On Mar 12, 8:46 pm, DaveC wrote:
I was recently off the coast of Mexico and using a Garmin
chartplotter for position.
.....

I've been doing some research since my primary post. The NGA site has
some great information (pamphlet at
http://www.nga.mil/MSISiteContent/St..._GPS_index.htm
) and the NGA Light list for outside the US. To be fair the Garmin
chartplotter didn't have the dedicated Mexico Blue chart (a special
chip I believe) but only the built in chart/map. The reference Garmin
gave in the database was a Russian chart that was last updated in 2006
(this is out of memory) BUT my question still remains does Garmin use
the WGS coordinates of landmarks per the NGA light list for those
waypoints shown on those charts? The accuracy of our GPS position was
only as good as the DGPS would allow but I'd like to think the
landmark waypoint was correctly defined. Of note was the fact our
chartplotter happily rattled off positions to the 1000th of a minute
although everyone concedes the accuracy of GPS is only to the nearest
10th in those waters and the NGA only gives postitions to the 10th.
The cape we were looking at was Cabo Corrientes which is just north
of Cabo Roca Negra, the NGA has it defined at

15080 G 3482 Cabo Corrientes. 20° 24.0´ N 105° 42.8´ W Fl.W. period 6s
fl. 1s, ec. 5s 305 93
18 White truncated pyramidal octagonal tower, house with red cupola;
20.
RACON O(- - -)
The radar even had the RACON signal on screen so there was no
confusion about the landmark being the radar target.