GeezerHiker

July 8, 2014

GPS – the adventure continues

Filed under: GPS, Hiking, Inaccuracy, North Cascades — geezerwriter @ 12:39 pm

Since my last post I have been locked in a death grip with Garmin’s “Help” desk about my new GPSmap 62stc handheld GPS unit. I write in, they respond with a condescending, patronizing reply that picks out one phrase to criticize and ignores the general thrust of my message. I then reply in detail (as I am sure you can believe) and it is picked up by a different “helper” who chooses a different irrelevancy to pick on, and offers a completely different “explanation” or “solution”.

This process started on June 16 and has gone through six or eight iterations. I was going to wait for a some sort of resolution before reporting back to this blog but it is becoming clear that they are so adept at ducking this issue that resolution is very unlikely. But in the meantime, I have accumulated enough evidence to be quite confident that I understand what is going on.

Are you ready?

I my previous post I included this sentence:

 The best I can come up with would be an unlikely and deeply conspiratorial attempt to rig the results to agree with the odometer. But they probably wouldn’t do that.

Since that “4.2 mile” hike toward Excelsior Pass on June 5, we have gone to the Church Mountain Meadows on 6/12, the Goat Mountain Overlook on 6/19, a Middle Fork hike on 6/26 and back to Church Mountain yesterday, July 3. I have tried out all of the suggested settings proffered by Garmin and several of my own and gotten the same sort of results as the Excelsior hike every time. And at least twice, we have been joined by Carl sporting his Garmin 62st device, which seems to differ from mine only in that mine has a camera. He has gotten very similar results and has made a major contribution to my sanity (or what remains of it.)

The responses from Garmin have ranged from the merely patronizing to the positively ridiculous. In response to the fact that the device was generating spurious points when we stopped along the trail one respondent made this suggestion:

… try to stop as little as possible.

Another was quite insistent that accuracy could only be achieved by setting the device to record a track point every second – 3600 points every hour. Never mind that a track can only hold 10,000 points, limiting the device to a trip of about 2 hours and 45 minutes. Never mind that a track of that length causes their own BaseCamp software to bog down to the point of being unusable. And never mind that the “every second” track I made coming down on Goat Mountain is every bit as inaccurate as the one I made going up.

Most of my time with them has been spent dithering over these inaccuracies, where there is no outside authority to settle any dispute. There are hiking maps and websites, which are notorious for their casual inaccuracies –  it was my word against theirs. So I attempted to focus all the attention onto one verifiable, repeatable, incontrovertible inconsistency:

Why does their own device and their own computer software report different lengths for the same track under different circumstances?

It took a couple of exchanges to wrench their attention away from the accuracy question but last week I finally got someone to admit that there was something questionable going on when the removal of one redundant point from a log of over 500 points caused its length to changed from 4.2 miles to 3.6 miles and that he would have to look into it.

Then … silence.

The intervals between responses had been one or two days, mostly, but a full week elapsed before I saw a new email at about midnight before Thursday’s hike. I chose not to look at it before the hike since most of their responses had been simultaneously irrelevant and infuriating (or, in homage to Stephen Colbert, infurelevant) and I didn’t want to be in a bad mood in the morning.

On the hike to Church Mountain Meadows there were even more interesting results than before. I set the device to record a reasonable numbers of “bread crumb” points and kept a frequent watch on it along the way. I could see that it was doing a good job of following the shape of trail, catching even minor changes of direction and only rounding the switchbacks a tiny bit; I was confident that I had a very good track. I also was carrying my old Garmin 60CSx.

We stopped for lunch at a spot where all my previous experiences on Church told me the distance should be about 3 miles. I took the following readings from the devices:

  • 62stc Odometer: 3.55 mi
  • 62stc track: 3.4 mi
  • 60CSx Odometer: 2.9 mi
  • 60CSx track: 3.05 mi

I turned off the track logging on the new 62stc at this point, but didn’t save the track, yet. While I was sitting in the snow for the next half hour or so, I checked the 60stc now and then, watching the odometer go from 3.55 to 3.64 to 3.74 and by the time we got up to start hiking back, to 3.82. (That’s why I had turned the track logging off – so all that spurious junk wouldn’t be added to the track log.) All this time the device was sitting stock still on the top of my pack at 4950′ in an open meadow, showing excellent accuracy of about 2 meters (7 feet). Gaining an imaginary quarter mile in half an hour seems like pretty bad behavior, but long experience has driven my expectations for GPS odometers to be very, very low. But that’s another story.

As we prepared to start down the trail, I turned the tracking back on, saved the track (which still showed the 3.4 miles) and a minute later decided to use the “tracback” feature to show the distance back to the trailhead along that new track. Understand that I still thought it was an accurate track, just that its reported length was off  by almost half a mile.

And Lo! and Behold! The device now showed the distance to the trailhead as 3.0 miles!

When I got home and uploaded the stuff to BaseCamp, I got the usual nonsense: the track length showed as 3.4 miles until I deleted one point, whereupon it also changed to 3.1 miles. I ran the track through my spreadsheet and it gave 3.06.

The Bottom Line

So the old 60CSx track was right on the money at 3.05, and the 3.0 on the “tracback” and the 3.1 in BaseCamp can be chalked up to roundoff error.

All the other numbers reported by the 60stc are sheer bullfeathers.

Back to the Garmin “Help” Desk

So then I was ready to read the response from Garmin that I had avoided. There was some more patronizing stuff, but the gist was contained in this paragraph:

I hope this helps to explain this isolated incident that you were experiencing. This is an extremely rare problem. Unfortunately, the only way to really explain this error is to contribute it to corrupt GPX data on your device.

So, ignoring the fact that this was a brand new device when this stuff started happening and that another person’s device was getting the same results, Kris had come up with an “reason” that conveniently would invalidate all the previous data that Carl and I had accumulated, and attribute it to my not knowing how to disconnect the device from my computer!

[ short pause while the lingering rage gradually subsides…]

At the risk of my declining sanity…

Kris had given instructions on how to purge the dread corruption from the device, but since it works quite well around town, I would have to wait to test the inanity of his/her directions. But I couldn’t wait so on Sunday morning I performed the purge and headed over to Stewart Mountain (a big foothill, actually) to check on the progress of the logging operation that is likely to obliterate some of the trails over there. The conditions there are not nearly so challenging for the GPS as our real mountain hikes, but it might be enough to generate some good (i.e., bad) data.

I stopped at a little knoll in an old clearcut when the new device’s odometer just happened to read exactly 2.00 miles; the track log said 2.0; the old GPS’s track was 1.9. I was expecting the “tracback” function to shave a little off that 2.0 mile track length and was disappointed when it didn’t. I headed home.

Back at the computer, however, the old bug reappeared: deleting one redundant point changed the length to 1.9 miles and my spreadsheet came up with 1.895.

I sent this information off to Garmin and finally got the first response that was neither patronizing nor inane:

This problem has been reported. We are still researching this to find out what is causing this and how to correct this. I have added your information/file to the case. We will contact you when we have more information.

Hmm. We shall see.

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