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New Magellan Explorist


dziner
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I purchased a yellow Garmin eTrex about a year ago from a friend for $30. I knew it was a good deal but wasn't sure what to use it for. Now I've found myself enjoying the sport of geocaching! Sometimes it loses signal under tree cover and I'm really not sure about the accuracy.

 

I see that Magellan is releasing three eXplorist models. The 100 is very basic but is WAAS enabled, the 200 has a built-in map region and is WAAS enabled, and the 300 has the built-in map region, WAAS enabled, and has a barometer and electronic compass. I'm considering the 200 or 300. Could anyone tell me why I may find the compass and barometer handy for geocaching? This weekend a cache I was loking for had an elevation in the description but my Garmin was about 40 feet off (elevation wise) which just couldn't be right considering I was at the top of the hill.

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What you will find handy for geocaching is a computer connection. The Explorist has none, so to me is nearly useless for geocaching. If you never use your computer to download waypoints to your GPS, then I could see these as being attractive little units, but for myself, I wouldn't even consider them for geocaching.

 

If I happen to be wrong about this, could someone please say so?

 

--Marky

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You are right about the download ability...

 

I work with dziner, and we were talking about this post today. One question we both had was how does the standard eTrex and most other GPS units know elevation when compared with a unit that has a barometric altimeter and is one more reliable then the other.

 

How does a GPS without Barometrice altimeter know the elevation? Is it accurate? How accurate are the units with Barometric altimeters in them? Do they have a setting to allow you to calibrate your unit to account for changes in higher or lower pressure weather systems?

 

- Ed

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How does a GPS without Barometrice altimeter know the elevation? Is it accurate? How accurate are the units with Barometric altimeters in them? Do they have a setting to allow you to calibrate your unit to account for changes in higher or lower pressure weather systems?

GPS receivers inherently calculate a position in 3D space. First they determine your position in space by using the synchronized timing signals sent from the satellites together with the satellite ephemeris that precisely defines its orbital position. Then a mathematical model of the earth's shape is used to determine how your position in space can be converted to your lat/long and elevation above the earth's surface. The accuracy of the elevation measurement is pretty good but not quite as good as the horizontal (lat/long) position measurements.

 

There are two reasons for the decreased accuracy - one is that you get better accuracy if the satellites are spread out. For determining your latitude it's best to have some sats north of you and some south, similarly for longitude it's best to have some to the east and some to the west. For altitude it'd be best to have sats both above and below you - but unfortunately you can't get signals from any below you since they're blocked by the earth. The second source of inaccuracy is that the mathematical model of the earth's shape used is rather coarse and doesn't always have the right value for the difference between the ellipsoidal shape of the WGS84 model and the geoid shape of the sealevel surface of the earth. As a result, without WAAS, horizontal accuracy is about 20' and altitude accuracy is about 30 -40'.

 

Most of the GPS error in both horizontal and altitude positions is random and fluctuates fairly rapidly. OTOH, pressure-based altimeters have smaller random errors (around 5 - 10'), but are subject to substantial drift of hundreds of feet due to changing atmospheric conditions. That's why such altimeters need to be recalibrated regularly when at places of known elevation.

 

The Garmin GPS units with pressure sensors (Vista, Summit, 76s/cs, 60cs, Geko301) can use both types of measurement together. By comparing the reading of the pressure sensor with the GPS reading over a period of about half an hour, the unit can correct for changes due to weather systems while also smoothing out any random fluctuations in the GPS reading. This avoids the need to manually recalibrate although the units do allow that as well.

 

Note that Magellan's current unit with a pressure sensor (the Mer. Plat.) does *not* use it for determining altitude. It remains to be seen what the details are on the eXplorist 300 and how the GPS and pressure sensor work together in that unit.

 

BTW, I agree with Marky that the lack of a computer interface is a fatal flaw of the eXplorist 100/200/300 - not only for geocaching but for many other applications of GPS units.

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MacGPS Pro and GPSy are two programs that support both Garmin and Magellan GPS receivers using Mac computers.  The eXplorist 100/200/300 lock you out of many useful applications of GPS receivers using either PCs or Macs.

gpsbabel works just fine on MacOSX. You have to be comfortable with the command line to get it to do what you want, but it will do just about anything.

 

Maybe someone will write a MacOSX frontend for it, like GSAK on Windows.

 

--Marky

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FYI: Mac SimpleGPS X has Magellan support in their drop down menu. The program is a GUI-based way to organize and upload/download waypoints in .gpx format. I use an etrex with it (yup, the yeller one like you until I figure out how much I'm willing to spend to upgrade), so I can't vouch for actual Magellan usability, but its there. And Mac SimpleGPS X is free.

 

The only issue I've had with using the software is the very long amount of time it takes to import a large (~200 waypoint) .gpx file. it's pretty zippy on upload and download, though. I only run PQs about 1x week and let it run and go do something else, usually.

 

www.macsimplegps.com

Edited by BuckyDef
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The only issue I've had with using the software is the very long amount of time it takes to import a large (~200 waypoint) .gpx file.

Maybe if you weren't still using a Mac SE running Mac OS 8 and got an iBook, it would be faster. <_<

 

--Marky

Yeah, my titanium G4 is already outdated ... :blink:

 

Of course, my windoze box at home is so old I'm afraid to put it on the network :o

 

I just downloaded the new beta release of Mac SimpleGPS -- looks like I was out-of-date anyway. If anyone is interested in whether a 200 waypoint PQ will import in less than 2 hours using the "new" release, I'll let them know.

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BuckyDef, maybe I'll download SimpleGPS and purchase the connection kit/serial-USB adapter for the Garmin eTrex. The only thing this doesn't give me is WAAS. I'm only using the GPS for geocaching. Oh, I have an Apple G5 running OS X Panther so what ever processing time it takes should FLY. I think the only thing that would effect putting/getting waypoints would be the serial-to-USB converter needed with the connection kit.

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BuckyDef, maybe I'll download SimpleGPS and purchase the connection kit/serial-USB adapter for the Garmin eTrex. The only thing this doesn't give me is WAAS. I'm only using the GPS for geocaching. Oh, I have an Apple G5 running OS X Panther so what ever processing time it takes should FLY. I think the only thing that would effect putting/getting waypoints would be the serial-to-USB converter needed with the connection kit.

I've not had a problem using a $10 cable fo etrex->PC serial and a keyspan USB adapter. You can run any number of Mac waypoint software programs to upload/download on either Garmin or Magellan, as discussed in prior posts. Mapping in either Garmin or Magellan is the only thing that is totally Mac-unfriendly, and the yeller doesn't do that anyway. This is currently my main issue with upgrading my geocaching setup, since it would entail loading maps to the GPSr from my Win98SE computer, and downloading PQs to the GPSr and Palm from my Mac (talk about extra steps...). I don't think either Garmin or Magellan have any plans to port their mapping software to Mac anytime soon though.

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gpsbabel works just fine on MacOSX.  You have to be comfortable with the command line to get it to do what you want, but it will do just about anything.

 

Maybe someone will write a MacOSX frontend for it, like GSAK on Windows.

 

--Marky

While it isn't a geocaching-specific front end, do note that an alternative interface was contributed to GPSBabel about a year ago. It's more capable than the windows gui for GPSBabel. See http://gpsbabel.sourceforge.net/osnotes.html

 

macgpsbabel02.jpg

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WAAS is over-rated. My SporTrak Pro has WAAS turned on all the time (It takes VOODOO to turn it off). Renegade Knight has WAAS turned off on his GPS V. There is no difference in performance when we cache together. This is because there are not enough WAAS enabled Satellites on our horizen to make a difference. I wouldn't choose a GPS using this as the deciding factor. Check the other features out to make your deicision. If this unit will not allow a computer connection it is not a good deal. Right now I am using a GPS 60CS with USB. I cannot believe the difference in download speeds. I would buy this unit for this feature alone. Now if I could only get it to work properly. :rolleyes:

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I have the eXplorist 100 and compared to my eTrex, it works much better under heavy tree cover. It's very simple to use, has an intuitive interface and is nice-looking. I don't care that it doesn't have a computer interface. I enter waypoints by hand and usually no more than a few at a time anyway. People who prefer downloading waypoints will not want this one, but I really like it. It consistently holds a good lock on the satellite signals and is more accurate in the vicinity of waypoints than my eTrex ever was. The eTrex's distance reading would bounce around from 15-55 ft. in the vicinity of a waypoint when I barely moved the thing. The eXplorist does not do this.

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