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Cellular forums Home > Archive > Garmin GPS > October 2005 > Garmin 60CS Altimeter
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Garmin 60CS Altimeter
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| Tom Hemp 2005-10-18, 11:48 pm |
| I have been using the 60CS for about a year now and I am still confused on
how the altimeter works. I use the 60CS mainly for kayaking on flat water
lakes, So, prior to a trip I calibrate the 60CS altimeter at home because I
know what altitude my house sits at. When I get to the lake the altitude
looks pretty close based on the boat ramp sign that shows the base water
level. I usually kayak around and hike some and then return saving a track
of the trip. When I get back and down load the track, the altitude plot is
usually off significantly by the time I return to the boat ramp I started
from. When I get home the altimeter is totally off from what I set it at to
start. So, anyone know what could be going on here? I am at the latest
version of firmware for the 60CS.
Here are some other basic comments on the 60CS:
1.) No way to delete tracks, waypoints, etc on the 60CS from Mapsource.
This is a real pain, as I accumulate a slew of waypoints and tracks over
time and I have to remove them using the 60CS keypad which is slow as heck.
2.) I have the compass turned off till I need it. Just hold down the Page
button till it activates. Saves battery life.
3.) Always save a track after you complete a trip of any kind. Even with
tracking turned off you will lose the local track if the 60CS is left on, on
the way home or whatever.
4.) I like this site on making your own maps: http://rwsmaps.griffel.se/
Very technical but covers about everything.
5.) I use Garmin's City Select V6 and Fishing Hot Spots East Coast. You can
have both downloaded on the 60CS, just remember to turn off the City Select
V6 when on a lake by pressing menu on the map screen and selecting map
setup.
6.)Purchase the auto navigation kit for the 60CS, gives you City Select and
a nice mount for the car with power cord. I bought an external antenna but
have never used it.
7.) I have found many errors in the City Select maps. However, if you goto:
http://www.navteq.com/ and post the errors they do get fixed. I did a few
for V6 and V7 of City Select shows the changes. I know Garmin has to
protect the maps with a locking code, but it would be real nice if Mapsource
could make a road disappear. I am on various back roads around lakes and
some roads are submerged. So, when I ask to get me somewhere else on the
lake it will always make the mistake of taking me over the submerged road. I
want to delete that road from the route calculation.
8.)There is no voice on the 60CS for auto navigation. I thought there was
when I purchased the 60CS auto navigation kit on the power adapter.
9.)I have been very unlucky on using the search feature for addresses and
such. It is so picky on street names, capitalization, etc.
10.)When I ask for the closest McDonalds on a route that I am following it
usually takes me to the nearest one, which most of the time you have already
passed. Turning back is usually painful, so having some way to only show
what is on your route that you have not passed yet would be nice.
11.)I bought a screen
protector(http:
//www.boxwave.com/produ...ystal/index.htm). The
60CS is really rugged, but the screen can take a beating they way I use it
in the boat. I have to tether it to the boat also as it does not float.
There is a nice clip point at the top of the unit.
12.)I bought a camera case to hold all the stuff and the GPS. I looked at
Garmin's but it is very simple.
13) And finally do not expect Auto Navigation to be failsafe, as it usually
is not. You must get used to using it as a tool and not as the bible,
otherwise you will be taking some side trips that do not make sense. In
other words, you have to look at what it is telling you to do and make a
judgement is this reasonable.
Tom
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| George@eprintshoppe.com 2005-10-19, 2:48 am |
| Could it be the barometric pressure had changed while you were on the
water? That will make the altitude appear to be different. When
flying, I remember I had to constantly get the official barometric
pressure in my flight area so my readings would be correct.
FWIW, the satellite rendering of altitude is a lot less trouble in the
long run.
TexGEOas
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| richo@mcn.org 2005-10-19, 2:48 am |
| Tom Hemp wrote:
> Here are some other basic comments on the 60CS:
>
> 1.) No way to delete tracks, waypoints, etc on the 60CS from Mapsource.
> This is a real pain, as I accumulate a slew of waypoints and tracks over
> time and I have to remove them using the 60CS keypad which is slow as heck.
Why not just go to the Trip Computer screen > menu > Reset > Delete All
waypoints? After having saved any you want to keep to your computer of
course.
Rich Owings
http://www.MakeYourOwnMaps.com/
http://www.GPStracklog.com/
"We were desert mystics, my friends and I, poring over our maps as
others do their holy books." - Edward Abbey
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| David Lee 2005-10-19, 5:48 pm |
| Tom Hemp wrote ...
>I have been using the 60CS for about a year now and I am still confused on
>how the altimeter works. I use the 60CS mainly for kayaking on flat water
>lakes, So, prior to a trip I calibrate the 60CS altimeter at home because
>I know what altitude my house sits at. When I get to the lake the altitude
>looks pretty close based on the boat ramp sign that shows the base water
>level. I usually kayak around and hike some and then return saving a track
>of the trip. When I get back and down load the track, the altitude plot is
>usually off significantly by the time I return to the boat ramp I started
>from. When I get home the altimeter is totally off from what I set it at
>to start. So, anyone know what could be going on here? I am at the latest
>version of firmware for the 60CS.
Vertical accuracy of a recreational quality GPS fix is very inaccurate
(worse than the horizontal accuracy due to considerations of satellite
geometry) so your GPS receiver uses an aneroid barometer to measure the air
pressure. This will give you an extremely accurate measurement of altitude
provided that you have properly calibrated for the local air pressure
variation due to current weather conditions. However if the air pressure
changes due to a change in local weather conditions or because you have
moved to a location a significant distance from where you calibrated the
barometer, then the altitude measurement can exhibit large errors. To
correct for this (and for times when you have no way of calibrating
manually) your receiver has an Auto Calibration feature that basically
averages the GPS height data over a long period and gradually corrects for
the local barometric pressure. After a sufficiently long period of time you
should have very accurate altitude readings, provided that the local
pressure isn't varying too rapidly.
What's happening in your case is that you are calibrating the height at home
and then driving rapidly a significant distance to the lake so that the
calibration hasn't had enough time to stabilize when you arrive. As you
kayak around the lake at a leisurely pace the accuracy of the height
calibration will normally improve so that you should have a much more
accurate (and hence different) estimate of the altitude of the boat ramp
when you return. You then return home after being away for several hours so
not only is the local barometric pressure likely to be different from that
at the lake but it will also probably have changed, perhaps greatly, from
what it was when you left earlier in the day and so you may see a very
different estimate of altitude. You would need to leave your GPS receiver
on for a significant period of time to stabilize its barometer calibration
before you could rely on the altitude reading again.
Hope that's clear enough!
BTW you should be able to turn off auto calibration and get instantly
accurate altitude readings provided that you can enter an accurate
calibration manually (System menu/Altmeter on the Vista). However if you do
this then remember that the GPSR will NOT compensate for subsequent drifts
in local barometric pressure, as the weather changes, so that height
accuracy may degrade significantly with time.
David
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| David Lee wrote:
> Vertical accuracy of a recreational quality GPS fix is very inaccurate
> (worse than the horizontal accuracy due to considerations of satellite
> geometry) [...]
I don't think the vertical error is inherently any worse than the
horizontal. I think that we are much more aware of altitude uncertainty
because a) we don't expect it, especially on the water, and b) the units
of measurement tend to highlight or hide the magnitude of variation -- a
lateral displacement of .002 minutes of longitude is roughly the same as
a 10-12-foot elevation change, but you don't usually think of
terrestrial distances in terms of angular distance, and look at that
changing least-significant-digit as measurement uncertainty.
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| David Lee 2005-10-20, 11:48 pm |
| Don wrote...
> David Lee wrote:
>
> I don't think the vertical error is inherently any worse than the
> horizontal.
My understanding is that vertical accuracy is worse than horizontal by about
a factor of two to three due to the average geometry of satellite positions.
David
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| Tom Hemp 2005-10-20, 11:48 pm |
| Thanks for all the discussion. Just turned off 'Auto Calibration' and will
see what that does on a trip. Never thought of deleting all waypoints and
then downloading them again. Thanks, Tom
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| roybassist@yahoo.com 2005-10-24, 2:48 am |
|
Tom Hemp wrote:
> I have been using the 60CS for about a year now and I am still confused on
> how the altimeter works. I use the 60CS mainly for kayaking on flat water
> lakes, So, prior to a trip I calibrate the 60CS altimeter at home because I
> know what altitude my house sits at. When I get to the lake the altitude
> looks pretty close based on the boat ramp sign that shows the base water
> level. I usually kayak around and hike some and then return saving a track
> of the trip. When I get back and down load the track, the altitude plot is
> usually off significantly by the time I return to the boat ramp I started
> from. When I get home the altimeter is totally off from what I set it at to
> start. So, anyone know what could be going on here? I am at the latest
> version of firmware for the 60CS.
Do you have the GPS on while driving? Your answer to this question
would provide a really important clue. Roughly how far do you drive?
Are the trips you refer to day trips, or multi-day trips?
> I bought an external antenna but
> have never used it.
Along with my antenna, I bought a suction cup window mount. I don't
normally use it when I can put my receiver on the dash (in my car or a
rental car); but in airplanes, trains, busses, and other people's cars
when I can't ride in the front seat, I stick the mount with the Gilsson
to a window and I'm in business. This lets me hold the receiver where
it's easiest to see the screen, while getting good satellite reception.
> When I ask for the closest McDonalds on a route that I am following it
> usually takes me to the nearest one, which most of the time you have already
> passed. Turning back is usually painful, so having some way to only show
> what is on your route that you have not passed yet would be nice.
I agree with you, but it may never happen. Next best thing is to check
whether the distance is increasing or decreasing before you select "Go
To". You can also look at the bearing and generally tell whether it's
in front of you or behind you.
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