Oldhand
Well-Known Member
If you mean C-Map then I'm not too surprised at your problem.
Robin
Well-Known Member
We run 2 Navman C-Map plotters. One thing to check is that you have the WAAS/EGNOS differential turned 'off'. WAAS is not this side of the pond and EGNOS (the European one)is still under test and can be widely wrong, average fixes are better without.
G
Guest
Guest
Re: GPS Inaccuracy. First after WGS84 ...
Make sure WAAS / EGNOS is turned off on your machine ....
If I put it on with my machine - I get silly results !!
As a point of info - I have a set of charts produced by SHOM that I use in pc plotting ........... they are a joke and consistently place position about 400m NW of real ... so don't believe that the elctronic charts are as accurate as they should be !!
Make sure WAAS / EGNOS is turned off on your machine ....
If I put it on with my machine - I get silly results !!
As a point of info - I have a set of charts produced by SHOM that I use in pc plotting ........... they are a joke and consistently place position about 400m NW of real ... so don't believe that the elctronic charts are as accurate as they should be !!
savageseadog
Well-Known Member
I've done a position at home with a Garmin GPS with a clear sky view. Using Streetmap I've obtained a WGS84 position for the house and I find that they are apart by about 100m. I don't know what's at fault I havn't looked into this any further. Streetmap is OS based so should be OK. Conclusion is I suppose not to take anything for granted.
duncan
Well-Known Member
Robin - for a GPS unit fine but a plotter will match the GPS to the datum you select for your charting.
agree WAAS/EGNOS is the most likely culprit if switched on.
I was out Sunday with the plotters yep all 3....) on and enough secondary information to tell me I wasn't getting any errors such as the ones Bob noticed. And I can't believe I would have been using a different set of satelites 100 miles down the coast.
agree WAAS/EGNOS is the most likely culprit if switched on.
I was out Sunday with the plotters yep all 3....) on and enough secondary information to tell me I wasn't getting any errors such as the ones Bob noticed. And I can't believe I would have been using a different set of satelites 100 miles down the coast.
Robin
Well-Known Member
Duncan
We also have 3 plotters (oh and plus a Yeoman)! We run the Yeoman from one of the plotters and because not all our charts on board are WGS84 we have to toggle the plotter to send out European Datum or OS36 to match the paper chart before we plot anything on it seriously - miles offshore it doesn't matter. Our Raymarine plotter which is kept as a spare can have different datums set on the screen/chart from the GPS so I have a post-it note in the log to remind me to change BOTH to the chart datum if it is running the Yeoman. The Navman can select from various datums but will reset both the chart AND the GPS to the same datum so no room for error, both screen and Yeoman will be correct if set to the chart's datum. I'm sitting at the chart table now and have just tried it!
Robin
We also have 3 plotters (oh and plus a Yeoman)! We run the Yeoman from one of the plotters and because not all our charts on board are WGS84 we have to toggle the plotter to send out European Datum or OS36 to match the paper chart before we plot anything on it seriously - miles offshore it doesn't matter. Our Raymarine plotter which is kept as a spare can have different datums set on the screen/chart from the GPS so I have a post-it note in the log to remind me to change BOTH to the chart datum if it is running the Yeoman. The Navman can select from various datums but will reset both the chart AND the GPS to the same datum so no room for error, both screen and Yeoman will be correct if set to the chart's datum. I'm sitting at the chart table now and have just tried it!
Robin
Oldhand
Well-Known Member
[ QUOTE ]
Streetmap is OS based so should be OK. Conclusion is I suppose not to take anything for granted.
[/ QUOTE ]
If Streetamp is OS based you should be using OSGB36 datum on your GPS for fixing your house, not WGS84.
Streetmap is OS based so should be OK. Conclusion is I suppose not to take anything for granted.
[/ QUOTE ]
If Streetamp is OS based you should be using OSGB36 datum on your GPS for fixing your house, not WGS84.
Oldhand
Well-Known Member
Re: GPS Inaccuracy. First after WGS84 ...
[ QUOTE ]
As a point of info - I have a set of charts produced by SHOM that I use in pc plotting ........... they are a joke and consistently place position about 400m NW of real ... so don't believe that the elctronic charts are as accurate as they should be !!
[/ QUOTE ]
In what area are you getting that huge error with SHOM (I presume you mean SHOM based electronic charts) charts? I have had no problem at all with SHOM based electronic charts (Mapmedia) in Normandy and Brittany.
[ QUOTE ]
As a point of info - I have a set of charts produced by SHOM that I use in pc plotting ........... they are a joke and consistently place position about 400m NW of real ... so don't believe that the elctronic charts are as accurate as they should be !!
[/ QUOTE ]
In what area are you getting that huge error with SHOM (I presume you mean SHOM based electronic charts) charts? I have had no problem at all with SHOM based electronic charts (Mapmedia) in Normandy and Brittany.
jamesjermain
Well-Known Member
I'm interested you had a positional problem over the weekend, 'cos I had a heading problem on my old b&w Raymarine plotter. Drifting back up the Tamar last night in the dark, the heading line was consistently way off to starboard of either the ships head or COG. Yet the charted position was spot on and the track was also correct. What was going on (there was not enough cross tide to justify this and it would have also given an offset to port from time to time)?
B
bob_tyler
Guest
Steve,
"I would start by checking the connections between the antenna and receiver,"
The antenna and plotter are all in one, no wiring.
Bob
"I would start by checking the connections between the antenna and receiver,"
The antenna and plotter are all in one, no wiring.
Bob
B
bob_tyler
Guest
Interesting, James.
I have my swinging mooring off the RCYC marked as a waypoint. When I got back there, possibly only about 3 miles, as a seagull flies, away from where I was getting inaccuracies, it was spot on.
Could it be that the electronic chart is considerably out in the River Fal? I don't know when it was last surveyed but it was probably well before the days of GPS. How about a Court Martial of the Chief Surveyor to the Royal Navy?
I have my swinging mooring off the RCYC marked as a waypoint. When I got back there, possibly only about 3 miles, as a seagull flies, away from where I was getting inaccuracies, it was spot on.
Could it be that the electronic chart is considerably out in the River Fal? I don't know when it was last surveyed but it was probably well before the days of GPS. How about a Court Martial of the Chief Surveyor to the Royal Navy?
gandy
Well-Known Member
Could the mud spit be changed from its charted location?
savageseadog
Well-Known Member
No, I'm converting the datums
B
bob_tyler
Guest
That is quite possible but does not account for my course being shown as over land covered in trees!
duncan
Well-Known Member
Robin,
Raymarine approach is surprising, and potentialy dangerous! Love the post it!
Yeoman is always a law unto itself ..............but great piece of kit.
Raymarine approach is surprising, and potentialy dangerous! Love the post it!
Yeoman is always a law unto itself ..............but great piece of kit.
Sailfree
Well-Known Member
Last year I found that according to Raymarine and Navionics charts we were sailing through Granite Cliffs to Pontrieux in N Brittany. I felt the chart of the river was wrong but have no evidence except that both had us right when in the estuary!
peterb
Well-Known Member
Surely the heading line is given by the compass, not GPS? If it doesn't seem to fit with eyeball observation, I'd check the fluxgate first.
jamesjermain
Well-Known Member
Good point
G
Guest
Guest
SHOM ... BSB / Kap files ...
Solent / Central Channel and also Baltic Latvian Coast.
Solent / Central Channel and also Baltic Latvian Coast.
B
bob_tyler
Guest
Re: GPS Inaccuracy. First after WGS84 ...
Nigel,
The WAAS/EGNOS is turned off.
Nigel,
The WAAS/EGNOS is turned off.
