A cautionary tale: don't trust your compass

StewartR

StewartR

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I posted this in 'Night and Astro Photography' but I think the lesson may be relevant to landscape photographers too.

Short version:
I was taking a shot where it was critical that I could take a compass bearing and line up the camera accordingly. (In my case I needed to know where the International Space Station would rise, but it can also happen if you need to know where the sun will rise.) I didn't have a proper compass with me and I relied on the compass in my phone. Unfortunately it turns out that the compass in my phone needs to be calibrated, so I didn't get the shot I was after.

Long version, with picture:
https://www.talkphotography.co.uk/threads/not-much-of-the-iss-and-a-cautionary-tale.646893/
 
To calibrate your phone compass you need to wave it around in a 3 dimensional figure of 8, there are a few diagrams on an internet near you. I did quite a bit of work on this a few years ago. The issue is that the magnetometer in your phone is quite close to a lot of electrics which have their own magnetic field which in itself wouldn’t be so bad but the current flow to other components varies, for example the phone module might start polling a tower and up its current consumption, this changes the local magnetic field. By rotating the phone through the earth’s magnetic field in 3 dimensions the current local maxima and minima can be found and these are taken as magnetic north/south. I found that putting the phone in flight mode and having as little as possible changing on the screen (i.e. avoid compass apps with fancy graphics) was the most reliable way to get a reasonable reading, even then it was only good to about 10 degrees repeatably.
 
I wanted a compass a couple of months ago, not for complex navigation, just so I knew which way I was facing when outdoors on a cloudy day. I opted for a 'cheap and cheerful', Chinese-made, military type compass with folding lid, as I figured it would stand up to being chucked in kit bags and coat pockets better than one of the clear plastic type ones. I had to laugh when it arrived and I checked it for accuracy though... it's the first compass I've ever owned that pointed South! :confused: Yes, really! Fortunately I bought it via a well-known online retailer, so sending it back was free and the replacement actually seems quite accurate, so I can't complain in the end for £8. I probably should have kept the original as a novelty!
 
My iPhone compass stopped working a while ago alas. Magnetic compass is fairly reliable, if kept away from magnet sources., and of course if you have taken it.

Always Polaris if you can see it.
 
Magnetic compasses in phones are also badly affected by magnetic contact chargers :-(
 
I was expecting you to say you'd relied on it to get down off the hill in the mist and fell down a cliff!

I'm sure a compass would be useful to know which direction to look for the ISS but if you need a compass to know where sunrise will be ........:thinking:
 
Aren't most older churches arranged on an East/West axis? (Within a few degrees, anyway!)
 
Nod said:
Aren't most older churches arranged on an East/West axis? (Within a few degrees, anyway!)
Click to expand...

Yes, I read up on this once and it was quite interesting in that the further west the church was located the more northerly of east it was aligned and they didn't know why. I doubt it was to do with iPhone compass calibration! Apparently the day of the year that the saint who the church was named for affected the alignment. Obviously due to the sun rising at different positions throughout the year.
 
I know it's easy to be wise after the event but It wouldn't have occurred to me to use the phone compass, rather I would have used (on my Android phone) Google Maps and/or Google Earth to see which way up north was and aligned myself accordingly vis-a-vis the church or the road next to it- assuming data was available where you were.
 
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