Good question. Last weekend I carefully marked a waypoint at my takeout before putting in upriver, using about a minute of waypoint averaging. When I returned by river to the same spot, my Garmin 12XL told me I was .12 miles west of the waypoint! This was all done without maps, so the culprit must be selective availability. Robert's suggestion is a good one. My house is within a TOPO! map area, so I think I'll step outside, get a fix, upload it to TOPO!, and see where I am. :-) If a nautical chart program were more accurate, it would probably have nothing to do with the map, but with the software. GPS works the same wherever it is. Nonetheless, as Korzybski once said, the map is not the territory, and some maps are more accurate than others. Chuck Holst -----Original Message----- From: Tomckayak [mailto:Tomckayak_at_aol.com] Sent: Thursday, May 27, 1999 8:24 PM To: Chuck Holst; paddlewise Cc: njohnson Subject: Re: [Paddlewise] Download to Garmin 12X In a message dated 5/25/99 10:27:45 AM EST, CHUCK_at_multitech.com writes: > an also merge files, and, of course, you can also > download waypoints, routes, and tracks from your GPS unit to > Topo!GPS and save them. A track I downloaded from GPS 12 to TOPO GPS showed me paddling though a head land with a 50 foot cliff. I tried a different Datum and it made it worse. The whole track seemed to be off one way or the other. Is it the Garmin or the TOPO maps or the Government induced error factor. Would a Nautical Chart program be more accurate for on the water tracks? *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
When they were searching for the A6 that flew into the Rockies, SA was turned off. I marked my position on the beach, then a few hours later I decided to paddle in "on instruments" and followed the GPS to the beach. I landed on my footprints. That was with a 12XL. .12 miles is 633 feet. Way too much of an error and I'd be calling Garmin if I were you. Cya -----Original Message----- From: owner-paddlewise_at_lists.intelenet.net [mailto:owner-paddlewise_at_lists.intelenet.net] On Behalf Of Chuck Holst Sent: Friday, May 28, 1999 10:07 AM To: 'Paddlewise' Subject: [Paddlewise] FW: Download to Garmin 12X Good question. Last weekend I carefully marked a waypoint at my takeout before putting in upriver, using about a minute of waypoint averaging. When I returned by river to the same spot, my Garmin 12XL told me I was .12 miles west of the waypoint! This was all done without maps, so the culprit must be selective availability. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
> When they were searching for the A6 that flew into the Rockies, SA was > turned off. I marked my position on the beach, then a few hours later I > decided to paddle in "on instruments" and followed the GPS to the beach. I > landed on my footprints. That was with a 12XL. .12 miles is 633 feet. Way > too much of an error and I'd be calling Garmin if I were you. I posted a trip report a while back that mentioned we never found the small Island in the middle of the river we were looking for. Someone pointed out to me that the advent of cheap GPS receivers were uncovering a lot of errors in maps. It would seem with the images I've seen on the internet of topo pictures from satellites that very accurate topo maps would be fairly simple. Woody *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
The problem with making accurate maps is that the world is not flat, and actually not a sphere either. The agreed conventions on how this distortion is dealt with and/or the differences in survey methods introduces known errors corrected with map datums (A simplification). A missing island may have in fact been missing! The island may have been surveyed in the 20s and been washed away or otherwise moved. cya -----Original Message----- From: owner-paddlewise_at_lists.intelenet.net [mailto:owner-paddlewise_at_lists.intelenet.net] On Behalf Of Robert Woodard Sent: Friday, May 28, 1999 4:34 PM To: Bob Denton; Chuck Holst; 'Paddlewise' Subject: RE: [Paddlewise] FW: Download to Garmin 12X > When they were searching for the A6 that flew into the Rockies, SA was > turned off. I marked my position on the beach, then a few hours later I > decided to paddle in "on instruments" and followed the GPS to the beach. I > landed on my footprints. That was with a 12XL. .12 miles is 633 feet. Way > too much of an error and I'd be calling Garmin if I were you. I posted a trip report a while back that mentioned we never found the small Island in the middle of the river we were looking for. Someone pointed out to me that the advent of cheap GPS receivers were uncovering a lot of errors in maps. It would seem with the images I've seen on the internet of topo pictures from satellites that very accurate topo maps would be fairly simple. Woody *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ *************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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