Dennis Lee Bieber wrote:
> On Thu, 13 Dec 2007 15:26:20 -0500, singhals <singhals@[EMAIL PROTECTED]
>
> 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 re****ting
> 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
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