and were stripped out of the data. The data was averaged again and 73% were within 12 feet of the average and 58% were within 10 feet. This average was compared with the true position and was under 5 feet in error. The vertical average was within 2 feet.

Conclusion:
The specifications for this gpsr state that with waas accuracy up to 3 meters (10 feet) can be achieved. The results from this single test appear to bear out this statement. Caution should be taken however, in that this was an ideal situation without tree canopy. Ten minutes is probably not enough observation time to truly test the hardware. Several observations of this type need to be made before any definite conclusions can be drawn.

If you are interested in duplicating this I will give you the software I used.
For data collection, Pathaway. It is available in Palm O/S and Windows CE. For averaging and graphics I used GPS UTILITY . There is a stripped demo version and a $45 licensed version. The monuments used for comparison were City of Fayetteville control monuments. Most counties such as Fulton, Dekalb, Gwinette, Cobb, Clayton, etc have gis control monuments you can find on-line. Please share your results if you perform a similar test.

Geo - Geek.

Geo - Geek

heh! heh!, yep, I confess, sometimes I am more interested in the tool than what it does.

If you just want to do a basic test and get a smiley for the effort, you can find my GPS Accuracy Checker virtual cache.

It is/was a base station for 1st-order surveys with centimeter accuracy.

Kenneth

I looked 3 times for that accuracy checker with the hint indicating I was within a feww feet, and still couldn't find it

That said, the area is still good for the accuracy check.

quote:

Originally posted by KVOM:
I looked 3 times for that accuracy checker with the hint indicating I was within a feww feet, and still couldn't find it

That said, the area is still good for the accuracy check.

Well if you really want to check it and get the smiley, I could meet you for lunch there one day and arrive early to make sure the grass is not too high around it.

Kenneth

quote:

Originally posted by nasty george:
<snip>...placed over a known control point with coordinates accurate to less than 1 centimeter. ...<snip>

Hey nasty george,

Since my GPS Accuracy Check geocache is I.T.P. (inside the perimiter), I'd like to place another one O.T.P.
Is the control point you speak of publically available where a virtual cache could be placed the same or similar to my current cache?

Kenneth

Sure! No problem. We have set about 30 monuments in Fayetteville and another 30 in Fairburn. The report is in .pdf,and has a photo, coordinates in lat/long and state plane coordinates of each monument. It also has elevations.I have it on a jump drive that we can download to your laptop at the august meeting, or I can burn you a disk if you will send a SASE to g white 5439 wahsega way lake city 30260.

Now, I checked out the cache you mentioned and was amused at the logs. So you got this guy with an etrek yellow that finds the monument, puts the device on the monument and waits until it zeros out and declares his gps is accurate to under a foot! Wow!. Actually if he observes a lttle longer he will notice that it will give results as much as 50 feet off depending on pdop, movement of the observer etc. If he were to plot these points, he would see this very erratic pattern develop which would in time approach a 50 foot circle with density near the center. A device with WAAS will give a much tighter circle. I highly recommend downloading a demo version of "gps utilities" and observing this on a laptop. It is encouraging that some gc'ers are beginning to look at their equipment as something other than just an appliance that provides an end result without understanding what is going on.

Also, there are some web sites that have already been written about in the discussion boards. Google ngs, usgs, for data sheets. They give locations for gps monuments at a general location. I will be happy to send you links, but if you are like me, you enjoy doing your own surfing.

ng

It is funny (to me at least), but the way I found out about geocaching, I was googling for web sites to find out how these GPS' worked. The technology really is both cool and amazing.

quote:

Originally posted by nasty george:
Sure! No problem. We have set about 30 monuments in Fayetteville and another 30 in Fairburn. The report is in .pdf,and has a photo, coordinates in lat/long and state plane coordinates of each monument. It also has elevations.I have it on a jump drive that we can download to your laptop at the august meeting, or I can burn you a disk if you will send a SASE to g white 5439 wahsega way lake city 30260.

Are those monuments base stations or general "benchmark" type disks like can be logged on gc.com?
I really appreciate the info, but one that is publically accessible (with little chance of razzing from nearby homes/dogs/drivers/etc) and preferably in NE GA outside 285 would be best.

I don't want this to turn into you doing all the work and me placing the cache, so if the ones you have are not base stations I can look into it further myself.

quote:

Now, I checked out the cache you mentioned and was amused at the logs. So you got this guy with an etrek yellow that finds the monument, puts the device on the monument and waits until it zeros out and declares his gps is accurate to under a foot! Wow!. Actually if he observes a lttle longer he will notice that it will give results as much as 50 feet off depending on pdop, movement of the observer etc.

The logs are interesting to say the least.
It really is more of a fun exercise than a test of accuracy.
I figure those who really care about accuracy and such will research more...the rest will just log a smiley and move on.

quote:

I will be happy to send you links, but if you are like me, you enjoy doing your own surfing.

ng

I had some interest in benchmarking, but lack of updated support for them in gc.com helped me lose interest.

Kenneth

Are those monuments base stations or general "benchmark" type disks like can be logged on gc.com?

I don't know what the criterion is for the benchmark logins. I don't do those since I am a professional and have to find them as part of my job. It would give me an unfair advantage if finders started competing. You know the "Nah na na na boo boo" stuff. I know Solar has put geocaching on hold and is doing a lot of benchmark hunting. What about it Charlie?

These monuments have not been "blue booked". That is, entered in the national registry according to NGS specs which can be quite stringint. These monuments have been set and measured through and have been subjected to the usual statistical tests such as a chi square evaluation and later on a rigorous adjustment. The coordinates are sub-centimer accuracy in x,y&z. They should be considered control stations and benchmarks. Sorry about the statistical gobbledegook but I don't know of any other way I can describe it.
ng