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Elevation issues with Garmin Forerunner 745

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Elevation issues with Garmin Forerunner 745

Old 01-15-23, 05:00 PM
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Elevation issues with Garmin Forerunner 745

Hi. Can anyone explain what's going on with my Garmin 745 and the recording of elevation? Take a look at this from my most recent run:



This was an out and back run. And I did not suddenly climb a mountain at the approx 20 min mark. I have no idea why the elevation jumped from approx 0m to 200m.

I am seeing this type of elevation error/correction happening on my runs regularly. At the 20 ~ 30min mark the elevation jumps up like this. Any thoughts on why I am seeing this? Is anyone else experiencing the same with their watches or bike computers? Thank you.
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Old 01-16-23, 08:54 AM
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Something happened to suddenly make it do a correction. Do you have to know the exact details of why?
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Old 01-16-23, 09:13 AM
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Does the watch have a barometric sensor ?. Make sure the port isnt clogged amd otherwise see if theres a configuration for the altitude.

In general, elevation determined by GPS alone is widely inaccurate. So expect wonky numbers,
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Old 01-16-23, 05:07 PM
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If you have not used it for a while and the stored data on the satellite orbits is out of date, as you ride and as different satellites are used, when the unit changes which satellites it is using, that might be what is happening.

I have seen that on my own GPS occasionally but only if the GPS has not been used for several weeks. It should take something like 10 to 20 minutes for the GPS to download new orbit information if you have a clear view of the sky, no clouds, no trees. Clouds or trees may make it take longer to update the GPS with orbit information.

Try turning on your GPS a half hour before you start your ride where the GPS has clear view of sky and see if that solves it.

I am not familiar with that GPS, if it is a really small one with small antennae, that could slow down how fast it loads orbit info and it might also mean that it gets location data from fewer satellites.

Keep in mind that the satellites are many thousands of miles away and they do not have a lot of electric power to transmit a signal.

Also, elevation data from a GPS has about twice the amount of error that it has for horizontal location, so elevation data is not really that great.
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Old 01-18-23, 09:44 PM
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I use my watch every day and the GPS gets used at least three times a week. Regarding the barometric sensor, that is a good question. I do not know. I will have to do some googling around.

I did find something out that was interesting the other night though. I also run with a running dynamics pod to capture running dynamics. Sometimes the watch recognizes the pod right away and sometimes not. Anyway. Last night the running pod was recognized at the start of the run. And wouldn't you know it? There was no sudden jump in elevation. I am starting to wonder if the running dynamics pod, which captures ground contact time, is having some sort of impact on the elevation profile readings. I will do some more experimenting with the running pod to see it the pod is having any impact.
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Old 01-19-23, 09:45 AM
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Originally Posted by NoWhammies
I use my watch every day and the GPS gets used at least three times a week. Regarding the barometric sensor, that is a good question. I do not know. I will have to do some googling around.

I did find something out that was interesting the other night though. I also run with a running dynamics pod to capture running dynamics. Sometimes the watch recognizes the pod right away and sometimes not. Anyway. Last night the running pod was recognized at the start of the run. And wouldn't you know it? There was no sudden jump in elevation. I am starting to wonder if the running dynamics pod, which captures ground contact time, is having some sort of impact on the elevation profile readings. I will do some more experimenting with the running pod to see it the pod is having any impact.
Does the running pod generate its own elevation data ?. Maybe that data sometimes gets sent to the watch as accurate data, and on occasion if the pod is not connected, the watch generates its own incorrect data ?. Do some runs with no pod, see what the elevation info looks like, if its incorrect, work to fix that.
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Old 01-20-23, 10:38 PM
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Steve B. I do not think the running pod generates its own elevation data. I think it only calculates power, stride length, and some other metrics. Funny enough I ran tonight and made sure the watch and run pod were connected. Again, no problem with the elevation. I will give a run a go without the pod and see if the elevation problem comes back again. Thank you.
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Old 01-22-23, 09:11 AM
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If it’s a GPS issue, the track would show it.

The 745 has a barometer and you can switch it between measuring altitude and pressure (for weather without climbing).

It’s possible that the GPS was off and it was using the wrong location to “calibrate” the barometer at first. Then when the GPS kicked-in with the right location, the baseline for the barometer changed.

As far as I know, this “calibration” requires explicitly saving points and indicating the known elevation (it’s a deliberate process that people would likely remember doing). Most people don’t do this (it’s extra work). It also doesn’t effect gain numbers anyway. Which is what most people are interested in (people don’t usually care about absolute altitude).

Again, the track would show issues with GPS.

The barometers can take some time to adjust to ambient pressure but that wouldn’t cause an abrupt change.

Last edited by njkayaker; 01-23-23 at 07:44 AM.
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Old 01-22-23, 09:18 AM
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Originally Posted by NoWhammies
I use my watch every day and the GPS gets used at least three times a week. Regarding the barometric sensor, that is a good question. I do not know. I will have to do some googling around.

I did find something out that was interesting the other night though. I also run with a running dynamics pod to capture running dynamics. Sometimes the watch recognizes the pod right away and sometimes not. Anyway. Last night the running pod was recognized at the start of the run. And wouldn't you know it? There was no sudden jump in elevation. I am starting to wonder if the running dynamics pod, which captures ground contact time, is having some sort of impact on the elevation profile readings. I will do some more experimenting with the running pod to see it the pod is having any impact.

It’s very unlikely the pod has any affect on the elevation.

It’s not “interesting”. It’s a coincidence.
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Old 01-22-23, 10:39 PM
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Yeah, something is definitely off with my watch. Here is the elevation profile from my run today:



Again. This was an out and back route. So the major drop in elevation should not have taken place.

njkayaker I am fairly confident that my GPS was working fine and did not kick into place at the 40 min mark of my run. Now comparing this run with the run I did on Friday, granted it was a shorter and different route:




So I am not sure what is going on here. If I find 30mins in my day, I will give Garmin a call and see what they can tell me. I have not done any changes to base settings of my watch, so I would be surprised if the barometer was having an impact. But then again, what do I know? I could be wrong. Maybe some sort of update was applied without my knowledge and some default settings were changed.
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Old 01-23-23, 06:35 AM
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Originally Posted by NoWhammies
...



...
Yeah, something wrong if you were not below MSL. I am assuming you were not in death valley or some other place that has negative elevation.

And you were not SCUBA diving, as the water would have blocked the GPS data.

I have occasionally had an odd GPS elevation for a short time of maybe a few minutes if I had not used my GPS for a while (as I noted above) but in this case it is showing you at a negative elevation for over an hour.
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Old 01-23-23, 07:30 AM
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Originally Posted by NoWhammies

njkayaker I am fairly confident that my GPS was working fine and did not kick into place at the 40 min mark of my run. Now comparing this run with the run I did on Friday, granted it was a shorter and different route:
I wasn’t suggesting that the GPS might be a problem.

Other people were.

I was just saying looking at the track would be the easy way of seeing if GPS was a problem. Any GPS issue that would affect the barometer in this way would be really obvious.

Presumably, you looked at the track and didn’t see anything unusual.

So, actually, other people suggesting it might be the GPS is a bit odd/pointless.

(I was actually suggesting it wouldn’t be the GPS because, presumably, you saw the track and didn’t see anything unusual.)

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Old 01-27-23, 10:06 PM
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Tourist in MSN Yeah, something is definitely off. I use my watch for running three or four times a week so it is int like the GPS is sitting unused. Tonight, for example, there were no issues with the GPS. All I can think of what happened is that the GPS had a full moment to lock onto satellites before starting my run. But, for that run above, the GPS had locked onto satellites before I started my run. Or at least the bar at the top of my watch had turned from red to green, indicating satellite lock.

njkayaker Apologies for my error.

Here's a question. Does anyone know if there is a way to reset the GPS without resetting the whole watch? Maybe I will take a look at the run profile and see what the GPS setting is. Perhaps there is a clue in there, somewhere.
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Old 01-27-23, 10:24 PM
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Originally Posted by NoWhammies
...
Here's a question. Does anyone know if there is a way to reset the GPS without resetting the whole watch? Maybe I will take a look at the run profile and see what the GPS setting is. Perhaps there is a clue in there, somewhere.
I do not know, but if there is a way it might not help you fix things. Keep in mind that the satellites are moving all the time, and the specific satellites your GPS is using to get a fix will change over time. My point is that I doubt that there is some bad orbit data in your GPS but even if there is, it should be overwritten in the near future. It is unlikely that a reset is needed.
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Old 01-28-23, 07:41 AM
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Originally Posted by NoWhammies

Here's a question. Does anyone know if there is a way to reset the GPS without resetting the whole watch? Maybe I will take a look at the run profile and see what the GPS setting is. Perhaps there is a clue in there, somewhere.
???

Why do you want to reset the GPS?

You haven’t indicated a problem with the GPS. It should be obvious if there’s an issue with the GPS.
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Old 01-28-23, 04:36 PM
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njkayaker just like rebooting your computer can fix computer glitches, I am thinking that resetting the GPS will fix whatever is wrong with my elevation issues.
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Old 01-28-23, 08:38 PM
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Originally Posted by NoWhammies
njkayaker just like rebooting your computer can fix computer glitches, I am thinking that resetting the GPS will fix whatever is wrong with my elevation issues.
Doesn’t make sense.

Rebooting a computer is like resetting the “whole watch”.

“GPS” is one part of the “whole watch”. The barometer (elevation) is a different part of the “whole watch”.

Resetting the GPS part wouldn’t do anything for the barometer part.

in any case, there isn’t a way to reset either part.

Anyway, are you having repeated problems with the elevation or was it a one-time thing?
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Old 01-28-23, 11:06 PM
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Its a reasonable question, just wants to know if resetting the part of the watch that receives and processes the GPS signal would reset it, without the need to do a reset of all the data as well as configuration settings on the watch. My only answer is I've never seen that on a Garmin watch. I know on my Instinct, when I power down, then power up again, I need to manually acquire the GPS system in order to get position (AFAIK).
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Old 01-29-23, 06:47 AM
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Originally Posted by Steve B.
Its a reasonable question, just wants to know if resetting the part of the watch that receives and processes the GPS signal would reset it, without the need to do a reset of all the data as well as configuration settings on the watch.
???


He’s talking about a problem with elevation (on a watch with a barometer).

He’s not having any issue with the GPS.

He wants to reset the GPS to fix the elevation.

What do you think resetting the GPS is going to do?


Originally Posted by Steve B.
It know on my Instinct, when I power down, then power up again, I need to manually acquire the GPS system in order to get position (AFAIK).
???

”Manually acquire”?

Don’t these devices do that automatically?

This (automatic) process is normal (for devices that are turned on before use). So, it really isn’t something that would typically be considered “resetting”.

The watch is doing the same thing without being turned off after being indoors for awhile anyway.

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Old 01-29-23, 02:49 PM
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If you power up the watch when indoors, it cannot acquire a GPS signal, thus when you go outdoors, its not magically going looking, it only does that on boot, you thus press and hold the upper right button (Instinct 2 Solar) to get a GPS signal. I always power down at night if not using to prolong battery life.

The OP has been concerned that a problem with how his watch receives GPS is maybe causing the weird elevation issues. Thus I understand he does not desire to do a complete factory reset just to fix any potential GPS issue, as doing so resets his configuration and history.
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Old 01-29-23, 03:01 PM
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Originally Posted by Steve B.
The OP has been concerned that a problem with how his watch receives GPS is maybe causing the weird elevation issues.
This makes no sense.

The OP is grasping at straws.

It’s not going to fix his problem.

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Old 01-29-23, 03:45 PM
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Whelp. Amazing what a little google searching can turn up.

Looks like I am not the only one experiencing this issue. Seems like the issue is affecting multiple people and is the result of some bad software. Not sure what the end result will be. Looks like some people on the Garmin forums have called in to Garmin support so I will do the same and my name to the list of complaints.

Thanks to everyone for chiming in.
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Old 01-29-23, 05:39 PM
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Originally Posted by NoWhammies
Whelp. Amazing what a little google searching can turn up.

Looks like I am not the only one experiencing this issue. Seems like the issue is affecting multiple people and is the result of some bad software. Not sure what the end result will be. Looks like some people on the Garmin forums have called in to Garmin support so I will do the same and my name to the list of complaints.

Thanks to everyone for chiming in.
It's really one of the first things you should do when you have issues. How will Garmin know there is really an issue they need to solve if enough people don't call them about the same issue?

Even if your product isn't in warranty any more.
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Old 02-05-23, 03:51 PM
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Just to close the circle on this a little bit. I spoke with Garmin customer service and they offered to replace my watch. I took them up on the offer. Comments in the threads have indicated that a new watch did not solve the issue for some people. But I figured what the heck have I got to lose? Hopefully the new watch will solve my problems.

Great customer service from Garmin BTW. Responsive and took the time to walk me through various trouble shooting steps. Nice and friendly too.
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