GL: Swinging

[KevinR]

> -----Original Message-----
> The charts are not necessarily accurate.  For example, on the Erie and
> Champlain Canals, I frequently look at my chart plotter only to
> discover my boat is happily cruising on land right next to the canal.  

Hi Fred,

As a general rule, positions on NOAA charts are extremely accurate! It is
the GPS chart plotter software coupled with errors inherent in the GPS
system that end up with chart plotters sometimes showing boats up on land.

When you only have a small number of satellites visible, and they are all in
one quadrant (or all overhead), the HDOP numbers are bad, and the GPS
accuracy is degraded. Of course back when Selective Availability was turned
on, GPS errors were far worse than they are today.

Kevin