Dennis Lee Bieber wrote: > On Thu, 13 Dec 2007 15:26:20 -0500, singhals <singhals@erols.com> > declaimed the following in soc.genealogy.computing: > > >>Which models in which brands will allow me to retrieve >>lat/lon a week after I mark the spot? Not all of 'em do, >>apparently. >> > > Every GPS unit I've owned (and I'm up to my fourth generation unit > now) retained all way points until manually deleted by the user. Yeah, it'll show me the street address and the map location, but NOT the lat/lon. > > The /number/ of retained way points varied -- I think my first unit > could hold 50 way points and one route of 20 or 30 of those points. My > current unit has some 500-1000 way points, and between 20-50 routes of > 30 or 50 way points each. > > A GPS unit without way points is basically useless -- it can show > you where you are NOW, but can not guide you to a location. > > Took me forever to clear out stray way points on my last trip to the > former ConiFur NorthWest (furry convention)... I had the GPS plugged > into a Kenwood D7 radio running in APRS (automatic position reporting > system); Every 2 minutes my call-sign and position, as retrieved from > the GPS, were transmitted, and as I recall the call-sign and position of > any received signals were recorded as way points on the GPS [It's been > five years so memory could be wrong -- maybe it was just the radio > message log that took forever to clear out]. > > For a new GPS unit, in CONUS, things to look for: 12-channel > parallel receiver (really old units -- my first -- were 8-channel > sequential). WAAS enabled. Desirable features: averaging (you leave the > unit on in averaging mode for some time without moving it and it refines > the location over time, rather than having instantaneous position that > changes with each update as the NAVSTAR birds move in orbit) > > I'd also suggest using UTM rather than Lat/Long... Since UTM is a > metric readout, you can easily compute things like: 10 meters true north > of "xyz mausoleum gate", 5 meters east... a description easier to > visualize than a pair of lat/long values that differ in some decimal > place -- especially as an arc minute of longitude at the equator is > about a nautical mile, but maybe only half a nautical mile at latitude > 60 (and only a few inches near the pole) Except, I _understand_ lat/lon (g). > > And you /should/ reference to some distinctive, and unlike to move, > landmark, as just recording a lat/long (or UTM) directly from the GPS > unit can still be off up to 10meters (though with WAAS and clear sky, > more likely the extreme drift is 3-5meter). Even a 5m error for your > recorded position, combined with a 5m error for someone coming back next > year, could result is their position being 30 feet away from where you > were standing... > > GPS1...............Actual > your 5m error Actual...............GPS2 > a year later > > 30 feet could be a LOT of graves! Understood. In my primary interest case, if you can get within 30 ft you ought to see the fence ... and it ought to still be there, it was built to LAST. > > Using UTM with a reference landmark means that the GPS2 person can > compare their reading to your record and determine "I'm reading 10 > meters to the east of the recorded values... so if I add 10 to the > recorded UTM eastings, I get numbers that my unit should display today" > (I emphasize the "today" as even a few hours could result in drift) There's a stream nearby but nothing else guaranteed not to change in the next decade. S'why I'm so anxious to get a lat/lon on the place. They're talking about re-routing a major road and if they do I might not find the place again without lat/lon. Cheryl

singhals <singhals@erols.com> wrote in news:jNednT_yeK_HMv_anZ2dnUVZ_tGonZ2d@rcn.net: > Dennis Lee Bieber wrote: > >> On Thu, 13 Dec 2007 15:26:20 -0500, singhals <singhals@erols.com> >> declaimed the following in soc.genealogy.computing: >> >> >>>Which models in which brands will allow me to retrieve >>>lat/lon a week after I mark the spot? Not all of 'em do, >>>apparently. >>> >> >> Every GPS unit I've owned (and I'm up to my fourth generation >> unit >> now) retained all way points until manually deleted by the user. > > Yeah, it'll show me the street address and the map location, > but NOT the lat/lon. > Maybe the GPS's you've seen/used were dedicated to streets & driving directions? Only a guess, because my Magellan Explorist 210 is for hiking & geocaching and everything it does is based on the lat/lon or other selected format of N-S-E-W position. The waypoints & points of interest stay in the unit until you erase them or write over them in the case of breadcrumbs, but even the breadcrumbs can be saved to the internal memory storage. And for what it's worth, Google maps, Google earth & others give you (and you can search by) lat/lon coords. Try this: 1. Go to http://maps.google.com/maps and 2. type this into the search box: 39.170098,-76.67362 then 3. click on the Satellite button on the map and zoom in as far as you can. (It's the cenetery at the end of Runway 4 at BWI airport). The coords came from me visually finding the airport in Google maps, zooming in to the max and centering the map, then clicking the "Link this page" and copying the link info with coords. >> >> The /number/ of retained way points varied -- I think my first >> unit >> could hold 50 way points and one route of 20 or 30 of those points. >> My current unit has some 500-1000 way points, and between 20-50 >> routes of 30 or 50 way points each. >> >> A GPS unit without way points is basically useless -- it can >> show >> you where you are NOW, but can not guide you to a location. >> >> Took me forever to clear out stray way points on my last trip to >> the >> former ConiFur NorthWest (furry convention)... I had the GPS plugged >> into a Kenwood D7 radio running in APRS (automatic position reporting >> system); Every 2 minutes my call-sign and position, as retrieved from >> the GPS, were transmitted, and as I recall the call-sign and position >> of any received signals were recorded as way points on the GPS [It's >> been five years so memory could be wrong -- maybe it was just the >> radio message log that took forever to clear out]. >> >> For a new GPS unit, in CONUS, things to look for: 12-channel >> parallel receiver (really old units -- my first -- were 8-channel >> sequential). WAAS enabled. Desirable features: averaging (you leave >> the unit on in averaging mode for some time without moving it and it >> refines the location over time, rather than having instantaneous >> position that changes with each update as the NAVSTAR birds move in >> orbit) >> >> I'd also suggest using UTM rather than Lat/Long... Since UTM is >> a >> metric readout, you can easily compute things like: 10 meters true >> north of "xyz mausoleum gate", 5 meters east... a description easier >> to visualize than a pair of lat/long values that differ in some >> decimal place -- especially as an arc minute of longitude at the >> equator is about a nautical mile, but maybe only half a nautical mile >> at latitude 60 (and only a few inches near the pole) > > Except, I _understand_ lat/lon (g). > >> >> And you /should/ reference to some distinctive, and unlike to >> move, >> landmark, as just recording a lat/long (or UTM) directly from the GPS >> unit can still be off up to 10meters (though with WAAS and clear sky, >> more likely the extreme drift is 3-5meter). Even a 5m error for your >> recorded position, combined with a 5m error for someone coming back >> next year, could result is their position being 30 feet away from >> where you were standing... >> >> GPS1...............Actual >> your 5m error Actual...............GPS2 >> a year later >> >> 30 feet could be a LOT of graves! > > Understood. In my primary interest case, if you can get > within 30 ft you ought to see the fence ... and it ought to > still be there, it was built to LAST. > >> >> Using UTM with a reference landmark means that the GPS2 person >> can >> compare their reading to your record and determine "I'm reading 10 >> meters to the east of the recorded values... so if I add 10 to the >> recorded UTM eastings, I get numbers that my unit should display >> today" (I emphasize the "today" as even a few hours could result in >> drift) > > There's a stream nearby but nothing else guaranteed not to > change in the next decade. S'why I'm so anxious to get a > lat/lon on the place. They're talking about re-routing a > major road and if they do I might not find the place again > without lat/lon. > > Cheryl

singhals wrote: > > Understood. In my primary interest case, if you can get within 30 ft > you ought to see the fence ... and it ought to still be there, it was > built to LAST. Doesn't the US have anything equivalent to the UK's OS grid references? If you have a grid ref. - which you would work out by comparing what's on the ground with a current map - then even if there is considerable redevelopment, new roads, diversions of streams, etc. once the area ha been remapped you could look up the reference on the new map and thus refind the location on the ground. And don't be too sure about lasting! If you enter 414300,408300 into www.streetmap.co.uk as grid coordinates it will point to what was a burial ground. This isn't the cemetery currently marked on the map because the local council turned it into a mini-park and removed as many of the grave markers as they could get away with. Those left aren't in the original locations, some of them are being used as paving stones! -- Ian Hotmail is for spammers. Real mail address is igoddard at nildram co uk