Imray Electronic charts- not Georeferenced

[speedfiend]

Hi All,
I have downloaded the Eastern Mediterranean electronic charts from Imray for a charter holiday around Greece
Some of them display an electronic message saying "not Georeferenced " .
What does this mean ?
Will the vessel(this iPad ) appear as a boat icon on the charts when I arrive in Greece next week?
Thanks
Stuart

 

[prv]

It's ten years or more since I was last in that part of the world, but at that time the paper charts were well known to have position errors due to the age of the surveys they were based on. So the relative positions of islands, ports, etc were correct, but the actual lat and long would be off by quite some distance. For the kind of "turn right at the next island" eyeball navigation we were doing this was of no consequence whatsoever, we never used to plot a GPS position on the chart anyway.

Maybe the Imray warning is saying that the same applies to their raster charts? So the little boat icon will appear on the chart, but it may be up a mountain or on the other side of the island depending on the position error on that bit of the chart?

Pete

 

[speedfiend]

Ok thanks Pete.
Only some of the charts pop up this notice , so maybe they are the older ones.
Will rely on visual navigation rather than electronic !

 

[prv]

Ok thanks Pete.

Don't take my word for it - I'm only guessing

I would suggest asking the developer, but sadly the guy who did Imray's iPhone and iPad apps for them died earlier this year: http://www.ybw.com/forums/showthread.php?427139-Imray-IPad-navigation . I don't know how much the app side of things was a one-man-band, but it's even possible that nobody now knows what that message means.

Pete

 

[southseaian]

The chart will use a different cadet point to the GPS which, unless adjusted otherwise, is WGS84.
In practical use this mean the position of the boat found by the GPS may be misplaced on the chart.
The chart will ((or should) show the correct details of the land and sea objects but the boat shown in the 'wrong' position because the GPS is giving a WGS84 and the details on the chart are related to a different datum
Important. Do not use the plotter to navigate near land or pilot the boat in a bay or harbour. This is OK'ish in the UK but will lead to danger in Greek waters.
Navigation is pretty easy line of sight stuff and most harbours simple to enter if the pilot book is followed. Few people will seriously bother with GPS although it's interesting and fun to play with the iPad.
Enjoy your holiday