Can someone tell me the deference between a system that comes as an option in a car with a monthly fee and one that you can buy as an add on and use in your car or in your home with no fee? Also are both types the same?

Like he said, plus there's also a sweet little add-on that will give you sub-meter accuracy. The buzz-phrase is, "real-time differential GPS", conveniently abbreviated to dGPS. It costs about $4K - $10K or so for the receivers. If you live near Loran stations, you're in. If not, you get to pay a subscription to somebody like Racal to access their differential signal.

But then, who needs submeter GPS?

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I was under the impression that the systems you buy in Best Buys are programed onto a hard drive and must be up dated every year. The system my friend has in his Lexus does not and he is charged 12.00 per mo. for the use of it.

I mean, I know where everything is in town:p . "Ok, tell me a new way to get to work".... no, no "show me the long way to mom's house"...

Seriously, can you ask it to look for like restaurants etc in a town you are not familiar with? or its just a map but u need directions? Ok, so I have been out of it for a while< lol

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1995 E320 smoke silver / parchment

There is a BIG difference between GPS and "On-Star" type systems. One has an active communication system with an operator. GPS simply shows your location.

GPS needs no subscription or anything else. As to accuracy, no one that is not surveying needs <1M accuracy. Buy a 12 channel unit that overcomputes the solution (like a Magellan) and uses WAAS, and you have 1-3M accuracy.

Got a spare few hours?

http://www.gpsinformation.net/

BTW, I use a Magellan Sportrack for hiking,and it's great. Highly recommend Magellan units.

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John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

Thanks for the info, when you say "<1M" you mean M as in mile or meter?

I used to like the TeleAid on my prior E320. Middle of the night, you want to grab a bite or you are in a hurry to go to dinner, call em up , they would arrange my reservations or tell me what was open at 4am when I got out of a club, for example. So it was live people to talk to. THAT"s what I would like, but would settle for being able to have a menu to choose from on the GPS, ie "show me BK within 1 mile" ....

Anything like that on the market?

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1995 E320 smoke silver / parchment

You Yanks! There is no such thing as a "mile." It's meters.

LOL, OMG close as in "meters" or within meters, that is f'n close as ****!!

So is there one that you can pay for the extra service if it didn't come on the car? U know u call them up on the cell, they locate u on their system, shoot directions to your gps... voila...

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1995 E320 smoke silver / parchment

One meter (usually about .3m) with real-time, dGPS.

The add-ons like locations and phone numbers for restaurants, bars, and hospitals are subscription-based. Lesser info can be had for free. Look for Tiger files, digital orthophoto quadrangles, topographic maps, and shape files on the internet. Your better GPS systems can display them as backdrops with your position superimposed.

any good RT system to use in the car w/ laptop?

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72 W114/M130

RedMeat cartoon

There is a wealth of PD software.
Delorme supplies a large inventory of didigtal maps for the world. Also try USGS (ahem) and CIA. They have free or low-cost digital maps.

ESRI has some useful software for connecting and using GPS & laptops and also PDA's. ESRI has a large, confusing website. ESRI makes the defacto standard vector Geographic Information System (GIS).

For GPS I use mostly Trimble products and have found them to be very reliable under some pretty bad conditions. Their GPS are more rugged than they indicate. They have a large, confusing website, too.

I saw a demo of a product for airplanes whose name escapes me. I've used it an its pretty good. It uses standard, digitized aeronautical charts on which it displays a continuous track which can be stored to the computer. We use it to fly repeated observational surveys over the same route. Its a heck of a lot easier than std nav aids.

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Never heard of it Narwhal. But that doesn't mean much. I rarely go offshore anymore and when I do, its as passenger. Last time I navigated with, "...a tall ship and a star to steer her by." Well, not really. The last time I had to get an accurate position I just fired-up the GPS and got within 0.5 meters in about a minute.

I've done it with a theodolite, 30 years ago. Used the sun for ... latitude? and a couple of stars (I think Deneb and Arcturus maybe?), a chronometer, and an ephemeris for longitude. We did it on several consecutive nights and days. Anyway, I think that's what we did. I assisted a real surveyor and learned OJT. It was long ago and down north of Barilochi.

B

what's up with that? I'm guessing you are connected there.


does trimble make personal devices? I wasn't looking at surveying grade eq. Just tracking and personal mapping I could do while traveling, wheeling etc... and I guess, in general, finding my way not that I don't love being lost. Compass and paper map are still what i prefer in the wilderness.

I didn't think of ESRI. Used a lot of their stuff for GIS apps. in the past. I'll have to check in on the others.

Thanks

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72 W114/M130

RedMeat cartoon

Its probably not especially ethical for me to mention brand names if people might construe that as an endorsement, with me as a gov agent. Restrictions are especially tight in my agency due its "colorful", checkered past. So if I mention specific brands I don't want folks to think its something official.

Trimble GPS units are the oens I've used the most. I have found them far more rugged than advertised and the tech support is very good. They have a full range from casual to 0.01 meter survey grade. The survey machines have completely replaced plane table surveying (a mapping tool of simplicity and elegance that i sorely miss). I have used a number of different brands of GPS. For general field work and modest accuracy (10-15 meter) there are some good products out there. Garmin makes some very good receivers that are very competively priced. That they undercut better units from other companies and maintain rugged, high quality says an awful lot for the company. Garmin is my favorite general purpose GPS. Racal makes a unit for DoD that is very rugged and very fast. The DoD version uses a different portion of the broadcast spectrum and is not supposed to get out of custodial care. I don't know if they have a comparable unit for civilian use.

I have never used a small Ashtech unit but folks I know like their high-end systems. Several scientists I work with swear by their Magellans. The only one I used was kludgy, but that was years ago and so probably not a fair criticism.

If I were looking for a car-mounted unit I would look for one capable of locking 12 satellites.

Look for one that has user-adjustable horizon masking and multipath filtering. Different companies have different ways of describing these functions. Horizon masking allows you to determine how high above the horizon a satellite must be before the GPS considers it useful. Using satellites low on the horizon introduces refractive errors--like a mirage. Setting it too high will reduce the number of available satellites.

Multipath is a beam-scattering error. The signal is broadcast from a wide antenna. Parallel rays may get bounced-off nearby objects before being picked-up by your GPS antenna. The GPS may get confused as to which signal is the "real" one and so may lock on one that is reflected from some distance. This will degrade your error ellipsoid to beyond the expected 10-20 meters. Metal objects (like a car!) tend to cause the most problems. Set too high and you may filter useful signals and set too low and you'll have a larger than expected error ellipsoid.

Also, look for one that can read several file formats. Don't lock yourself into a single data source. I'd also look for a color display. Monochrome is great for people who have time to think, but in a car you gotta get the message fast.

In all honesty, I rarely use the GPS for road navigation. I find folded or rolled paper maps far superior. A computer screen just doesn't give you context like a map gives you. And its hard to write notes on a GPS screen. Ah, but when you need one, they're really a great tool.

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