Garmin 60CSx accuracy

[+GoBlue!]

Hi all,

 

so far, i'm really happy with the 60CSx....granted, I have nothing to compare it to, as I'm new to this & this is my first GPSr. I have found, though, that while it gets me in the general vicinity, it doesn't always get me as close to the cache as I thought it would (i.e., more than a 20' radius) even in light/no tree cover. I've seen others that were reporting 60-70'....I haven't had anything that bad....it just makes me wonder if I'm doing as well as the unit should provide.

 

Yesterday I marked my coordinates (each averaged > 50 times) & compared to the posted coordinates for a couple of caches. Here they area:

 

Posted: N 30 15.912 W 85 58.728

Mine: N 30 15.914 W 85 58.729

 

Posted: N 30 13.388 W 85 52.509

Mine: N 30 13.388 W 85 52.504

 

Of course when I look at these now, I see how close they are but when I was out there, it sure seemed to put me a fair distance away. Hehe. Unit accuracy usually is/- 20'. Perhaps this is to be expected!

 

Jim

[strumble]

 

Posted: N 30 15.912 W 85 58.728

Mine: N 30 15.914 W 85 58.729

 

Posted: N 30 13.388 W 85 52.509

Mine: N 30 13.388 W 85 52.504

Jim

 

Sitting in Wales and using MetroGuide NA v7 on my PC with MapSource, I thought that 13feet and 26feet was pretty good! I usually find there are in-accuracies between Garmin units and TomTom in the UK and as a result the speed camera locations can be up to 80feet out!

 

So I think [for what it's worth] that the locations will vary according to the 'unit' posting the location and yours!

The in-accuracies between my old eMap, iQue 3600 and the 60CSX was considerable!

[+TheRoundings]

That's 13ft and 26ft differences. Normal I think, it's the kind of accuracy I get. Remember that it takes two different GPSr' to compare and atmospheric conditions can have an influence as well.

[+gpsjeep]

Hi GoBlue,

Check it out this way. Instead of comparing the accuracy of your gps to that of a hidden cache, download the way point to a nearby benchmark and compare the accuracy to that.

http://www.geocaching.com/mark/

benchmarks are accurate while caches are close to accurate.

 

Hope this helps.

 

-Jeff

[ArtMan]

http://www.geocaching.com/mark/

benchmarks are accurate while caches are close to accurate.

Just to clarify, some benchmarks are intended for highly accurate elevation, and the horizontal position (i.e., longitude and latitude) is estimated. To verify the accuracy of your GPSr against a benchmark, look for the phrase "location is ADJUSTED" near the top of the benchmark page.

 

-ArtMan-

[+Sputnik 57]

Yep. Comparing your coordinates to those of the cache placer results in combining your error with theirs. You don't really know how accurate they were and can only guess from reading logs where other caches give the coordinates kudos or boos.

 

But heck, if it were easy, it wouldn't be fun!

[+PFF]

Hi, Jim:

 

As others have suggested, you can compare your readings with a benchmark having "adjusted" (not "scaled") coordinates.

 

I have tried the experiment using a GPS unit of the same general model as yours. My readings matched the published coordinates exactly, after a five-minute average.

 

In addition, my unit has taken me directly to benchmarks for which I've been searching. So, generally speaking, I believe you will be very, very pleased with your receiver's accuracy!

 

-Paul-

[+GoBlue!]

Thanks, all! Great advice. I'll see what benchmarks I can find in the area.

 

Best,

Jim

[+DiscGolfDiver]

I love the 60cs. The x should just be better.

[+blindleader]

Thanks, all! Great advice. I'll see what benchmarks I can find in the area.

 

Before you get too excited about measuring the "accuracy" of your GPS receiver, consider what is really happening.

 

The receiver doesn't really measure anything.

It syncs up its clock with that of the satellite it's receiving and then calculates the distance to that satellite.

When it has enough satellites, it calculates the receiver position.

 

Two identical receivers at the same place, with likely give the position as somewhat different.

the main variables that lead to this difference are:

-The two receivers might be using one or more satellites different from each other for their calculations.

-The almanac data for one or more of the satellites might be slightly older for one receiver than for the other.

-Two receivers using identical satellites with the same almanac data, might not be using data from the precise same moment. The satellite, going several miles per second moves more than a hundred feet in .01 second, giving a different set of position and range for the calculation.

 

The bottom line is that you can't really talk about the "accuracy" of the receiver, because it isn't a measuring device. How well it receives satellites (better and faster sync up), and what the software does in the way of fudging the results before showing them to you (Yes both Garmin and Magellan units do this) affect the accuracy of each particular fix. Every fix is different for the above reasons, so going to an accurately fixed benchmark will tell you how accurate the fixes you get at that place and time are, nothing more.

Edited November 8, 2006 by blindleader

[+Lasagna]

Add into your calculations that even after averaging your position, your unit is probably still telling you that it's got accuracy only to say 20ft or so. Add that same consideration into the original person who hid a cache for another 20ft. Conceptually (although not truly mathematically accurate -- there's a whole discussion thread buried somewhere on these boards about that) you could now be around 40ft off from the cache depending on if your measurement and that of the original were 180 degrees out of sync with each other.

 

Get close, then put down the GPSr and let it lock in on it's location while you use your powers of observation to determine where the cache is likely hidden.

[+apersson850]

The addition of two EPE values, e1 and e2, to obtain the total EPE, et, is done quadratically.

 

et = sqrt(e1 ^ + e2 ^ 2)

 

So if you have two values of 9.0 meters each, you get a combined inaccuracy of 12.7 meters.

 

It has also been shown mathematically that today, without any Selective Availability in effect, averaging doesn't give much in better accuracy, since there is unfortunately no way of knowing if the extra values you factor into the average actually are better or worse than those you already have.

[+tomtomgogo]

I have walked round a bush with a cache in it, the bush being about 4ft across and the tomtom shows me circling the cache

 

Not always so good in tree cover and you have to walk away from a road about 20ft before the snap on effect stops.