Garmin GPSMAP 60Csx Quirks?

[MunkeyTX]

I live right on the Gulf, and I've calibrated my altimeter by placing it right at sea level and setting the known altitude to '0'. Immediately after calibration, the GPSr reports somewhat accurate altitude readings, but after more than 15 - 20 minutes, it goes wonky. In places where it reported altitudes of 30 to 40ft, it will read -10 to -120ft! I only noticed this while looking at my track log in MapSource. My old GPSIII+ was almost dead on at determining altitude...so what's up with my Csx?

 

Also, I've noticed that my Csx will report movement, when I'm dead still, and have been sitting dead still for quite some time. I noticed this when I left the Csx in my truck while the engine warmed up. I had reset the trip odo on the Csx, and gone back inside to get something. When I came out again, it had reported that I moved .08 miles! I've also noticed that at long stoplights, it'll suddenly tick off that my speed is .02 mph. Again, my old GPSIII+ was always spot on on speeds and odo readings.

 

I love my Csx, it's more GPS than I could ever need (consider I finally upgraded from my GPSIII+), but these little quirks get under my skin!

 

Any help?

[echo_26]

...I believe its' the nature of the Sirf receiver to roam a bit when still..It's been talked about on here in the past...I have the same unit and notice the same behavior..

Edited January 24, 2008 by echo_26

[+rstickle]

I was trying something for a different reason and left both a Vista HCx and a 60 CSx in a window sill to check movement (Drift?) for an hour. The Vista "moved" 193 meters, and the 60 "moved" 202 meters during the timed hour. Don't know if that will help you any. I wasn't checking altitude, but any change in barometric pressure will cause movement.

 

Rick

[+blackprince]

I wasn't checking altitude, but any change in barometric pressure will cause movement.

 

And change in satellite geometery, temperature, ionospheric conditions....

Edited January 24, 2008 by blackprince

[nathantw]

I live right on the Gulf, and I've calibrated my altimeter by placing it right at sea level and setting the known altitude to '0'. Immediately after calibration, the GPSr reports somewhat accurate altitude readings, but after more than 15 - 20 minutes, it goes wonky. In places where it reported altitudes of 30 to 40ft, it will read -10 to -120ft! I only noticed this while looking at my track log in MapSource. My old GPSIII+ was almost dead on at determining altitude...so what's up with my Csx?

 

I don't know if this will help you or not, but I have a Tissot T-Touch watch that displays the altimeter. When I set my watch to match the 60CSx altimeter they both basically stay at the same altitude, whether it's 20 feet above/below or hundreds of feet above/below. I think the air pressure has a lot to do with what's being displayed.

[wildgoose007]

Wait till you bring the 60CSX on a plane trip. The elevation shown is -X ft, based on the cabin pressure. There's no way to change it to the GPS elevation so you can monitor the plane's elevation continuously. This has been reported numerous times to Garmin and the request has fallen on deaf ears. If this bothers you, please contact Garmin and let them know. I even kindly pointed out to them that they dont' need to disable the alti-meter, which they said is very hard to do, but just add a data field called gps-elevation. This should be trivial to do.

[NewZealand]

Wait till you bring the 60CSX on a plane trip. The elevation shown is -X ft, based on the cabin pressure. There's no way to change it to the GPS elevation so you can monitor the plane's elevation continuously. This has been reported numerous times to Garmin and the request has fallen on deaf ears. If this bothers you, please contact Garmin and let them know. I even kindly pointed out to them that they dont' need to disable the alti-meter, which they said is very hard to do, but just add a data field called gps-elevation. This should be trivial to do.

On the Odometer it's right, you can only see the Altimeter elevation.

But for the tracklog you can select between Altimeter elevation and GPS elevation.

Go to the Altimeter config and select "fix elevation" instead of "variable elevation", and the GPS elevation will be recorded in the track log.

[+hogrod]

On the 60csx you can view the gps elevation from the satellite page by pressing the menu key and selecting GPS elevation.

[+hogrod]

I live right on the Gulf, and I've calibrated my altimeter by placing it right at sea level and setting the known altitude to '0'. Immediately after calibration, the GPSr reports somewhat accurate altitude readings, but after more than 15 - 20 minutes, it goes wonky. In places where it reported altitudes of 30 to 40ft, it will read -10 to -120ft!

 

What you are describing sounds like you have auto calibration turned on, this setting uses the GPS elevation(what its computing from the satellites) to help get an accurate barometric reading quicker without needing to know the local pressure or elevation. Since the gps elevation can fluctuate +/-200ft it can actually pull the altimeter out of whack pretty quick. On the flip side if you didn't know the current local pressure or elevation this setting does actually make the unit display a more accurate elevation over just a short period.

 

You can change this setting here: main menu, setup, altimeter

[+apersson850]

The 60 CSx can only display a snapshot of the GPS elevation. If you want an update, you have to close the window and open it again.

The Colorado can display the current GPS-derived elevation continuously, if you look at the satellite screen.

[+Prime Suspect]

Wait till you bring the 60CSX on a plane trip. The elevation shown is -X ft, based on the cabin pressure. There's no way to change it to the GPS elevation so you can monitor the plane's elevation continuously.

You need to monitor the plane's elevation continuously?

 

IMO, it behaves exactly as a outdoors/hiking GPS should behave.

[pratzert]

AM I undeerstanding this correctly ?

 

I have a 76CSx and with this particular GPSr, it dispays the elevation based on the relative/ambient barometric pressure ?

 

Do you have to enter some sort of baseline from a known point of elevation ?

 

This is pretty crazy if that's how it really works. Barometric pressure takes huge swings in both directions with passing low and high pressure centers.

 

Tim

Edited January 31, 2008 by pratzert

[+stingray67]

AM I undeerstanding this correctly ?

 

I have a 76CSx and weith this particular GPSr, it dispays the elevation based on the relative/ambient barometric pressure ?

 

Do you have to enter some sort of baseline from a known point of elevation ?

 

This is pretty crazy if that how it really works. Barometric pressure takes huge swings in both directions with passing low and high pressure centers.

 

Tim

 

My 60Csx is pretty accurate i'd say about plus or minus 5m on any one reading. Velocity will change as signals are reflected and deflected through ever changing atmosphereic conditions. However, these will usually be very slight. As with pressure, as far as i know the 60Csx takes many readings to determine the altitude through barometric pressure. You say there a swings in pressure.. well of course but these are averaged out to give a faily accurate reading. Swings wont usually be that big unless u so happen to wander into a tornado!

Edited January 31, 2008 by stingray67

[roybassist]

I have a 76CSx and weith this particular GPSr, it dispays the elevation based on the relative/ambient barometric pressure ?

Yup.

 

Do you have to enter some sort of baseline from a known point of elevation ?

Yes and no. You can:

1) Calibrate to the elevation where you are, if you know it,

2) Calibrate to the barometric pressure where you are, if you know it (this is the sea-level adjusted barometric pressure reported by weather stations everywhere; no fancy calculations required. A weather station within 25 miles is plenty close for this purpose)

3) Calibrate to the current GPS elevation. In this case you are at least as well off as those who don't have barometric sensors, since GPS elevation is all that their receiver can give them. Unfortunately, GPS elevation is subject to relatively large errors, and it changes constantly as satellite geometry changes; but it is pretty good as a starting point for autocalibration (see below) if you don't know your current elevation or barometric pressure, or

4) Calibrate to nothing, and eventually (30 minutes to an hour in typical situations) autocalibration (if you have it turned on) will still get you pretty close to a "real" elevation.

 

This is pretty crazy if that how it really works. Barometric pressure takes huge swings in both directions with passing low and high pressure centers.

That isn't a problem if you turn on autocalibration. Autocalibration compares the difference between the elevation determined by the barometric sensor with a somewhat long-term average of GPS elevation, and calibrates the barometric elevation to minimize the difference. Over a period of time (don't as me how long), the average GPS elevation is relatively accurate. By calibrating the barometric sensor to the average GPS elevation, the effects of pressure changes are compensated for. Automagically. It's very sophisticated, and it works very well. Mine corrected a deliberate miscalibration of 100 feet in about an hour. That's much faster than barometric pressure normally changes.

 

Amazingly, autocalibration seems to work well over the length of a day even when I turn my receiver on only occasionally to get a position fix and then turn it off again to save batteries. A fellow named Chris Malcolm once documented that the algorithm seems to have what he called a "fast catch-up mode" to handle this situation. Unfortunately, Mr. Malcolm's excellent web page on autocalibration is no longer where it once was, and I've been unable to find it elsewhere.

 

Of course, even the average of GPS elevation isn't perfect, so your receiver may still be off some, but it's pretty good, and definitely better than GPS elevation alone. The downside is that for periods of time that are short enough for the barometric pressure to be constant, autocalibration may actually reduce accuracy, as hogrod stated very well previously in response to the OP:

 

What you are describing sounds like you have auto calibration turned on, this setting uses the GPS elevation(what its computing from the satellites) to help get an accurate barometric reading quicker without needing to know the local pressure or elevation. Since the gps elevation can fluctuate +/-200ft it can actually pull the altimeter out of whack pretty quick. On the flip side if you didn't know the current local pressure or elevation this setting does actually make the unit display a more accurate elevation over just a short period.

[pratzert]

So it sounds as if the 76CSx has BOTH the ability to calulate the elevation based on actual GPS Satellite signals AND a Barometric sensor reading.

 

Further.... I gather it starts out using the GPS satellite signals to load an approximate elevation and then fine tunes or adjusts the elavation based on changes in the Barometric readings ?

 

I have the ability to turn the Auto-compensating feature using the Barometric pressure reading OFF.

 

In this case, I will only have the GPS elevation reading/calculation available to me ?

 

Is this correct ?

 

Thanks for sharing all your knowledge..... it helps tremendously.

 

Tim

Edited January 31, 2008 by pratzert

[roybassist]

So it sounds as if the 76CSx has BOTH the ability to calulate the elevation based on actual GPS Satellite signals AND a Barometric sensor reading.

Yes, but it can display only the barometric elevation as a continuously updating data field.

 

Further.... I gather it starts out using the GPS satellite signals to load an approximate elevation

Only if you specifically manually calibrate to GPS elevation. If you don't, it will start with the current barometric elevation, which will be affected by any pressure changes since you last had the unit turned on. If you want it to start with anything else, you have to calibrate it manually using one of the choices I listed in my previous post. You can calibrate manually by going to the altimeter page, pressing menu and selecting "Calibrate Altimeter". There are a couple of other ways to access the calibration screen, but they all take you to the same place.

 

and then fine tunes or adjusts the elavation based on changes in the Barometric readings ?

Only if you have autocalibration turned on.

 

I have the ability to turn the Auto-compensating feature using the Barometric pressure reading OFF.

Yes. MENU>MENU>Setup>Altimeter.

 

In this case, I will only have the GPS elevation reading/calculation available to me ?

 

Is this correct ?

No. Elevation displayed as a continuously updating data field will always be based on the barometric sensor. There is no other option. If you turn off autocalibration, the barometric sensor just won't be automatically corrected for changes in weather. If the sensor is initally calibrated to a known elevation, turning autocalibration off will usually be more accurate in the short term and less accurate in the long term.

 

The only way you can display GPS elevation on this receiver is to go to the Satellite page, press MENU and select "GPS Elevation". This gives you a snapshot of the GPS elevation at that moment. To get it to update, you must back out and do it again. Many have asked Garmin for years to offer GPS elevation as a data field choice, but Garmin has been unresponsive on this. This would be nice when traveling in a pressurized aircraft, but I can't think of any other reason to use it. When calibrated using the best data you have, even if it's GPS elevation, the barometric elevation will normally be more accurate than GPS elevation alone.

 

Of course, you have to use some common sense. The barometric altimeter works well in the gradually changing environment normally encountered in nature. If you open a car window on the highway, or make a big change in the setting of the ventilation fan while the windows are closed, you will see the elevation reading affected. But if you maintain those conditions long enough, autocalibration will do a reasonable job of adjusting for them.