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Accuracy: How much is hardware, how much software?


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With the interesting comparisons of different Garmin units -- Colorado vs 60CSx, Oregon vs Colorado, etc., I was wondering if anyone here knows GPS receiver chips well enough to say how much of the differences are due to different hardware, and how much is due to the software that does the calculations?

 

Different units use chips made by different manufacturers. Are certain ones known (quantitatively, not anecdotally) to be more accurate and more reliable than others? Are the chip sets in Garmins newer units unable to create as accurate a track as the older ones, regardless of what Garmin does with the data it gets from those chip sets? Should they (or any other maker) be able to get significantly better accuracy by improving the algorithms in their software? Or have they gotten it "as good as it gets"?

 

I realize the software can only interpolate/extrapolate so much from the data that comes off the sensor, so what I'm really thinkig is, can we expect a more accurate track from the existing chip sets in the future, or are we getting everything we can from this hardware?

 

BTW, what I mean by "accuracy" is, how precisely it puts data points to exactly where I am on a path. That is, if I'm walking at the top of a 300m cliff, and it shows my track at the bottom of the 300m cliff (or on the other side of a river, etc.), then that's not very good.

 

Thanks for any education.

Edited by Manatee87
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BTW, what I mean by "accuracy" is, how precisely it puts data points to exactly where I am on a path. That is, if I'm walking at the top of a 300m cliff, and it shows my track at the bottom of the 300m cliff (or on the other side of a river, etc.), then that's not very good.

 

 

With this point I think you are introducing another layer to the discussion: map accuracy. Any current GPSr particularly with WAAS when receiving a good signal should be able to get you on the correct side of river or cliff. If the map you are plotting the data on top of is of low quality or you are zoomed in way closer than the base map's reference scale, then it could be a whole different issue. For example, the topo map included with my CO 400t has a scale of 1:100,000 or roughly 1 inch = 1.5 miles if it were printed on paper. Now zoom in on that map with your GPSr so that you're looking at 1 inch = a couple hundred feet, it's still the same data with a pretty large margin for error.

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True, the accuracy of the map is also important, so for the sake of this discussion I'll say let's forget the map. I'm interested in how accurately the unit can possibly mark the real-world path that my feet took -- even if the map shows me walking down the middle of the river. :lol:

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I think you can also safely say that units with high-sensitivity receivers, regardless of manufacturer, always involve some kind of tradeoff in less than ideal reception conditions. For example, older, less sensitive receivers would simply lose lock in heavy tree cover. In effect, this resulted in "inifinte" EPE since you no longer had any idea where you were. Newer, more sensitive receivers maintain lock in this situation. But you pay a price for that ability. The receiver has to pay attention to reflected (multi-path) signals in order to maintain lock. This means higher EPE in challenging conditions -- but still lower than "infinite." It also means that your reported position may "wander" a bit when standing still.

 

So, you may not get maximum possible accuracy in your reported position in challenging conditions. Similarly, your outbound and return tracks may not match very well. But you do have a decent idea of where you are, and you do have a continuous track. You would not have had these things with a less sensitive receiver.

 

There are several layers of firmware involved in any GPSr. I suspect, without knowing much about how any of it is constructed, that there is always some room for improvement. Certainly, there is room to fix large problems like the widely reported "drift" error on the Colorado. On the other hand, these are recreational units which sell for hundreds, not thousands, of dollars. I'm not sure how much incremental improvement (as opposed to bug fixes) we can really expect in these units.

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On the other hand, these are recreational units which sell for hundreds, not thousands, of dollars. I'm not sure how much incremental improvement (as opposed to bug fixes) we can really expect in these units.

 

This is exactly what I was thinking... unless there is some significant change in the current technology, there is a natural ceiling for the accuracy of recreational units since they make real-time calculations on single-frequency pseudorange measurements. In short, it's the hardware that is the limitation.

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There are several layers of firmware involved in any GPSr. I suspect, without knowing much about how any of it is constructed, that there is always some room for improvement. Certainly, there is room to fix large problems like the widely reported "drift" error on the Colorado. On the other hand, these are recreational units which sell for hundreds, not thousands, of dollars. I'm not sure how much incremental improvement (as opposed to bug fixes) we can really expect in these units.

What I don't understand is why Garmin seems to have so much trouble with SOME current models, and not at all with others!

 

I understand that the higher sensitivity introduces the risk of introducing some inaccuracy in poor reception conditions (due to multi-path errors etc), but most recreational users accept this trade-off as being better than having NO position-fix at all, which is what you used to get with older units. (In critical applications, such as landing a plane, it may be safer to have NO position fix rather than an inaccurate one, forcing you to use alternative navigation instruments, but for recreational users, knowing where you are within 50 metres or so is generally better than not knowing where you are at all.)

 

I also understand that the high sensitivity units can generate spurious "movements", especially under sub-optimal reception conditions, and this in turn generates some software issues about when to record movement as being genuine, when to filter it out as being probably spurious, and the impact this can have on the trip computer, total climb, total descent, etc.

 

What I DON'T understand is why some models will from time to time record spurious track logs for significant periods, even when the reception is reported as being pretty good, while other models never exhibit this problem at all (and will record an accurate track-log when used side-by-side with one of the problematic models). Certainly, I have NEVER seen this problem with my Summit HC, for example. The spurious track log can apparently persist long after you have moved back out into the open, but turning the unit off and on will apparently resolve the issue immediately.

 

What is also strange is that this problem seems to have been introduced to the Vista HCx range with late release software updates - presumably as part of the attempt to sort out the trip computer / total climb issues. It is clearly a software issue (not hardware) in this case, and it is one that Garmin MUST resolve.

 

I have yet to hear from single recreational user who thinks that having an accurate current location is LESS important than having a reasonably accurate trip meter! (But I don't understand why you can't have both - like my Summit HC. Maybe Garmin should ditch all of the current software for the Vista HCx and the Colorado etc, and use the current Summit HC software code as a starting point for another go! :lol: )

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On the other hand, these are recreational units which sell for hundreds, not thousands, of dollars. I'm not sure how much incremental improvement (as opposed to bug fixes) we can really expect in these units.

Does anyone make "professional-grade" hand-held mapping units that (perhaps) _do_ cost thousands of dollars -- and are incrementally more accurate? Or does that sort of hardware only appear in big, bulky units? I've never looked at the GPSr market beyond Garmin/Magellan/Delorme hand-helds.

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Not bad. You can pick one up for $5K. I was about to click and add it to my cart when I saw... it only supports USB 1.1. That's a deal breaker for me. :lol:

 

I see you can also rent one for $950/month.

 

Probaby a good move. I'm sure if you just hit the trail or do a little caching, you are bound to run across somebody who has one and would be happy to give you a demo before you upgrade :)

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