Etrex Accuracy Vs Etrex H

[+lambdacachealpha]

Hello!

 

I was wondering if anyone has tested the older Etrex units out head-to-head against the newer "H" models which supposedly have better accuracy?

 

I just want to know if the newer model is worth the $$ differance...

 

also, if anyone has any etrex model up for sale please let me know.

 

Thanks!!

 

LambdaCacheAlpha

Edited September 22, 2010 by lambdacachealpha

[+ecanderson]

In open skies and wide open terrain, the extra sensitivity isn't critical. As soon as you duck into the trees, the newer units with higher sensitivity chipsets start to make a real difference in the accuracy of the readings. You can score a simple eTrex H (or even upgrade to a Venture HC) for so little money these days that I wouldn't even consider a "non-H" model.

[+julianh]

The difference is in the SENSITIVITY rather than the ACCURACY.

 

When both units have a reasonable fix, they will yield pretty much identical position coordinates. However, all of the H-series models (high sensitivity) will get and hold a fix where older low-sensitivity units will not. Low-sensitivity units will typically have trouble getting or holding a fix in canyons, under moderate tree cover, in the "urban jungle", etc. High-sensitivity units can typically get and hold a fix deep in canyons, under very heavy tree cover, deep in the street canyons of New York, and often indoors as well (very handy if you forget the way to your bathroom!)

 

Don't even think about it - get a high-sensitivity unit!

[+teamhillside]

The difference is in the SENSITIVITY rather than the ACCURACY.

 

When both units have a reasonable fix, they will yield pretty much identical position coordinates. However, all of the H-series models (high sensitivity) will get and hold a fix where older low-sensitivity units will not. Low-sensitivity units will typically have trouble getting or holding a fix in canyons, under moderate tree cover, in the "urban jungle", etc. High-sensitivity units can typically get and hold a fix deep in canyons, under very heavy tree cover, deep in the street canyons of New York, and often indoors as well (very handy if you forget the way to your bathroom!)

 

Don't even think about it - get a high-sensitivity unit!

 

I have an old (non-H) eTrex, and my brother in law has the Legend H. Whereas my old etrex rarely gets accuracy greater than about 15 feet, his was reporting 2-3 feet (and right on top of the cache).

 

A no-brainer for me - get an H model!

 

Matt

[+gpsblake]

2-3 feet accuracy is impossible with the MM.xxx format. However, in a dense environment, the H series will outperform. Both units will get you to the cache area eventually, millions found geocaches in the woods before the days of SIRF-III chips and faster hardware. Also, if your getting an Etrex without the high sensitive antenna, you're buying a unit that is several years old.

[+ecanderson]

2-3 feet accuracy is impossible with the MM.xxx format.

Agreed on the need for the "H" unit, but still doubtful about the above in terms of the logic, if not the reality.

 

While the unit displays in one format or another as selected by the user, the internal data isn't being calculated at the displayed resolution. It's calculated at a finer resolution and converted to the lesser displayed resolution.

 

Assume a world of perfect calculation of GPS data to some arbitrarily crazy number of decimal points. The unit could put you right on the spot for any point of an equal or lesser unit of measure.

 

That said, we often see drift of 0.001 in latitude and longitude on the most stable of units, so we're talking at best 4' E/W and 6' N/S of potential drift.

[+Jeep4two]

I have an Oregon 400t (and recently a Dakota 20) that I've used along side my eTrex Legend (non-H, older unit).

 

As others have said you can't see any difference in performance under 'ideal' conditions. However under tree cover, cloud cover or in more challenging conditions (in a steep valley, under tree cover on a cloudy day for example) I've found the old eTrex Legend virtually useless while my Oregon 400t holds lock admirably.

[+gpsblake]

Agreed on the need for the "H" unit, but still doubtful about the above in terms of the logic, if not the reality.

 

Let me explain. Even if your actual unit were accurate to the millimeter, it still could not be 2-3 feet accurate on a cache because of the MM.xxx format... Example... N 80 00.000 can be N 80 00.0004 or N 79 59.9996... about a 5 foot difference... that's why you can't have 2-3 foot accuracy using the MM.xxx format... Now if the format were MM.xxxx then technically it would be possible. Then you throw in the variance of the unit that set the cache, and the error difference grows even greater.

[+Jeep4two]

I think it might also be worth noting that the 'accuracy' as advertised by your GPSr while in use is an estimation of the accuracy based on the signal quality at that point in time. Key word here is ESTIMATION.

 

If a GPSr shows accuracy below a meter it's likely a flaw in the algorythm used to calculate the EPE (Estimated Position Error) on the GPS. I've never seen any of my Garmin units read below 10 feet of accuracy.

[+ecanderson]

Agreed on the need for the "H" unit, but still doubtful about the above in terms of the logic, if not the reality.

 

Let me explain. Even if your actual unit were accurate to the millimeter, it still could not be 2-3 feet accurate on a cache because of the MM.xxx format... Example... N 80 00.000 can be N 80 00.0004 or N 79 59.9996... about a 5 foot difference... that's why you can't have 2-3 foot accuracy using the MM.xxx format... Now if the format were MM.xxxx then technically it would be possible. Then you throw in the variance of the unit that set the cache, and the error difference grows even greater.

You're assuming that the "accuracy" somehow depends upon the displayed coordinate system. It doesn't.

 

If someone placed a cache at 40.000000 105.000000 and I used a coordinate system that only displayed in whole degrees, if my unit were perfectly accurate, I could and should still be able to land at 40 by 105 exactly with my "feet of error" showing 0.

 

Or perhaps we're talking at crossed purposes here. Granted, if I am looking at the displayed coordinates, I can't get any closer than the granularity of the coordinate system. But if I'm looking at the distance to the target, I can get as close as the device is capable of resolving internally. So in my example above, I could be standing on 40.000000 by 105.000000, my unit show only the gross coordinates 40. and 105., but the distance to the target could be 0' or 1' or 2' or ...

 

So I guess what I'm saying is that the "distance to target" (for example, "feet" from GZ) is entirely independent of the resolution of the displayed coordinates since the former is not computed from the latter. If it were, you'd always see distances jumping in about 6 foot (only N/S of target 0.001) or 4 foot (E/W of target at my latitude 0.001) or about 7 feet (0.001 error in both N/S and E/W). That isn't what you see because that's not where the distance computation comes from.

 

What is relevant to the target distance are a ) the real accuracy and internal resolution of the GPS unit, and b ) the granularity of the units being used to display the distance to target.

Edited September 23, 2010 by ecanderson