Any GPS experts here?

[A Visitor]

Thanks everyone for the feedback - I think I will go for it and report back on my experience in case anyone is interested...

 

[TromboneAl]

Yesterday our refurbished Garmin 340 arrived. Total with shipping: $85. A little bigger than the newest ones, but that's not a problem. Schwarzenegger won't let us mount it to the windshield, so I'm trying to find a good mounting option that doesn't involve gluing that disk to the dashboard.

It works great. I'm totally blown away by this technology.

We got it for our upcoming trip, but I realize now that the best application is finding garage sales. All those times spent looking up a street name on the map, then finding it in the AE18 square, getting carsick...[FONT=verdana,arial,helvetica][SIZE=-1]

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[Notmuchlonger]

We have a Nuvi 660. The thing has been great on our road trip. I however still carry a map. Old habits hard to break.

 

[Gotadimple]

Yesterday our refurbished Garmin 340 arrived. Total with shipping: $85. A little bigger than the newest ones, but that's not a problem. Schwarzenegger won't let us mount it to the windshield, so I'm trying to find a good mounting option that doesn't involve gluing that disk to the dashboard.

It works great. I'm totally blown away by this technology.
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Try the GPS Store (thegpsstore.com). I currently looking to upgrade my map software for my nuvi and looking for a different mount than the windshield.

And you're right, while great for a long trip -- they're the best around town!

-- Rita

 

[tmm99]

I have a Garmin. It was a Bday gift. I glued the round thing to the windshield (CA law changed in Feb this year allows the GPS to be mounted in the tiny corner of the windshield), but the device falls off after about 5-10 minutes. The suction thingy doesn't seem to work all that well. (I was hoping the round thing glued to the windshield would help, instead of directly attaching the sunction cup to the glass, but it didn't.)

Any suggestions?

tmm

 

[Gotadimple]

The trick with the suction mount is to make sure that you are firmly pressing it to the glass before you flip the suction lever. I've failed to do that and it dropped unexpectedly.

Don't know anything about the round disk.

-- Rita

 

[smileydog]

I have two magellan units one 3100 and one 4250 both work well and I recently updated the firmware on both (free upgrade). I have no complaints except for the occational new road that isn't on the map but that is pretty rare. There is a paid map upgrade that I may consider getting that is about 45$ that could fix some of the new road situtations.

I've always heard the the Nuvi was a better unit but a recent trip when a friend and I both brought our gps units - both worked almost identically. I sure could not see any obvious advantage of one over the other.

 

[A Visitor]

Well the Magellan 4350 still has a MSRP of $400 so the 40% discount to $240 looked good, but Amazon now has it for $235 so I'm waiting to see if the MSRP comes down...

 

[Texas Proud]

I bought a Tom Tom (cheap) and it has not been great... may times it refuses to plot a path to the destination until you get closer... it has frozen a few times and had to be reset.. it also wants to take you down side roads that can NOT be the fastest way even if you tell it you want the fastest way... tried to update the map and software and got errors that the map was not registered (and it will not let me register it even though I have the proper codes)... very disappointed... but it DOES work about 75% of the time so we still use it at times..

Got a Garmin (bigger screen... as someone said a little bit more screen makes a world of difference)... because the wife needed something more reliable.. have not had a problem with it at all.. I have not tried to update the program or the map as they did not give you a connection to the computer with the unit and I am not willing to pay for one... it is slow to pick up the sats... but so was the Tom Tom... this can be bad IF you do not know where to go from the start... you just sit waiting to get the signal and sometimes wait for 10 minutes...


One 'flaw' in the Garmin is that it 'thinks' you are at the location you last turned it off... so if you turn it off in Austin and back on in Houston, it thinks you are still in Austin until it gets the sat signals... but I guess that might be the same for the Tom Tom, not sure...

 

[REWahoo]

I do not trust the accuracy of any of the GPS devices. Since I'd end up verifying what it told me against a paper map, might as well save time and money and just stick with the map.

My fear is to be "Garmined" down the wrong road in our RV and end up with and unwanted haircut...

 

[bbbamI]

Ouch....

 

[TromboneAl]

CA law changed in Feb this year allows the GPS to be mounted in the tiny corner of the windshield

Good to know, thanks.

Next question: Burglary. Is someone likely to break into my car if they see a GPS mount or even the GPS device? (I've stopped worrying about someone breaking in to get my crappy tracfone.)

 

[TromboneAl]

The other useful feature I've discovered is that it estimates when you'll arrive at your destination. That's good to know if you have to be somewhere at a specific time.

Anyone figured out the algorithm it uses?

• Uses speed limits?
• Takes into account your current speed?
• Takes into account your current speed in relation to speed limits?

 

[Sam]

The other useful feature I've discovered is that it estimates when you'll arrive at your destination. That's good to know if you have to be somewhere at a specific time.

Anyone figured out the algorithm it uses?

• Uses speed limits?
• Takes into account your current speed?
• Takes into account your current speed in relation to speed limits?

My Garmin GPSs have that feature as well. Unfortunately, it's totally useless. The method use is not documented in the manual, but my observation says that the current speed is use.

Sam

 

[Sam]

I do not trust the accuracy of any of the GPS devices. Since I'd end up verifying what it told me against a paper map, might as well save time and money and just stick with the map.

REWahoo, the accuracy (and sensitivity) of today's GPSs are approaching perfection. It's the mapping data that gives the impression of inaccuracy. Keep in mind that roads change, new roads are added daily. Those changes/additions have to find their ways into the GPSs, and that is accomplished by yearly software update.

In my experience paper maps are way more inaccurate than GPSs, and their costs are sky high. I can update my Garmin mapping data for around $50, and that includes every street in the US and Canada.

For me, the only advantage of paper map is the bird view. I still carry an 5 years old road atlas for that purpose only.

Sam

 

[Sam]

One 'flaw' in the Garmin is that it 'thinks' you are at the location you last turned it off... so if you turn it off in Austin and back on in Houston, it thinks you are still in Austin until it gets the sat signals... but I guess that might be the same for the Tom Tom, not sure...

I look at it as a feature more than a 'flaw'. By remembering the last location, the GPS can focus on the satellites it last saw so it can get back on line quicker. My Garmin 60Cx and V have the option allowing you to tell the GPS to forget its last location (Satellite page, Menu, New Location.) It might be available on your Garmin model too.

Sam

 

[W2R]

Good to know, thanks.

Next question: Burglary. Is someone likely to break into my car if they see a GPS mount or even the GPS device? (I've stopped worrying about someone breaking in to get my crappy tracfone.)

As a resident of the New Orleans metro area, with our huge crime problem, I think I am highly qualified to answer this question.

Someone is likely to break into your car if they see ANYTHING in it, much less a GPS mount or device. I don't even leave my lunch in my car. People who break into cars are often high as a kite and looking for anything they can sell for drugs.

 

[Martha]

Good to know, thanks.

Next question: Burglary. Is someone likely to break into my car if they see a GPS mount or even the GPS device? (I've stopped worrying about someone breaking in to get my crappy tracfone.)

I leave the mount in place and just snap the Garmin unit out of the mount and stick it in my purse or hide it out of sight.

I generally use the suction cup mount on the windshield. It works well except I have noted that if you put it on a below zero windshield it might release as things warm up, even if you take care to make sure all is clean and you press it down hard. Otherwise, I have had it on from Minnesota to Texas with no problems. Minnesota and a few other states don't allow windshield mounts so I have also mounted it on the dash, with the little circle mount. That mount works as well as the windshield. The disc seems unobtrusive.

I have found it accurate but it doesn't always pick the best route. One thing that is helpful is that you can put in a number of GPS units what type of vehicle you are driving or if you are walking. If you put in RV or truck you avoid those low bridges.

 

[HFWR]

My GPS is programmed accordingly...

 

[NW-Bound]

Amazing how far [-]satellite navigation[/-] GPS has come. Early seventies on board the research ship RV Vema, we had an antenna mounted on top of the mast, sucker weighed about 80 lb, had radials and a vertical sticking out of it for 3 feet. The receiver was 19" rackmount classified device with seals on it. With all sorts of rules on who can see it.

The pre-rocessor was another rackmount with about 40 plug in cards with discreet transistor flip flops, outputting data to a Freiden tape punch. Which produced typically an 10 foot long tape with holes in it representing the satellite orbit, ID, time etc.

To actually get the data, the receiver's speaker was always on. THe watch standers in the electronics lab had trained ears for the faint whistle, of the satellite coming up the horizon. When heard the nearest tech would leap to the control head and press the oscillator tune until the local oscillator matched the satellite doppler, and lock onto the signal. Then the receiver would track the doppler shift until the satellite disappeared over the far horizon.

During the satellite pass the Frieden punch would be clankin out the the punched tape with the satellie data.

At this point all we knew was that we had sat. data.

Now came the processing part. The good old DEC PDP8 with 2 Kilobyte of memory was standing by, or running some other program. We set the toggle switches on front panel to tell computer that it is to expect a program. Now, feed the program tape int the reader, hit the go paddle (switch), and the machine would read a punch tape with the proper holes, which had the satellite navigation program.

This completed, the PDP 8 would beep,indicating it was ready to accept data. Now we loaded the previously punched data tape ftrom the last satellite pass, hit the go toggle, and for 20 ro so minutes be rewarded with an entertaining sequence of flashing lights on the front panel as the computer was processing the data.

At the end of twenty minutes or so the winking blinking lights would stop for a moment, then the computer started to output the fix (our location) on a teletype machine. with a great amount of clanking.

THus we received four lines of data with latitude, longitude, confidence level and estimated time of next satellite pass. The fix was typically good for a 10 to 12 mile radius.

After all this we walked over to the chart table and plotted our location. And got on the intercom to the bridge and read them the fix.

Anyone for the good old days??

I now have a laptop in my suburban with Street Atlas, a surplus Rockwell GPS receiver, a puck antenna on the roof and can navigate on the go.

I like this newer version better.

What you described was the predecessor to GPS, called the Transit Doppler system. It dated back to the early 60s, hence was before my time. In the early 80s, I worked in a research group at a major aerospace company. We built one of the early GPS receivers, that had the form-factor of the 19" rack that you described. The full GPS constellation wasn't up, and we only had signal coverage for testing a few hours a day. By the way, the full satellite constellation was not up until the mid 90s, about the time of the first Gulf war if my memory is correct.

The technology was such that the GPS hardware could be built onto a couple of chips 10 years ago. However, without a cheap LCD display and memory for the map storage, GPS by itself is not too useful for civilians. What good is it to tell someone his geodetic position (latitude, longitude, and altitude)? You would still be lost without a paper map or a map display!

 

[NW-Bound]

I look at it as a feature more than a 'flaw'. By remembering the last location, the GPS can focus on the satellites it last saw so it can get back on line quicker. My Garmin 60Cx and V have the option allowing you to tell the GPS to forget its last location (Satellite page, Menu, New Location.) It might be available on your Garmin model too.

Sam

There are currently 32 GPS satellites orbiting the earth. To get a position fix, a GPS must lock onto signals of a minimum of 4 satellites to solve for 4 unknowns: 3-D position and time.

Note that although the GPS receiver has an internal clock, it is not accurate enough as each microsecond of time error is equivalent to 1000 ft of position error. If you carry your own atomic clock, you don't need 4, but only 3 satellites to do a position fix by trilateration.

Now, when first turned on, how does a GPS receiver know which satellites in the set are visible? I should note here that the satellites are not stationary but circling the earth about twice a day.

By assuming that the position has not changed since it was turned off, the GPS receiver would try to acquire the satellites that SHOULD be receivable at THAT time and at THAT position on earth. This default policy works 99.9% of the time. But when the receiver has been moved a sizeable distance, it would try to acquire satellites that may be simply on the other side of the earth.

A GPS receiver always has a backup mode called "cold start" or "cold search" that is entered if the "assumed visible" satellite set cannot be received after a certain timeout. This timeout period can be avoided if the user helps it along by forcing the cold start manually, or to give it a rough initial position. The initial position does not have to be very accurate, as it is only used to decide which satellites should be above the horizon for the GPS receiver to tune to.

And then, depending on the hardware/software sophistication, each GPS receiver has a different "cold start" acquisition time.

 

[Rich]

I've been using GPS units now for around ten years or so. Rarely even look at paper maps anymore, except when I want the "big picture." Accuracy is remarkable (most of the time). Been using Garmins, no opinion regarding other brands.

From what I've observed the sweat spot (most bang for the buck) seems to be around the $200 dollar range these days.

Rich

 

[TromboneAl]

I leave the mount in place and just snap the Garmin unit out of the mount and stick it in my purse or hide it out of sight.

In the old pull-out radio days, I heard a crook say that if he saw a pull-out radio slot in a car, he knew that the radio was hidden in the car somewhere -- most people get tired of taking it with them after a few days. However, a GPS is a lot smaller so maybe this strategy is reasonable.

Thanks for the tech info, NW. Here's a question:

The unit calculates distance from a satellite based on the time it takes the signal to arrive. The signals travel at the speed of light, so a distance change of 50 feet involves a change in signal delay of less than 53 nanoseconds (1/186,000 = 5.3 microseconds/mile. 50 ft = 1/100 of a mile). Am I understanding it correctly?

 

[kumquat]

The other useful feature I've discovered is that it estimates when you'll arrive at your destination. That's good to know if you have to be somewhere at a specific time.

Anyone figured out the algorithm it uses?

• Uses speed limits?
• Takes into account your current speed?
• Takes into account your current speed in relation to speed limits?

Since my Magellan unit makes the estimate before I've started moving, I'd guess speed limits.

 

[NW-Bound]

The unit calculates distance from a satellite based on the time it takes the signal to arrive. The signals travel at the speed of light, so a distance change of 50 feet involves a change in signal delay of less than 53 nanoseconds (1/186,000 = 5.3 microseconds/mile. 50 ft = 1/100 of a mile). Am I understanding it correctly?

Yes. Same as I wrote earlier, 1 microsecond=1000 nanosec=1000ft (roughly).