Help with GPS

[Zimmer]

C.Bill, I hope you don't mind my crashing your thread with a few questions of my own. Having finally (ummm, sort of ) mastered the digital camera thing, I've been trying to figure out the GPS thing.

At the eTrex Vista link posted earlier in this thread, there is a link in a box on the right to "Launch showcase", from which one can click a second link to see a comparison of the different Garmin units. Sorry, it's a Flash program so I can't get a link.

Three questions: 1) Only two of them -- the "Legend C" and the "Vista C" claim that they are USB compatible. Does this mean that those are the only two for which waypoints don't have to be manually entered? I already have the NG Topo software. Is Topo relatively useless except with either of the above models?

2) Only two of them (Summit, Vista, Vista C) have a barometric altimeter. DougPaul earlier said that the barometric altimeter is more accurate than the GPS altitude; I wasn't aware that the GPS would tell you altitude at all unless you get a model with the barometric altimeter. Sounds like I'm wrong?

3) What is "Built-in Basemap"?

C.Bill, again, apologies for jumping in here with questions that may or may not be relevant to your own search.

 

[DougPaul]

Doug, do you think there is a way to 'jury-rig' an external antenna to an Etrex Vista?

Yes. It is called a reradiating antenna--consists of an active antenna (= a receiving antenna + an amplifier), a power supply, and a small transmitting antenna that is placed against the eTrex antenna. Not quite as good as a direct connection, but it works well enough.

I have an earlier version of one of these, I'm happy with it: http://www.pc-mobile.net/gpsant.htm, Model GART3X (MCX connector) or GART3B (BNC connector). The active antenna part can be used with a GPS with an external antenna connector if the connectors match (or you use an adaptor).

There are other manufacturers: try a search on "GPS reradiating antenna", check the archives of news://sci.geo.satellite-nav, or check http://www.gpsinformation.net.

Doug

 

[DougPaul]

At the eTrex Vista link posted earlier in this thread, there is a link in a box on the right to "Launch showcase", from which one can click a second link to see a comparison of the different Garmin units. Sorry, it's a Flash program so I can't get a link.

Works for me--mozilla on Linux.

Three questions: 1) Only two of them -- the "Legend C" and the "Vista C" claim that they are USB compatible. Does this mean that those are the only two for which waypoints don't have to be manually entered? I already have the NG Topo software. Is Topo relatively useless except with either of the above models?

Most GPSes have an RS-232 (com) connection. The Legend C and Vista C have only a USB connection. The model 60 and 70 lines have both.

The Garmin software talks to either RS-232 or USB. Many other packages talk only RS-232. NG TOPO! talks RS-232--I think they have USB in the works, but I don't know if it is here yet. Check the NG website. RS-232 is compatible with more software and devices, USB is faster. The NMEA GPS communications standard (for talking to or getting data from a GPS) applies to RS-232 only.

2) Only two of them (Summit, Vista, Vista C) have a barometric altimeter. DougPaul earlier said that the barometric altimeter is more accurate than the GPS altitude; I wasn't aware that the GPS would tell you altitude at all unless you get a model with the barometric altimeter. Sounds like I'm wrong?

GPS will give both a location and altitude. The average GPS altitude error is on the order of twice the position error. A GPS-auto-calibrated barometric altimeter is more accurate than either alone. (The GPSes without a barometric sensor will just output the GPS altitude.) The 60CS and 72CS also have barometric sensors.

3) What is "Built-in Basemap"?

A basemap is a coarse roadmap built into the GPS. It will be covered up by any maps loaded into the GPS.

BTW, if you get a mapping unit, I suggest that you get one with a minimum of 24MB of mapping memory.

Doug

 

[WildPeaks]

Gps

If your looking for a nice unit for Bushwhacking, I can strongly advise the Garmin Geko 301.
Garmin, because they are very user friendly. I've been using them for boating since 1994 and I've had great success with them.
Geko, because they are light, small, so you can rig them to sit on top of your shoulder strap so the patch antenna can get a view of the sky, run on AAA batteries that match my other gear, and that's all I need to get the job done.
301, because it has the electronic compass, (the altimeter is nice if you don't already have one), The compass is necessary to orient the map page while your navigating to a waypoint when you are standing still. The compass can be shut off to save power when not needed.
I have National Geographic's TOPO 4.0 and I'll place waypoints of Summits & other important places on the mapping software and download them onto the GPS.
I leave it off most of the time until I start approaching a Bushwhack or other area that I need the unit for or sometimes I'll leave it on for a whole trip to mark the path we traveled that day. Just keep an eye on it after about 8-9 hrs., depending on your settings, and just change the batteries when they're low or out.
I never thought I would want a GPS for hiking, but when I started doing Bushwhacks, It's changed my mind and earned it's keep.
Speaking of worth, everything, including software, was somewhere between $300-$350 at EMS.
The mapping units may be fun, but IMO, not needed. I would rather save those bigger mapping units for entering a harbor.

 

[The Sikes]

Gps

I have a Garmin Vista Etrex and I thought it had nice features but I loose signal very easily and have been disappointed in that. Wish you could have an external antenae on it.

 

[DougPaul]

I have a Garmin Vista Etrex and I thought it had nice features but I loose signal very easily and have been disappointed in that. Wish you could have an external antenae on it.

I also have an eTrex Vista and have pretty much always been able to get a lock when I needed it. There is always unit-to-unit variation, but there is also a reasonable chance that you could be doing something better. Hold the unit above your head, (GPS) face up. Fingers/hand away from the antenna (under the Garmin symbol above the display.) Move to a location with as much sky visible as possible. Other tips in post #18, this thread.

The primary advantage of an external antenna is that it can be placed in a better location than the GPS while still keeping the GPS accessible to the user. The external antenna will probably work about as well as the GPS if they are in the same location.

That said, there are locations where no GPS will work. (In some buildings, in a cave, underwater, etc.)

Doug

 

[Zimmer]

Works for me--mozilla on Linux.

Sorry, Doug, to clarify, I was also able to navigate to the comparison page, but I wasn't able to post a direct link to the comparison page -- only directions of how to get there -- because of the Flash thing. I'm sure there's a way to figure out the url, but it wasn't appearing in the browser window. Thus the clunky instructions of how to get there from the earlier link.

Thanks for your clear info about the RS-232 thing. That makes much more sense. I've got a spare serial cable hanging around and a slightly older version of NGTopo, so that should work fine for me.

GPS will give both a location and altitude. The average GPS altitude error is on the order of twice the position error. A GPS-auto-calibrated barometric altimeter is more accurate than either alone. (The GPSes without a barometric sensor will just output the GPS altitude.)

So how much of an error would this be? 20' or 200'? I will be hiking nearly exclusively in the Whites, and I'm not hardcore. For the first couple of years, I will likely use it for geocaching with the kids , as I think that might be the best way to get them out hiking happily with me a bit more often, and will be a decent way for me (and them) to learn a bit about the GPS. We might do some bushwhacking down the line, though, where it would be helpful to know how closely we're following a contour line. I also do some trailrunning, so sometimes I like to have an idea of how much elevation gain is behind me and how much is still to come. Obviously I can get a general idea from the map, too, so that's not a huge issue.

A basemap is a coarse roadmap built into the GPS. It will be covered up by any maps loaded into the GPS.

So if you're pretty much planning on downloading maps beforehand anyway, a basemap wouldn't be needed?

Finally, THANK YOU for your responses. Though I've read through the archives here and elsewhere, there were a lot of things that weren't clear.

 

[DougPaul]

Sorry, Doug, to clarify, I was also able to navigate to the comparison page, but I wasn't able to post a direct link to the comparison page -- only directions of how to get there -- because of the Flash thing. I'm sure there's a way to figure out the url, but it wasn't appearing in the browser window. Thus the clunky instructions of how to get there from the earlier link.

OK--no problem. I thought it was javascript and it is possible that it is not possible to post a url to a comparison.

So how much of an error would this be? 20' or 200'? I will be hiking nearly exclusively in the Whites, and I'm not hardcore. For the first couple of years, I will likely use it for geocaching with the kids , as I think that might be the best way to get them out hiking happily with me a bit more often, and will be a decent way for me (and them) to learn a bit about the GPS. We might do some bushwhacking down the line, though, where it would be helpful to know how closely we're following a contour line. I also do some trailrunning, so sometimes I like to have an idea of how much elevation gain is behind me and how much is still to come. Obviously I can get a general idea from the map, too, so that's not a huge issue.

Under ideal conditions (unobstructed sky), typical error bound is 95% probability of being within about 30 feet in location and about twice that in altitude. In realistic mountain hiking conditions (foliage + blocking terrain), the errors can be much larger.

I suggest that you take the GPS along on walks and trail hikes to practice navigating with it and to develop realistic expectations of what it can and cannot do. Then when you really need it, you should be ready to go.

I generally navigate by putting in waypoints for the trailhead, trail junctions, and summits and connecting them with a route. The GPS will happily tell you your altitude and how far to the next waypoint and, if you leave it on, will record a track of where you have been. When you get home, you can load the track into the computer and look at it on the big screen against a topo. (And if you want a higher quality track, you might consider the external antenna on a pole or on top of your head...)

So if you're pretty much planning on downloading maps beforehand anyway, a basemap wouldn't be needed?

The basemap is built-in--you cannot alter it, so it will be there. A map loaded into the GPS will simply obscure the portion of the basemap that it covers.

Finally, THANK YOU for your responses. Though I've read through the archives here and elsewhere, there were a lot of things that weren't clear.

Sure--happy to help. They are amazing, but complicated little beasts. I suspect that many (most?) buyers of consumer GPSes don't understand what they are buying. I followed news://sci.geo.satellite-nav (the premier newsgroup on GPSes--some real experts there) for a year, read http://www.gpsinformation.net etc, and read some of the manuals before buying my first unit. Initially got an eTrex Legend and then swapped it for a Vista to get the larger mapping memory. And I still follow the newsgroup.

Doug

 

[Neil]

Can anybody inform me as to the prinipal differences between Garmin's e trex and Geko series? I can see that there is a weight difference and there seems to be a price difference as well. Is there a performance difference?

 

[DougPaul]

Can anybody inform me as to the prinipal differences between Garmin's e trex and Geko series? I can see that there is a weight difference and there seems to be a price difference as well. Is there a performance difference?

Try Garmin's comparisons:
http://www.garmin.com/outdoor/compare.jsp

Doug

 

[masshysteria]

Who's the MAN when it comes to GPS? Doug the MAN!

 

[WildPeaks]

Neil,

I wouldn't say there is a performance difference, but some of the eTrex units have mapping and some other capabilities. Also has a slightly larger screen. If your looking for mapping features, I would bypass the eTrex series & head straight for the 60CS. It's a better unit. It has a different/better antenna with a larger screen. I would check out DougPaul's Garmin comparison chart & you'll see the differrence.

 

[DougPaul]

I wouldn't say there is a performance difference, but some of the eTrex units have mapping and some other capabilities. Also has a slightly larger screen. If your looking for mapping features, I would bypass the eTrex series & head straight for the 60CS. It's a better unit. It has a different/better antenna with a larger screen.

By and large, the fundamental GPS is similar in all of the units. The difference is in the details and bells and whistles.

If you are considering the 60CS, you might also consider the 76CS. Same as the 60CS + bigger memory + better basemap + tide tables + bigger price tag. Also a slightly different case layout. (I opted for a 60CS.)

You can save a few $ on either by getting the C version (-barometric altitude sensor - magnetic compass).

Doug