GPS Inaccuracy.

  • Thread starter Thread starter bob_tyler
  • Start date Start date
Considering the French don't even have a proper nautical chart for getting up to Pontrieux beyond the bridge at Lezardrieux, what on earth did Navionics use for their source data? Not at all surprised you were "sailing through granite cliffs".
 
Re: SHOM ... BSB / Kap files ...

Haven't used either but I thought SHOM used HMSO data for UK coastal charts...?! Have you tried Mapmedia SHOM based electronic charting? I've found them to have excellent accuracy, perhaps you get what you pay for.
 
Re: GPS Inaccuracy. First after WGS84 ...

With the recent killing of Al Fuquarwe in Iraq (or whatever his name is), could it be that the Pentagon has introduced a Dilution of Precision to the entire system to protect their potential targets?
 
Re: GPS Inaccuracy. First after WGS84 ...

Ok .... so its look at settings working through till a strange one is found ...

Now this is where I suggest joining the GPS Navigator Group I run and get the "world-wide" membership looking at the problem and possible answer .... see my signature below for url.

Near 2000 members incl. GPS companys and chart / plotter people ... as well loads of novice and experienced GPS users .... all helping to get most out the gear ...
 
Re: GPS Inaccuracy. First after WGS84 ...

The error is probably because the chart plotter is using older charts with up-to-date corrections based on older OSGB36 Admiralty charts and the GPS is on WGS84.

The 100 metre error sounds suspiciously close to the kind of shift would get with the wrong datum.

The error quoted for GPS is actually more like a probability of being less than 100m for 90% of the time. Actually it can be kilometres out for a short time and still meet that specification. I worked on the inner workings of a GPS reciever and we used to get occasional horrible errors.

Worse still was the car-GPS which used map matching and decided it was on a parallel road some hundreds of metres away and therefore the GPS was lying. It suddenly changed its mind a few minutes later.


I think I would use an echo sounder to find a river channel and a GPS to make sure it was the right river.
 
Wouldn't know about James's plotter but our ECS (and others I have seen) produce the heading vector from COG, not the compass.

That is an absolute definite because even if I do not have our electronic compass sentences read by the ECS it still produces the heading vector. Also is often at great variance to the compass heading if in strong cross currents.

John
 
I don't know what Navionics use but a friend uses the French equivalent to the Ordinance Survey Road Map on his Yoeman plotter and found all the rocks etc were plotted spot on!
 
Bob,

Can't answer your original question.

However, I have navionics gold on my chart plotter and it does not show Radar (or Helston range if you are of new school). Now that is a grave omission IMHO. Cos it's big and steel and it would hurt if I hit it.

Just for reference.
 
Re: SHOM ... BSB / Kap files ...

MM - maybe .... I know that they changed their format .... so hopefully it is better.

I since have stopped using many of the chart packs on PC I had ... having now installed the Lowrance.
 
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