Side By Side Unit Test

[+geojibby]

So I went caching with my friend today. We both recently upgraded from our eTrex H units. I got the GPSMAP 60Cx and he got the Oregon 300. Both awesome units. I assumed though that the GPSMAP 60Cx would have greater accuracy than the Oregon unit. However, today, my unit was saying I had (6-7m) 21 feet accuracy while his Oregon had 8 feet! I typically get 3-4 meters accuracy but today my unit was way off. His Oregon was bang on. How can this be??? We were in bald prairie, no canopy over head, cloudy weather. Is my GPSMAP 60Cx more accurate in its accuracy reporting???? Very strange. Any ideas?

[Baumer]

because the Oregon is a much newer, more sophisticated unit?

[stevensj2]

So I went caching with my friend today. We both recently upgraded from our eTrex H units. I got the GPSMAP 60Cx and he got the Oregon 300. Both awesome units. I assumed though that the GPSMAP 60Cx would have greater accuracy than the Oregon unit. However, today, my unit was saying I had (6-7m) 21 feet accuracy while his Oregon had 8 feet! I typically get 3-4 meters accuracy but today my unit was way off. His Oregon was bang on. How can this be??? We were in bald prairie, no canopy over head, cloudy weather. Is my GPSMAP 60Cx more accurate in its accuracy reporting???? Very strange. Any ideas?

Different situations - such as canopy cover like you've mentioned - as well as the satellite constellation and positioning at certain times - will affect different units differently.

 

Try it out several more times, and see if this result is consistent, or if on other days your unit reports more accuracy.

 

Also remember that the accuracy of satellites and their positioning reporting functions are purposely degraded for consumer use. While many units will report accuracy of +/- 8ft (I've even seen 8" before!) these numbers are just estimates, and the true accuracy and precision of the unit is much different.

 

Because of this, most newer consumer units will perform about the same, as far as accuracy goes since they are all receiving slightly "bogus" info from the sats. The only thing that will affect differences in performance/accuracy among them are chipsets/antenna style, WAAS ability, and differential correction. How the unit handles those factors will contribute to their overall performance more than anything.

 

No (consumer) unit could be made that would have an error of 0m or even within 4 ft. The unit might estimate that kind of precision or better, but it can only do as good as the signal its getting, and the satellites aren't sending signals with that type of accuracy.

Edited April 18, 2009 by stevensj2

[+Klatch]

So I went caching with my friend today. We both recently upgraded from our eTrex H units. I got the GPSMAP 60Cx and he got the Oregon 300. Both awesome units. I assumed though that the GPSMAP 60Cx would have greater accuracy than the Oregon unit. However, today, my unit was saying I had (6-7m) 21 feet accuracy while his Oregon had 8 feet! I typically get 3-4 meters accuracy but today my unit was way off. His Oregon was bang on. How can this be??? We were in bald prairie, no canopy over head, cloudy weather. Is my GPSMAP 60Cx more accurate in its accuracy reporting???? Very strange. Any ideas?

It wasn't "accuracy", it was EPE or estimated position error. The algorithm which calculates EPE can make the results look different if they are not the same in the two units.

[NordicMan]

Well, the Garmin 60's are indeed awesome GPSr's but, as time goes by newer models come along with better technology.. sooner or later it's going to have to pass it's "legendary" throne onto another.

 

Having said that, make sure both GPSr's have brand new / fully charged batteries when testing!

[+geojibby]

Well, the Garmin 60's are indeed awesome GPSr's but, as time goes by newer models come along with better technology.. sooner or later it's going to have to pass it's "legendary" throne onto another.

 

Having said that, make sure both GPSr's have brand new / fully charged batteries when testing!

 

That might have been the problem, but both of our units were actually running low on power. This is a very interesting situation to me. I think my little eTrex H also advertised 2m of "accuracy" but my GPSMAP 60Cx has only ever gotten 3m. Can those patch antennas be better than the quad helix double-bubble goodness?!!??!

[4x4van]

Klatch hit the nail on the head. It isn't "accuracy" that you are seeing listed on the GPS screen. It is that particular unit's opinion of it's estimated accuracy at that time. Two different models likely have different calculations written into their software that they use to come up with that "guess". Even two identical models will rarely if ever give the same EPE readings. About the only thing the EPE is good for is judging the relative accuracy of a unit from minute to minute as compared to itself, not compared to other units.

[+g-o-cashers]

That's right, EPE or "GPS Accuracy" as it is called on the newer units is not a reliable means for comparing accuracy between units. As an example, GPS Accuracy on the Oregon has changed over software releases, early on it was typical to see it in the 20-40' range, now it isn't uncommon to see 8'-10' after some recent software updates.

 

I have both units and in side by side tests if you compare their tracks on the same hike day over day the 60csx is still a more reliable unit, although the Oregon has seen some improvements in this latest beta phase. Because of the antenna design/chip set I'm skeptical if it will ever be quite as good as the 60csx.

Edited April 19, 2009 by g-o-cashers

[+geojibby]

That's right, EPE or "GPS Accuracy" as it is called on the newer units is not a reliable means for comparing accuracy between units. As an example, GPS Accuracy on the Oregon has changed over software releases, early on it was typical to see it in the 20-40' range, now it isn't uncommon to see 8'-10' after some recent software updates.

 

I have both units and in side by side tests if you compare their tracks on the same hike day over day the 60csx is still a more reliable unit, although the Oregon has seen some improvements in this latest beta phase. Because of the antenna design/chip set I'm skeptical if it will ever be quite as good as the 60csx.

 

But here's the thing. When we did the side by side comparison and tried to navigate to a waypoint like a geocache, the Oregon seemed to be more bang on in leading you right to ground zero. I had let the 60Cx average some waypoints, like 130 measurements, 450 measurments, etc. And when I went back a few days later, trying to navigate to that averaged waypoint, it was nowhere near the spot that I had averaged the coordinates for! (even when I averaged at 3.3m "accuracy" - when we went back it was 20 feet off). We have not done the track test, but in terms of waypoint "accuracy" the Oregon seemed to be smackin' my 60Cx around like Mike Tyson in an ear munching match! I don't think my unit is defective, in fact I stood side by side with another 60Cx unit yesterday at an event cache and they were reporting almost exactly the same. Aside from trying to find a surveyed bench mark, it's probably impossible to tell exactly if the unit is off or not...

[+Red90]

A geocache is not a reliable method for determining accuracy since the owner's coordinated may not be good.

[Ken in Regina]

What Red90 said.

 

There is only one way to determine the accuracy of your unit (not to be confused with the EPE that the unit reports, which is nothing more than a wild-a** guess). You must take it to a benchmark and let it sit right on the benchmark for a time. Then compare the location on the benchmark to the location that the GPS is telling you. That will give you a better idea of the capability of the unit than anything you've tried so far.

 

The different EPEs being reported by the two units and the cache finding results may be true, but you'll never know for sure until you compare the actual location that both display at a benchmark or two with known and highly accurate locations.

 

All you know for sure right now is that the two units probably use different methods for guessing their relative positional accuracy and that the Oregon's calculated position seems to better match the GPS units that were used to set the caches in the first place. Of course for caching use, if this last difference persists, if the Oregon continues to be consistently better for finding cache ground zeros in your area, the real accuracy may be irrelevant to you.

 

Which unit is better for you for caching is a different question than which one is "more accurate".

 

Continued testing with your friend is the best way to determine the answer to the first question.

 

Testing them both against some benchmarks is the only way to settle the second question. Benchmarks can be as interesting to find as caches, so it's a fun exercise no matter what the results.

 

...ken...

[+geojibby]

 

All you know for sure right now is that the two units probably use different methods for guessing their relative positional accuracy and that the Oregon's calculated position seems to better match the GPS units that were used to set the caches in the first place. Of course for caching use, if this last difference persists, if the Oregon continues to be consistently better for finding cache ground zeros in your area, the real accuracy may be irrelevant to you.

 

Thanks for this post - this quote matches my experience thus far. On the caches that I hid with my eTrex H, the other patch antenna units (like the Oregon) seem to find bang on. Also, a cacher in our area uses the same 60Cx unit I do and I can find his bang on. So perhaps the GPSr family series are accurate at finding caches placed by units of their own series - makes sense. Might also explain why these units are so off when compared to each other in practice.

 

Ken, how do you find Canadian benchmarks?

[Ken in Regina]

When it comes to the accuracy of the location information in existing caches, keep in mind that many, perhaps the majority, of caches on here were set with older technology receivers. It's also a good bet that many - regardless of the technology of the receiver - were set without letting the receiver settle long enough.

 

My brother-in-law doesn't even have a GPS receiver and he taught me what I believe is the most important lesson I will ever learn about geocaching. On my very first hunt, while I was trying to nail ground zero with my GPS deep in an old-growth forest of huge firs, he found the cache. When we got close he ignored the GPS and pulled out the description he had printed before we started out. I had walked within 5 feet of the site at least twice but because I was trying to nail the coordinates I would never have found the cache. He found it in under 5 minutes and it wasn't easy.

 

Here's a good place to start. The Waymarking forum is accessable from the main index page here on Geocaching.com. Waymarking can be as much fun as caching.

 

http://www.Waymarking.com/cat/details.aspx...49&exp=True

 

Have a read through this page. The first few links take you to databases in the Canadian Spatial Reference System. To access those databases you need to register in order to log in. It doesn't cost anything so it's no big thing. Once you're logged in you can find stuff close to you by clicking on a map, similar to one method of finding caches on here.

 

...ken...

[Ken in Regina]

Okay, here's one benchmark you might want to avoid when testing your GPS accuracy. It's off by a little.....

 

http://www.deseretnews.com/article/1,5143,705298412,00.html

 

...ken...

[+geojibby]

Okay, here's one benchmark you might want to avoid when testing your GPS accuracy. It's off by a little.....

 

http://www.deseretnews.com/article/1,5143,705298412,00.html

 

...ken...

 

Hehhehhe..... thanks!