----------------------------Original message----------------------------
On Tuesday, March 17, 1998 2:02 PM, Courtney Schumacher
[SMTP:<a href="/scripts/wa-UGA.exe?LOGON=A3%3D9803%26L%3DMAPS-L%26E%3D7bit7BIT%26P%3D208615%26B%3D--%26T%3Dtext%252FplainTEXT%252FPLAIN%3B%2520charset%3DUS-ASCII%26pending%3D" target="_parent" >[log in to unmask]</a>] wrote:
> the GPS unit at times
> disagreed with DMA nautical maps of the area (map numbers: 81030,
> 81715, 81723, 81557, 81737). The largest disagreement was almost 20 km
> but in general the discrepancies were on the order of a km.
 
A couple of questions.
What datum are the charts on?  Did you convert the GPS readings to that
datum?
 
What are the sources and dates of the charts?  Some of the charts in the
Pacific are based on quite questionable surveys.  During my quartermaster
days in the late 70's many of the Pacific charts still cited surveys done by
Captain Cook.
 
What kind of GPS receiver?  How long on each target?  Skill level of
operators?
 
Bill Belton
<a href="/scripts/wa-UGA.exe?LOGON=A3%3D9803%26L%3DMAPS-L%26E%3D7bit7BIT%26P%3D208615%26B%3D--%26T%3Dtext%252FplainTEXT%252FPLAIN%3B%2520charset%3DUS-ASCII%26pending%3D" target="_parent" >[log in to unmask]</a>