Successful First Tour with an Etrex 30

[bryn]

Just completed a 1000km tour in France with the Etrex 30/City Navigator maps and am well pleased with the result.  Some random findings in no particular order follow:

1.  I initially adopted Francis's setup allowing cycling -err, not bicycling you understand - through menu, map, and computer pages just using the Back button.
 
2.  I didn't have time to setup his clever method of naming waypoints to indicate direction of turns, but just relied on keeping an eye on the magenta track on the map page.  I had created the complete track for each day on ridewithgps.com and then downloaded the tracks to the Etrex.  Show on map/Hide on map allowed only one to be displayed, and then depressing the joystick button when GO was displayed on the Track Map initiated the Track following function.  The Etrex creates its own waypoing/routepoints which are at randomly selected road high or low points - nothing as useful as major changes of direction, and no routing instructions.  So the distance to next waypoint info isn't very useful.  ISTR reading that someone here managed to get more useful routing directions using this function, but I didn't succeed.

3.  If you go off track to a shop/cafe/viewpoint it recomputes the distance to destination assuming you have to go all the way back to the start first, but corrects itself once you are back on the magenta line.

4. A couple of Duracell AA batteries lasted about 4 days.  The Etrex tends to keep working as long as possible, but then won't restart once switched off until new batteries are installed.  No doubt super hi-tech batts would have lasted much longer.

5.  On one occasion a complicated sequence of button pushing led the Etrex to freeze.  (It's a little knack I have with computers). Once turned off it would not turn on again.  Removing and reinserting the batteries fixed it. Very strange. (The next stage was going to be hurling it against a rock face). 

6.  I like to know what hills are coming up so I added the Elevation Plot page to the other 3 back button cyclable pages (thanks again Francis).  My companions were greatly cheered each time I told them there was another 2 hour climb around the next bend.

7.  You don't have to use the Menu/Adjustzoomranges sequence to change the zoom on the Elevation Plot page.  A forward or backward joystick movement will put the Etrex directly into the zoom change mode.  Then Back to get  back to the Elevation Plot and left/right joystick to pan back and forth along the elevation plot. Back again to exit the pan mode.

8.  Finally mastered the art of making a joystick Enter click (without unwanted up/down/left/right click) while riding:  tip of thumb on face of the Etrex, then rotate thumb downwards squeeeezing the joystick until it clicks.

9.  Really not sure whether the Barometer elevation function is necessary.  With GPS accuracy of 3m throughout, the GPS derived elevation was surely better then 10m and certainly better than I could get using my wrist altimeter (changing baro pressure and difficulty of getting spot heights to calibrate).

10.  As noted before my Etrex 30 significantly underestimates altitude gain (ride from an elevation of 400m to an elevation of 1000m and you should see an altitude gain displayed of at least 600m i'n'it, whatever the granularity).  An Edge 800 user was getting much higher readings.  My VDO 1.0+ bike computer altimeter gave an answer midway between the Etrex and the Edge.

11.  The screen can be difficult to read at times, even adopting full warp power on the display light.  Mostly I left the light at the lowest setting, ramping up to full brightness if some tricky turns were coming up. It becomes impossible to read during hailstorms and/or when covered in water.  A protective case is available, with what seems to be a semi opaque/100% reflective screen cover - I left it at home.

12.  This is the first tour where I did not miss difficult to spot turns, ride into farmyards or leave villages on the wrong (unmarked) road - the magenta line worked brilliantly.

13.  There was some really nice scenery on the way I'm told, but I was much too busy looking at my Garmin screen

Thanks to all here for the very useful advice given to me over the past months.

--
Bryn

[frankly frankie]

Interesting read, thanks bryn.

5.  On one occasion a complicated sequence of button pushing led the Etrex to freeze.  (It's a little knack I have with computers).

There must be a name for people like you! 

9.  Really not sure whether the Barometer elevation function is necessary.  With GPS accuracy of 3m throughout, the GPS derived elevation was surely better then 10m and certainly better than I could get using my wrist altimeter (changing baro pressure and difficulty of getting spot heights to calibrate).

Not sure what you're saying here.  I'm fairly convinced that barometric GPS types are 'better' insofar as they give a much smoother elevation plot which is a better representation of what actually happened, than the spikey GPS-derived plot would be.  In terms of accuracy, well of course you have a classic Catch-22 assuming the barometer is being auto-calibrated from the GPS anyway.  Even so, considering all the options (no barometer, auto-calibrated barometer, manually-calibrated barometer) I'm fairly sure that in the long term the auto-calibrated barometer (ie set up as straight out of the box) gives the best results.

We had a strange one in the Tarn Gorges a couple of weeks ago - both using Vista HCx (barometric) types, we noticed that both GPSs were reading consistently 35m higher than the roadside heights printed on the km-stones (bournes).  Throughout the rest of the trip they had been consistently within 10m, more like 5m usually.  There was a storm coming so I put it down to a weather front and rapid pressure drop.  Or (less likely, given 2 GPSs) a mis-calibration during a moment of restricted sky view, in the gorges.
We stopped overnight halfway along the gorge, and next day (fine weather restored) continued along that D907 - noting that the height offset was still there, despite an overnight switch-off and (I assume) subsequent auto-calibrate.  After a while we turned right onto the D43 to climb steeply out of the gorge - and within a minute we passed a bourne with a height matching our readings within 2m.
I can only conclude that the heights marked on the bournes all along the D907 in the Tarn Gorge are all wrong - either mistakenly (duff survey?) or deliberately, very strange.

13.  There was some really nice scenery on the way I'm told, but I was much too busy looking at my Garmin screen

I think this is a very real problem.  For me, riding with a GPS induces a kind of tunnel vision.  The only other thing that I've come across like it, is canal cruising, which has a kind of 'alternative reality' feel to it.

[Toady]

9.  Really not sure whether the Barometer elevation function is necessary.  With GPS accuracy of 3m throughout, the GPS derived elevation was surely better then 10m and certainly better than I could get using my wrist altimeter (changing baro pressure and difficulty of getting spot heights to calibrate).

Not sure what you're saying here.  I'm fairly convinced that barometric GPS types are 'better' insofar as they give a much smoother elevation plot which is a better representation of what actually happened, than the spikey GPS-derived plot would be.  In terms of accuracy, well of course you have a classic Catch-22 assuming the barometer is being auto-calibrated from the GPS anyway.  Even so, considering all the options (no barometer, auto-calibrated barometer, manually-calibrated barometer) I'm fairly sure that in the long term the auto-calibrated barometer (ie set up as straight out of the box) gives the best results.

The vertical accuracy of the GPS is significantly less* than the horizontal accuracy, and I guess the 3m you are quoting is horizontal accuracy.

I've tried to think hard about this - whether to manually or auto calibrate and so on, but it just confuses me.  I think that as ff says the out of the box solution is (probably) the best answer.  It's certainly the easiest one.

If you do a web search on gps elevation accuracy you will find some interesting articles, and even more confusing ones!

* ie less accurate ... so bigger value for the error.

ETA:  Crazy things can happen. I remember I changed the batteries (at a point not far from sea level) on one ride.  At this point the track plunged way below sea level and then gradually climbed back up - possibly as the GPS (60CSX) was recalibrating itself.  Still, it got me a few more total metres climbed, so I didn't complain.

[Wothill]

My Etrex Legend doesn't have the barometer to smooth out the altitudes but we also noticed strange comparisons with the roadside altitude posts both in the Pyrenees and the Alps. There was quite often a systematic and consistent variation between the GPS altitude reading and the markers all the way up a climb. Quite often there would be a disagreement even at the top where the GPS should have had a pretty good view of the sky. The most amusing readings were when going up (or down, except I pay less attention above 50kph) a steep sided valley or gorge when it would quite often carry on showing a progressively higher altitude even when the road was going down or vice versa. Harder to explain were some the readings as we went down the Atlantic coast: despite a very good view of the sky, the GPS would show us at a consistent 12m below sea level for ages. You might expect a barometer-only altimeter to show such an error if it hadn't been calibrated but I can't explain how the satellites could be so consistently inaccurate.

Alf

[frankly frankie]

I have sometimes experienced a spatial offset, between the the Track being recorded and the road as it appears on the map, which can last up to 30 minutes or so even with excellent sky view.  Of course the map could be wrong and the Track right (this could be checked later with Google Maps Aerial View) but generally I think not.  I'm guessing the GPS clock gets wrongly synched somehow (at the nanosecond level) and only corrects at lengthy intervals.  Any such spatial offset could also indicate a (bigger) elevation offset, of course.

[Kim]

Bear in mind that spot heights marked on road signs are probably using a different datum to the GPS receiver...

[Panoramix]

Bear in mind that spot heights marked on road signs are probably using a different datum to the GPS receiver...

It would be "Nouvelle Triangulation Française", nevertheless French altitudes on land have for origin the mean sea level in Marseille which musn't be too far off from WGS84.

To be honest I think that this is a surveying mistake.