----------------------------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 -- --------------------------------------------------------------------- Courtney Schumacher INTERNET: [log in to unmask] Dept of Atmospheric Sciences Box 351640 TEL: (206)685-1073 University of Washington Seattle, WA 98195-1640 --------------------------------------------------------------------- >-- Saved internet headers (useful for debugging) >Received: from postal.sdsc.edu (postal.sdsc.edu [132.249.40.114]) by mail.ucsd. >Received: from listmail.cc.uga.edu (listmail.cc.uga.edu [128.192.232.10]) by po >Message-Id: <[log in to unmask]> >Received: from uga.cc.uga.edu by listmail.cc.uga.edu (LSMTP for Windows NT v1.1 >Received: from UGA.CC.UGA.EDU (NJE origin LISTSERV@UGA) by UGA.CC.UGA.EDU (LMai >Date: Tue, 17 Mar 1998 14:01:53 EST >Reply-To: Maps and Air Photo Systems Forum <[log in to unmask]> >Sender: Maps and Air Photo Systems Forum <[log in to unmask]> >From: Courtney Schumacher <[log in to unmask]> >Subject: DMA standards and accuracy >To: [log in to unmask]