NavList:

George Huxtable wrote:

> Only when an object is firmly fixed in deep water, such as a dolphin
> or a jetty, can one sail up to it, and record a GPS position.. A
> tethered floating buoy is usually too mobile to be used for such a
> task. So one has to rely on taking positions of landmarks from the
> chart.

It all depends on the swing circle of the aid vs one's distance from it.
  If I'm a mile away from a buoy and it swings in a circle of 100 feet
(diameter) that's a +/- 1/2 degree change in bearing.  Most small boat
compasses can't be read that accurately....
>
> Not all charts are to WGS84. One has to be very careful, in such a
> sensitive application, to apply any offsets on the chart, to bring it
> into line with WGS84, or to set a GPS receiver to use the coordinate
> system of the chart (OSGB, for many of my charts).

Are we running with out-of-date charts, George?  <g>   Surely the new
ones are  WGS-84



> But not both, of
> course!
>
> However, if the observer uses that same chart to define his own
> position, rather than GPS, any such errors are eliminated.

Point taken -- and one the careful GPS user will take into account.


Lu Abel


--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---