My comments about the etrex Vista C
From: Nacho (ncc1701zzz_at_hotmail.com)
Date: 12/12/04
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Date: Sun, 12 Dec 2004 20:16:38 GMT
Hello.
I had the opportunity this week to try my new Vista C in a 500km travel
with walking excursions at sea level. I would like to share with you my
impressions and to comment some bugs I have found.
My firmware is 2.10 and it is an European Vista C.
I have MetroGuide 6 loaded with my regions of interest. Also I have
loaded World Map with overlapped regions. Why? Worldmap has the light
beacons in the coast indicated. As I went to the beach, I would like to
know the lighthouse beacons color, position, frequency, etc, just as a
curiosity.
The travel was from Madrid (Spain) to Oviedo (Spain). The Vista C worked
well in the country with some problems in the city, losing lock
sometimes, and regaining it in a short time. I could see about 10-12
satellites and really receiving about 75% of them in the country, if
there are no mountains. I suppose that the vehicle's structure and
myself block some signals.
I have had GPS before so the behaviour is more or less like a etrex
Legend I had.
About the new things, the barometric altimeter and the compass, I can
say that they work fine but with some limitations.
About the altimeter, well, it is barometric so the barometric pressure
changes affects it. It is autocalibrated with the GPS signals, and it is
a great idea. Barometric changes are slow, but GPS changes are fast, so
the GPS has time to calculate a average elevation with the GPS signals
and then, calibrate the altimeter. A fast change in the barometric
altimeter is sure to indicate a change in elevation.
It may take some time to calibrate. In land is harder to see, but at sea
level is easier. One doubt I have is what is "0 meters"... Above mean
sea height? Minimum height?
When I reached the coast, at about 5 meters over the medium sea level,
the barometric altimeter said "-2 meters". But with a good satellite
coverage, it slowly started to grow up to about 7m, and stayed there.
Not bad ;)
The next day, due to pressure variations, it said "23 meters" at sea
level. Again, after about 10 minutes, it reached 7-8 meters. Of course
if you know the right altitude, you can calibrate it manually and then
the automatic calibration will correct the pressure variations.
Also I have found that multipath affects also to the autocalibration
process. I had in some places multipath while near a mountain and the
altitude decreased about 10 meters, while I was in the same place with
the GPS in a table. Well, GPS altitude would have also changed ;)
So I think the barometric pressure altimeter works fine if you let it
some time for autocalibration.
About the compass, I found some problems at first until I understood the
whole working process...
The compass must be calibrated. The calibration process is done doing
two turns with the compass leveled. Ok, thats fine. But the level you
have while calibrating, must be preserved while measuring! If not, wrong
values will be shown.
An example: you put the GPS horizontally and calibrate it doing two
turns. Then you get the GPS and levels it a little to get a better view
of it. Inmediatly, the "Hold Level" appears and the measure is wrong.
BUT you can calibrate it with the GPS slightly inclined to you, and then
the measure will be correct if you maintain the inclination. If you then
put the GPS over a table, the "Hold Level" will appear. I suppose that
this problem is solved in a 3-axis compass like some Magellan have.
I'm very happy with the GPS and the color screen looks great!
The Metroguide map is in general very accurate where there is map ;) I
knew that Spain is not very detailed, but it did a good job in the
places I was. Well, an important road (rather new) was not in the
database but I suppose that it will be in the new version. And there was
lots of rural roads missing.
About the lighthouse beacons in the Worldmap, the frequency and color
was right in the two I could see but the position of one of them was
completely wrong. It was a the wrong side of the bay, so in a foggy day
you could end in the middle of the beach instead of the port ;)
Now the bug report. I don't know if somebody at Garmin is reading this
or if I should send it to someone...
First, I have found a important bug in combination with the Metroguide
maps loaded. In a point of my trip, I found a weird behaviour in the GPS.
It stopped redrawing the map, updating the elevation and saving the
track. If I switch to the map window or zoom, the screen remains yellow
and the "Drawing" label didn't disappeared. The speed reading was
changing but the elevation was fixed. As I could check later, there were
no track logging in that part.
When I moved the cursor in the map window, there was no cursor on the
screen, but I could see the coordinates for a while. Then, latitude went
to "N 0º 0.000m" and a distance from my position of about 4700km.
Switching on/off the unit didn't solved the problem. As soon as I tried
to redraw the map, again the same problem.
Switching off the Metroguide map and leaving the World map or basemap
alone solved the problem, but when I reactivated the Metroguide map,
freeze again... I could save two waypoints of the affected zone so I can
tell you the coordinates if you want. One was taken in the "go" trip and
the other in the "go back" trip.
The problem was automatically solved then I leaved the affected area...
any effort to reproduce the problem only moving the map to see the
affected area was useless... the problem only appeared when I was really
in that place.
* Another bug: Elevation in the waypoint. Maybe this is not a bug?
When making a waypoint, the elevation value is not what is shown in the
elevation field of the map. Instead, a near value appeared, and the
difference between the real and the shown value was varying.
Doing some experiments and checking the "GPS elevation" vs "Barometric
elevation", I think that the average elevation is put in the waypoints.
Also, derived from this, when averaging a waypoint, the elevation is
also averaged but ONLY from GPS Elevation data and not from the
barometric altimeter.
*Another "cosmetic" bug: in the elevation with time or pressure graph
(the green one) there is a zoom range badly labelled. When you select 6h
with the rocket, there are four divisions of 1h each (only 4 hours in
total and not 6h). But if you move the cursor from one mark to another,
the time changes 1.5h, so the "1h per mark" label is wrong.
*Other bug: In the track elevation profile (when you select it from a
saved track) if you change the zoom ranges, the elevation zoom range
will not be reduced. That is.. if you make the graph more and more flat
(moving the rocket up) you cannot make it sharp again moving the rocket
down. The scale seems to change but the graph remains the same. You have
to use the zoom bottons to change the elevation zoom range.
And finally another bug/feature?. With long tracks (mine used 85% of the
memory, over 1000km of tracks) the oldest ones were not drawn in the
map. So when I came back from my trip, by the same road, I could not see
the dotted line of the other trip, even saving it.
Well, I hope that this long email was useful for you and I really sorry
my bad English.
Any comment will be appreciated.
Best regards.
- Next message: Karl Pollak: "Re: BBC - Europe presses ahead on sat-nav"
- Previous message: Gus: "Re: Garmin 76S Won't Aquire Satelites"
- Next in thread: GSV Three Minds in a Can: "Re: My comments about the etrex Vista C"
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