GPS vs OS
Went out for a little run ridge run in the hills this afternoon, okay, okay, I know 2 hours to do 8 miles, I stopped for endless photo and product shots, which I may use in the future – plus the technology gave up on me about 1 mile from home as you will see!
Still, that isn’t the reason that I posted this. If I tell you that the highest point I got to was Penygadair, then take a look at the second image here…
The aficionados amongst you will know that the OS maps point to the highest point on Cadair Idris as 893m, yet my highly accurate GPS mapping says 954m!!! I’d be grateful if someone could explain this one to me…
Any road up, what a beautiful day it was:
Llyn Cau
From Penygadair to Pen Lleyn






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Ched Apr 10, 02:21 AM
If all (or most) of the satellites were directly above you when you took the reading – the GPS receiever may find it difficult to triangulate elevation. I’ve noticed when the satellites are low in the sky that there is an improvement in altitude readings.
Gwilym Williams Apr 12, 12:08 AM
This is a good warning! Whilst such gadgets are useful they cannot be 100% foolproof; and we should take care that we are not be lulled into a false sense of security by them, when running on the hills in fog for example.
Recently a friend of mine’s SatNav directed his camper van onto a supermarket carpark when he had set course for a bridge over a river! So it goes!
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