----------------------------Original message----------------------------
 
Courtney:
 
         I would trust your GPS before I'd trust a DMA/NIMA nautical chart. My
experience with NIMA is they are very careful how they deal with civilian
inquiries concerning position discrepancies; could be a trap from some hapless
mariner intent on litigation.  NIMA's official company line is that they welcome
such reports of discrepancies. Mariners (and others) can report such findings to
NIMA using the MARINE INFORMATION REPORT AND SUGGESTION SHEET tucked into the
rear of weekly NOTICE TO MARINERS; I can FAX you a blank copy if you wish.  But
my gut, unconfirmed feeling is they don't place much importance on following up
such reports from civilian mariners; I've tried myself and gotten nowhere.  U.S.
Navy position discrepancy reports carry much more weight and are likely to
result in immediate action such as a bulletin in Notice to Mariners and revised
editions of charts.  The U.S. Navy, of course, is NIMA's prime customer.
          I find it interesting that NIMA would blow you off by referring you to
National Ocean Service who in my experience rarely follows up with questions
from civilians.  You likely spoke to the wrong person at NIMA. I suggest sending
your message via e-mail thru the NIMA web page feedback site.  They are really
quite good at answering questions like this and you might luck out and find
someone to respond who likes nothing better than to chatter endlessly about
position discrepancies.
           Hope this chatter helps somehow.
 
- Paul Leverenz
  Library
  Scripps Institution of Oceanography
 
______________________________ Reply Separator _________________________________
Subject: DMA standards and accuracy
Author:  [log in to unmask] at @UCSD
Date:    3/17/98 2:01 PM
 
 
----------------------------Original message----------------------------
Hello,
 
I sent the below message to NIMA who pointed me toward NOAA and from
whom I haven't heard yet. The map librarian at the University of
Washington suggested I direct my questions toward this listserve.
 
I'm curious about DMA map accuracy in the central/western, tropical
Pacific.  A meteorological research project that my group is involved
with is underway in the Marshall Islands. We have 17 rain gauges
between 7-9.5 N and 166-169 E. A GPS receiver was recently sent out to
get exact lat/lons of the gauges, however, 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. What is the
DMA standard for island locations on their nautical maps? Are the
locations accurate to within a km? I understand that there could have
been errors in the GPS readings but I'm trying to bound the possible
error of the DMA maps. Any information or references would be
appreciated!
 
Thanks,
Courtney Schumacher
 
--
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Courtney Schumacher           INTERNET: [log in to unmask]
Dept of Atmospheric Sciences
Box 351640                    TEL: (206)685-1073
University of Washington
Seattle, WA  98195-1640
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>Subject:      DMA standards and accuracy
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