heading accuracy without magnetic compass

Without a magnetic compass, the FR630 is often pretty useless for heading, unless you have the GPS activated such as recording an activity. GPS should only help with accuracy when you are actually moving. But I've noticed that with GPS activated, even stopping and just rotating in place, the heading still seems to remain pretty accurate. Rotate 180 degrees, and the heading adjust by close to 180 degrees. Do the watches without magnetic compass use accelerometers or something to track heading once they have been somehow calibrated via GPS and movement?

Is there any way to know if the heading is coming from GPS or a magnetic compass in my app? If it is using the accelerometer somehow, any suggestions on best practices as to how long/often I need to keep the GPS activated for reasonable results. In my app, I'm not using GPS for anything else so just a battery sink to keep it enabled.

tmk2 over 8 years ago

Are you sure the 630 lacks magnetic compass?

Simple experiment to make sure:
Don't move the watch, wait a little for the heading to settle, and then try moving a magnet around the watch. If you don't have a magnet lying around, even moving a smartphone close to the watch should give a slight response from the compass.

jim_m_58 over 8 years ago

If it's like the 23x, it does have a compass, but there may not be a way to calibrate it. Per the simulator, the 630 does have one (Sensor.Info.mag is there). If you always want to use it, you could just use Sensor.Info.mag directly.

From what I've seen, on devices with a mag compass and with GPS on, heading will come from the compass at low speeds (if you're stopped and looking at the watch for example), but then goes GPS based when you get moving. Without GPS, maybe it's confused at times as your wrist isn't pointed the way you're going much of the time, and it will be more vertical.

ekutter-dnu over 8 years ago

view 5000

OK, so it does have a magnetic compass. The magnet trick verified this. Thanks.

Interestingly enough, when I am out on the trails, it seems like it often times is accurate, but other times the heading seems somewhat random. Even when I'm really careful to hold it level in front of me.

What lead me to believe it didn't have a magnetic compass was that I've also had times here in my office with it sitting on my desk, where I just slowly spin it in place, the heading value doesn't change more than a few degrees (yes, I've converted from radians). As I sit here right now, it is properly going through the full 360 degrees.

I was also looking at the device list at https://developer.garmin.com/connect-iq/compatible-devices/ and it doesn't list a compass for the 630. But maybe that just means they don't provide a compass app. Specs on garmin's web page for the 630 also doesn't list a magnetic compass.

jim_m_58 over 8 years ago

It could also be that the compass can't be calibrated so maybe not that accurate), and there's also nothing native on the 630 to really see it. On other devices with a HW compass (the va-hr for example), there's a calibration step that is basically a figure 8, turning the watch over for 1/2 of it, so the process kind of takes the watch through 360 degrees.