I teach navigation to sailors and that involves a lot of use of ordinary gps sets, plotting onto charts etc. THe basic ''buy at halfords'' gps set of any manufacture will not give you a position fixaccurate to a foot under the best conditions. As has already been sai, issues like atmospheric conditions, location of satellites , electromagnetic onterference all can degrade the accuracy significantly.
As an illustration, I am sat on my boat right now in falmouth harbour and the fix on my boat gps ( raymarine) has an hdop (ie accuracy) of 1which is very good. But comparing the location given with that of the modern gps in this tablet there is a discrepancy of 0.01 minutes of latitude which is about 9 meters.
I'll put it another way. I always tell students that under no circumstances should they try to navigate blind through a harbour entrance using gps alone.
I can recommend two experts. One is to try the institute of navigation. The othe is a guy called Tim Bartlett ( a biker as it happens) who wrote the navigation textbook used by the RYA.
Any Cartographers or map makers here?
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I should add that the gps evidence could be questioned in another way. Not only is there the issue of the accuracy of the position fix which on your halfords type set is never ever to one foot, but most combined gps and map systems then adjust that position to fit in with the map ie if the car / bike position is two meters to the side of the road, they shift the position to put the car/bike on the road. Whether it is the original fix or the adjusted one that you download, I do not know
We dont know what sort of gps data you are dealing with. It seems likely that its from someones TomTom or similar, but the situation would be different if it were special equipment like that the military use and which is probably available to plod.
PS If you do find an expert who proves us all wrong, I would love to know how /why
We dont know what sort of gps data you are dealing with. It seems likely that its from someones TomTom or similar, but the situation would be different if it were special equipment like that the military use and which is probably available to plod.
PS If you do find an expert who proves us all wrong, I would love to know how /why
From what TC posted it sounds as though it's the raw GPS NNMEA log.
Map matching may be used for displaying your position on a vehicle's navigation system but it is extremely unlikely that would be logged.
Map matching may be used for displaying your position on a vehicle's navigation system but it is extremely unlikely that would be logged.
“Scientists investigate that which already is. Engineers create that which has never been.”
-- Albert Einstein
-- Albert Einstein
It is the raw data GPS data (if that means anythingD-Rider wrote:From what TC posted it sounds as though it's the raw GPS NNMEA log.
Map matching may be used for displaying your position on a vehicle's navigation system but it is extremely unlikely that would be logged.
)But I hear what you guys are saying, and Lazarus, I may well come back to you in the not too distant future if you don't mind.
I will keep you posted.
It is better to arrive 30 seconds late in this world than 30 years early in the next
