What is this?

[IVAZ]

Re: What is this?

Why would they do that with a marine GPS but not my $80 handheld that works everywhere? It doesn't make any sense to me.

Trust me, it doesnt work everywhere. The units that are capable (like the ones on 18 wheelers)are rather big.

 

[IVAZ]

Re: What is this?

Are you sure about that? There are many many times when I get no bar at all on my phone but the GPS still took me to the saved waypoints. My graph acquires 6 (I think) sat signals. For some reason, it can't get any signal while in my garage but my phone gets 5 bars.

The reason is because you have a GPS base station close enough to direct that signal to a cell tower.

 

[Fl_Richard]

Re: What is this?

Thats odd..... My handheald GPS and my $2000 Hummunbird both work 70 miles offshore. Well out of cell phone range.

Cellphone GPS relies on cell towers.

Gotta call a BS alert here!

Any real GPS over $100 will work well out of the range of cell phone towers, they rely on satellites in a geosynchronous constellation orbiting the earth. Trees and yes your garage roof will stop the signals from the satellites.

GPS + WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.

Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.

So yea, 3 meters of accuracy, you boat is most likely 2 to 3 times bigger than the GPS+WAAS error factor. For boating it's fine, for measuring your property line... not not accurate enough.

 

[Bob's Garage]

Re: What is this?

It sounded good upto to a point, then it started to sound like misinformation and supposition.

GPS instructions indicate need 3 Sat. for best signal processing, but can work off 1.

There is no way the GPS works off cell towers, I think you are thinking about the old loran. Those worked off towers, and are now being upgraded (loran-E)to be more accurate than GPS. But they use their own towers.

 

[tmfd]

Re: What is this?

The GPS Unit, unless it IS a phone, does not rely on cell towers but on satellites in space orbiting the earth. Your GPS receiver "locks on" to three or more satellites and figures out your position. It will work anywhere on earth that has access to the sky. C'mon, cell towers??

 

[IVAZ]

Re: What is this?

Thats odd..... My handheald GPS and my $2000 Hummunbird both work 70 miles offshore. Well out of cell phone range.

Cellphone GPS relies on cell towers.

Gotta call a BS alert here!

Any real GPS over $100 will work well out of the range of cell phone towers, they rely on satellites in a geosynchronous constellation orbiting the earth. Trees and yes your garage roof will stop the signals from the satellites.

GPS + WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.

Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.

Before you call BS (which is to late) call any local land surveyor (registered surveyors are required to take classes about GPS) in your area and ask him if your $100 unit works anywhere.

 

[109jb]

Re: What is this?

For the OP. That funny looking thing is indeed the pitot pickup for the speedometer. Many outboard engines also have a pitot hookup built into them. You only need one. As far as the wheel, it is for low speed like trolling. The wheel is acurate at low speed and loses it at higher speed.

As far as Marine GPS using cell towers - NOPE. There are GPS units that use cell tower locations to aid in acquiring the link to the satellites, but as you may have guessed these are mostly in GPS enabled cell phones. Everything IVAZ is saying is basically wrong. GPS works totally off of the satellites. The receiver basically knows how far away from each satellite you are and it knows the orbital position of the satellite itself. If it knows how far from one satellite you are it knows you are on a sphere of that radius from the satellite. If it knows 2 satellites then where the 2 spheres intersect is a circle. If it knows 3 satellites then the intersection of the 3 spheres gives 2 points in space. The reason 3 works is because the software in the receiver deduces that you aren't floating in the middle of space and it ignores the point out in space. That is why you need 3 satellites minimum for a fix. Each satellitle beyond 3 adds to the accuracy because the software in the receiver uses each additional one as a cross check of the others. Also, the geometry of the satellite locations can affect the accuracy and the receiver will chose the "best" satellites to use for the position calculation.

 

[_chris_]

Re: What is this?

Trust me, it doesnt work everywhere. The units that are capable (like the ones on 18 wheelers)are rather big.

I've been using this handheld for 5 or so years in the middle of nowhere on land and in the sea and never been lost so I will at least think to myself that it is working on satelites, or I am suing Garmin for lying to me.

 

[_chris_]

Re: What is this?

This is from the Garmin website.


The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.

How it works

GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.



A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.

 

[Lion hunter]

Re: What is this?

I use GPS (both the handheld and survey grade trimble units) in my work. There is no GPS that requires a cell phone tower to recieve a signal. The Spot system and others can send a signal or distress through a commercial sattelite system which can relay the information to ground based antennas and on to cellphones or e-mail. But does not require them for signal.

In simple terms the only reason for base stations is to recieve correcttion information from the sattelites. This is the reason that survey grade units are more accurate (they can be corrected). Even without correction since the military turned off selective availabilty during the 1st Gulf war the hand held units are very accurate and used by the military. So if you can get a 3d signal on a handheld your pretty accurate in the readings.

 

[LIQUID PROZAC]

Re: What is this?

how did we get from a question of a pitot to comments on a gps on this thread???

 

[Lion hunter]

Re: What is this?

Prozac, you're right. Sorry for adding to the rabbit trail. Guess we couldn't let the GPS thing go.

 

[Huron Angler]

Re: What is this?

how did we get from a question of a pitot to comments on a gps on this thread???

Well I feel responsible since I was the one who opened the can of worms as far as whether GPS, spinning wheel or pitot is more accurate...the dang GPS stuff just spread like wildfire after that

 

[5150abf]

Re: What is this?

When you post something that changes the basic premise of how something works it will get some attention, like saying outboards really run on the water they are in and just use the gas for cooling, most people knew it wasn't right.

We shouldn't dog IVAZ, I have misunderstood things before as most of us have but I think it has been set straight now.

 

[Thad]

Re: What is this?

or I am suing Garmin for lying to me.

Let's make it a "class action". Then we all get rich quick
tchpet2, so are you gonna hook it up or not?

 

[smclear]

Re: What is this?

While I believe that the pitot tubes are generally not especially accurate, I have to say that I have one on my boat that actually matches my handheld GPS at every speed. Still as a general rule of thumb, I'd still say that the pitot tube style is less accurate on average than GPS.

 

[mmccoy555]

Re: What is this?

It all depends on what you consider accurate. The GPS speed is measured over ground which doesn't take into account the wind and current like the one on your boat does. you could be going 4knots through the water with a 1knot current and your gps will 2 or 3 knots( just as a weak example).

 

[gonefishie]

Re: What is this?

What???

 

[allinmygarage]

Re: What is this?

Hey I might be able to help with the cell phone / GPS / Cell tower part of this thread that has spun out of control

My cell phone has a built in GPS and will get pinpoint my exact location anywhere in the world .....HOWEVER.......it uses a cell signal to download the corresponding maps. In other words my work or whomever can pinpoint and tell me where I am but I may not be able to see it on my phone unless I have a cell signal. Most phones do not have the memory / storage availible to have all of the maps so they rely on things like Google maps and GPS technology to pinpoint your location.

Figured I would add something to a thread that started with a simple speedometer question

 

[witenite0560]

Re: What is this?

I've checked my pitot speedo against my GPS and the speedo actually is accurate to within about 2 - 2.5 miles per hour once I'm above about 10 miles an hour. Below 10 the speedo doesn't register.

BTW, that's the same handheld low budget GPS that I've used all over the U.S, at 40,000' over the Atlantic and in SWA.