On Wed, 9 Oct 2019 at 12:57, Simon Ritchie <simonritchie...@gmail.com> wrote: > However, that still leaves the fundamental problem: I can (and will) > publish the kit of parts for making your own base station. You could use > something similar to build a rover or you could buy one off the shelf. > According to the ads this will give you an accuracy of 2 cm, but how will you > check that you really are getting that accuracy?
At its heart, that's quite a complex question of metrology, geodesy, and maths. But really I'm not sure you need to worry about it too much with GPS. GPS receivers don't really exhibit constant errors (as I mentioned before, the antenna may introduce some but I suspect they'll be in the order of centimetres at worst), and the variable errors they exhibit are well-characterised. Any GPS fix you get will have error values provided with it, and you should be able to broadly trust those numbers. I'm sure there are commercial services which will give you a calibration result against a known receiver, but they will likely be expensive. Centimetre-level precision is close to the state of the art in GNSS/GIS and so services will be priced accordingly. The real question, really, is why you're aiming for that level of precision. Relative accuracy (i.e. consistency of measured points within a reasonably sized area) is much easier to achieve than absolute accuracy (which is not even an especially well-defined concept in this case). If you're just making these measurements to put into OSM, you have to realise that it's pointless to aim for accuracy better than 1m or so in OSM, as it will degrade over time due to the use of the WGS84 coordinate system which doesn't take plate tectonics into account. (Of course precision for precision's sake is a completely valid endeavour in my opinion. But, as I mentioned before, that rabbit hole can go extremely deep and is probably off topic here. I hope I've given you a flavour of that though!) Cheers, -- Russ Garrett r...@garrett.co.uk _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-gb