Earlier in the month, back at reference 2, I reported acquiring the Ordnance Survey (OS) mapping app for my telephone. Which has proved very satisfactory - with the exception of the compass provided.
The app - having failed to find out how to do screen capture on the telephone - looks something like the Powerpoint sketch above.
Now both the vertical telephone or the horizontal telephone can be considered to be pointing in some particular direction. In the case of horizontal, the direction is parallel to the long axis of the case.
There are, in effect, two compasses. The proper compass is the rectangle at the top of the screen, just below the backward facing camera lens. You get a moving pecked scale running along the bottom, marked with letters for the points of the compass: NW, N, NE, E and so on, with your direction being given in the middle. Above that, you get a number in the range 0° thru 360° giving you your direction in degrees, with north being 0° or 360°, probably depending on the direction of rotation.
Then if you are actually on the map, you also get a red chevron, something like that on the snap above, where it is on the bend of Jubilee Way before you get to the railway bridge, the anti-clockwise Jubilee Way run having been popular during the plague and for a while after that. The chevron points in the direction that you are facing, that is to say in the direction of the telephone, in this case west, roughly parallel to the east-west lines of the National Grid marked in blue.
As you swing around, the chevron in the middle of the screen and the compass at the top of the screen swing around with you, more or less in sync.
But sometimes, it is quite wrong. On one occasion the map was displayed with the Grid running diagonally across the screen. Then just now, the compass was getting on for 180° out, saying roughly south when the telephone was pointing roughly north. Stopping and restarting the app seemed to cure that particular problem.
And other times it is slightly wrong. I am in the study upstairs, one of the back bedrooms, and if we assume that the front of the house is parallel with the road, with the walls of the study corresponding, the compass might be 20 or 30 degrees adrift of what I know to be the direction of the road. Furthermore, the direction of the chevron in the middle only approximates to that given by the compass at the top. Although one needs to remember that the chevron rotates quite slowly, and may take a few seconds to settle down to what it thinks is the right direction.
I had assumed that the telephone compasses were not magnetic, rather that they were driven by signals from the telephone masts dotted about, but if that is the case, why are they not more reliable?
Checking with my Ottawa magnetic compass (as first noticed at reference 3) is no good, as there is far too much steel in the study. I think the radiator is the main culprit. Not sure about the telephone and the laptop.
Checking with Gemini, he explains that the compass inside the telephone is based on a very small magnetometer built into its chip, nothing to do with telephone masts - but prone to the same problems with nearby iron & steel as magnetic compasses. He also suggests that the software involved is pretty complicated and can be a bit creaky. He tells me that there is no aerial strip giving direction, rather that direction is a function of the position of the magnetometer itself inside the chip, presumably fixed with respect to the case of the telephone. He talks of needing to calibrate the compasses, although he is the first so to do.
I might say that his explanation seemed pretty good - although I shall not go to the bother of checking him.
Just presently, that is to say early Wednesday morning, leaving the Ottawa compass aside, the compasses on my telephone seem to be behaving themselves. We will see how long that lasts. I suppose I need to take both compass and telephone out into the middle of Court Recreation Ground, far away from any street lights or radiators, and see how I get on there. The land drains there are less than thirty years old and are probably plastic.
Maybe there will be further report later today.
PS 1: supplementary: I have just remembered about magnetic north. Gemini tells me that the telephone uses GPS and other location data, combined with declination data from some database, to make the correction. So the telephone masts probably do come into it after all. He reminds me that here in the UK, magnetic north is presently pretty close to true north. The same, for my purposes.
PS 2: Wednesday afternoon: Court Rec. didn't work. It was too cold and my hands were far too unsteady. But I did think that while the compass and the telephone roughly agreed, it was only roughly. Also that there was some interaction between the two. Also that to do the job properly a large, steady table, paper and pencil would be useful. I learned that, after the overnight rain and land drains notwithstanding, the football pitch at the eastern corner was saturated, not fit to play on, and that there was surface water draining out of the northern corner into the veterinarian car park.
PS 3: I have just noticed the descriptor 'Rota Disconnections Alpha Identifier: K' attached to our address on our electricity bill from EDF. Bing reveals this is all about rota disconnections in the event of some power emergency. Has it always been there, or is there some concern about the security of power supplies?
References
Reference 1: https://explore.osmaps.com/. Entry point for OS maps.
Reference 2: https://psmv5.blogspot.com/2024/11/black-park.html.
Reference 3: https://psmv2.blogspot.com/2014/10/the-quest-for-new-compass.html.
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