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GPS accuracy indoors

I recently purchased the FR645 and have been using it primarily for outdoor running. Today I decided to go for a short walk to a local store using the outdoor walk exercise. The device registered 1 mile when I was about 50 feet from the main entrance, which was accurate. Once inside the store, and not moving for a period of time, I noted the auto pause feature did not activate (I know I had auto-pause turned on because it worked when I stopped to cross a busy street). After exiting the store several minutes later I glanced down at the watch and saw the distance was now reading 1.40 miles. There is no way I covered 0.40 miles in the short time I was inside the store. Upon returning home and looking at the GPS track on the computer I saw a strange zig zag pattern inside the store with a flat cadence reading for that same period of time.

I've done this same walk with the FR620 and never saw this type of behavior while inside this store.

Anyone have a similar experience or know what could have caused this behavior? Rather disappointed to be experiencing this with a device at this price point. Granted I haven't noticed any GPS discrepancies with the 645 during my outdoor runs but this experience causes me to call into question its overall accuracy.

Thanks in advance for any help.

0 Former Member over 7 years ago

You were inside a building and you're questioning the GPS accuracy?

https://support.garmin.com/en-US/?fa...acy&textPage=3

https://itstillworks.com/doesnt-gps-...ing-18659.html

0 skiman1818 over 7 years ago

As I stated, did not experience this issue doing this same route going inside of this same building using the FR620 on numerous occasions. This is only my 2nd Garmin product so I don't have a lot of experience using these devices. Considering the FR645 is a newer model I don't think it's unreasonable to be surprised when an issue like this crops up.

My understanding of a forum is to assist those who have questions or concerns, not talk down to them.

Thanks anyway for your help.

0 Former Member over 7 years ago

I think it's a fair reply since GPS is an outdoor function, so what happens indoor is essentially irrelevant.

What's your experience like with it outdoors? That's all that matters.

I initially had issues, with tracks that went wonky whenever the signal got a bit weak (not seen in my 735XT track). But the distance and pace info was generally on the money. I discovered it was because i was wearing the watch on the inside of my forearm, and this must have blocked enough of the sky while running to degrade the track when the signal wasn't strong. Once i moved it back to the top of my wrist the tracks have been great.

(Note i wore it on the inside of my forearm to get a stronger HR signal, which the 735XT needed. But i've found the 645 to be amazingly accurate in this respect, no matter where i wear it. So all is good.)

0 Nighthawk700 over 7 years ago

A while back on the suggestion section of the 235 part of the forum, I said I wish there was a way to temporarily stop the GPS from recording/moving location when I go indoors. Whether I'm in a port-o-pot or in a store, my track sometimes goes wild. I know I can pause the run, but I want to keep the clock and other stats going, just tell it I'm not moving anywhere while, um, otherwise occupied.

0 Former Member over 7 years ago

My understanding of a forum is to assist those who have questions or concerns, not talk down to them.

I have no idea why you feel I was talking down to you. You posted a question that is covered in your manual, on the Garmin Support website, in these forums and what the overwhelming majority of people would consider common knowledge. My 935 displays on it's screen to move away from buildings, etc when trying to acquire a GPS fix. I assume the 645 does also? Because of this I posted my reply as a question for clarification. You did not state your 620 worked numerous times at that location in your original post. You simply wrote it worked in the past. Anyone reading your post has no idea if that was once or a hundred times. You say you now question the overall accuracy of the 645's GPS. That may be a bit premature based on one trip with the your new watch. I provided you with links to assist and inform you. How is this not helping with your questions or concerns? It's your choice to utilize that information or not.

0 skiman1818 over 7 years ago

Thanks for the replies. I do understand GPS will not function as well indoors as outdoors. What I didn't expect was the addition of nearly a half mile to my walk for the brief time I was inside. As you mentioned Nighthawk700, this would also be a concern for me running a race. I disable auto pause to keep an accurate overall race time yet I don't want the other stats to suffer should I go under a bridge or have to use a bathroom.

Sorry if this seemed like an ignorant question on my part but the only point of reference I have is my FR620 which did not behave this way. If I was indoors and standing still with auto pause enabled it would engage and disengage a few times screwing up my pace time a little but I never noticed any strange tracking behavior. Potentially having this much distance added to a run should I need to make a brief stop indoors is a concern for me.

0 Former Member over 7 years ago

The tough part about GPS indoors with wearable devices is the experience is likely to be very inconsistent due to many factors. The watch isn't able to know if you are indoors or outdoors it just knows if it has a GPS signal or not. Most often, the GPS signal will be interrupted when indoors, but there are situations where a weak GPS signal will be maintained. If the are enough satellites in the right position in the sky or enough windows in a particular building, a weak signal may be able to connect to the watch and cause extra distance to be tracked. Because it is a weak/degraded signal there is a higher chance of inaccurate GPS data, which could cause the Auto Pause to not pause the timer because the watch thinks it is still moving due to the inaccurate GPS data.

It is recommended that anytime you enter a building during a run, that you manually pause the timer to ensure that the device does not maintain a poor GPS signal.

0 skiman1818 over 7 years ago

Thank you for the explanation Garmin-Joey.