What GPS?

[Hoosier]

I assume what you’re talking about is a hand held consumer GPS unit.

I am a licensed land surveyor in California. I have been using GPS equipment since 1992. I’ve owned and operated all sorts of systems from really cheap hand held units to high-end, survey-grade systems. I’ve used equipment that could only receive American NAVSTAR signals and systems that could receive both NAVSTAR and Russian GLONASS.



All models do the same basic job. The extra dollars buy more features. The key is to figure out what you need and what you can live without.

Great overviews... Thanks.

So, what is your recommendation for the diver?

 

[BKP]

First, why a handheld? They're great for hiking/camping, however, if you can mount one in a dive boat (even temporarily), you're better off with the larger screen/higher function models (budget permitting).

I used a Garmin III for years. It was meant for land-based navigation, but, worked well on inland waterways, on my boat, with an excellent "Tracback" function (trail of electronic breadcrumbs to return route), waypoints, routing, etc. That was YEARS ago...

If you're going open water, you'll need something that can map it, like a Chartplotter function. Doesn't have to be big $$...

Take a look at the Garmin GPSMAP 376C... Gives you route plotting (land and water), as well as satellite weather... big plus... Has an IPX7 rating which means you don't have to worry 'bout it getting wet/splashed (doesn't mean you can dive with it).

You can get it street priced for around $750... or, if you don't need the weather, you can get the 276C at around $600...

(No, I don't work for Garmin... just a satisfied user...)

 

[fabasard]

Handheld are good for a number of reasons, including HIGH portability, great quality, ruggedness and fairly low price. Just about any GPSr will do the trick for your BASIC needs, in that you want to mark a location. Also good for tracking how you got there. I use the Garmin Vista and its a FINE machine, although I want to upgrade to the VISTA CX. You can get a garmin legend I think (the cheap yellow one), and it goes for 50-100 dollars. It will store waypoints, and let you route back to them, and since your on the water you don't have to worry about following a path (for the most part). Most of garmins products state that they are water resistant (from their website "can be submerged in 1 meters of water for 30 minutes"), handy considering the wetness that is inherant with diving. You COULD pay more for a better model, but then you worry about it being stolen, dumped overboard, any number of problems. For your concerns, OP, I suggest a cheap GPSr, as cheap as you can get away with. And its true, no GPS works underwater, although I have heard some theorize an antennae at the surface with a line to the GPS below (too much hassle). Good luck, Fabasard

 

[ianw2]

So, what is your recommendation for the diver?

Well, I highly recommend my wife. She’s a great dive partner. I’d also recommend diving with Grateful, TS&M and a bunch of others. I think they would be blast to dive with!

Oh! You mean a GPS unit for divers!

I use a Magellan Color. It runs about $300 with the extras and maps. I’ve used it all over the world. I like collecting way points on our trips. It’s relatively hardy - it stands up to my fumbles and bounces. It works of two standard AA cells (I use rechargables). In a GPS dry pouch, its been out in everything from the MS Elation to the Bottom Scratcher to a kayak. I’ve even had it in the water (surface only) with me.

Of all my hand held units, it’s survived longest with me. I’m rough on gear.:shakehead

why a handheld?

Well…mainly because SteveC posted:

Anyway, I'm looking to purchase a handheld GPS for diving

A boat based GPS receiver would also require having a boat to mount it in. That would significantly increase the cost of the unit if he wasn’t already a boat owner.

I have heard some theorize an antennae at the surface with a line to the GPS below (too much hassle).

Not to mention that any distortion in the line down would create significant error in the location. Having said that, I’ve given serious thought to popping my unit (in the dry pouch) in the SCUBA float and towing it on the surface. That way, I could log way points for features on the bottom that I wanted to find again.:11:
.

 

[Spectre]

I got a Garmin 60Csx for Christmas and have used it for geocaching. It is a great unit, but I think you can get decent units cheaper. Mine will take land and marine maps. I haven't used it on water yet, but I get 10-15 foot accuracy.

I went shopping for a unit last summer and decided on the 60Csx. Since that time, two of my buddies got the same unit [one replaced his Magellen with it].

The only nit I've found is occasionally it gets confused when I have both topo and street maps loaded up. It once tried to take me across the Millpond in Marianna to get to Edd's shop; but aside of that, I love the thing.

One of my buddies determined it's the perfect size to fit into a light canister; which is going to allow us to get numbers for some sinks we've found underwater but not on the surface.

 

[jeffrey-c]

WAAS is a system of ground based transmitters in North America that correct slight errors in the satalite signals. You need to be in a WAAS area with a WAAS enabled GPS for it to work. Europe has a similar system, EGNOS or something like that.

A slight clarification: WAAS uses a system of ground based receiver stations in the US that determine a correction signal which is processed and transmitted over two of the INMARSAT satellites, covering all the western hemisphere and eastern Asia. Other satellite-based systems are EGNOS (European Geostationary Navigation Overlay System) in Europe and MSAS (Multi-functional Satellite Augmentation System) in Japan.

An earlier-developed system called DGPS (Differential GPS) uses a series of land-based transmitter sites that transmitted a beacon at 300kHz. For DGPS, one has to be in the range of the beacon sites to receive the signal; beacons were set up pretty much covering the east and west coasts of the US plus the Great Lakes; I'm not aware of much other DGPS coverage. Both DGPS and WAAS are technically differential GPS systems as each system transmits correction signals which are processed by the GPS receiver to correct, however the terrestrial system is typically referred to as DGPS. The WAAS signal is transmitted on the same frequency as that received by GPS receivers, meaning the antenna and RF tuner are the same and only demodulation and signal processing are needed; this reduces the cost of the WAAS system compared to a DGPS receiver, which also needs a whip antenna to receive the high frequency DGPS signal.

I've have both DGPS and WAAS in my boat, and the accuracy for each seems equivalent. The GPS built into my car also uses WAAS - it's uncanny how accurate it can be!

 

[ChrisEdwards]

I have an old Garmin Street Pilot III, that I used to use in my cars, but still use in my RV as all my existing cars have factory Nav systems. Compared to the factory Nav systems I've used my Lexus, Mercedes and Cadillac, only the Lexus was better than the Garmin unit.

I also have a Garmin GPSmap60c which I use on my motorcycles or hand carry when hiking. It does just about everything that the more Auto oriented GPS units do, plus it has tracking capabilities. If you venture off into woods or unknown terrain, the GPS can be set to take a track point either by distance or elapsed time. I have mine on 15 seconds. This way it builds a track of where you have been so you can always back track.

I use this feature quite a lot when dirt biking. It lasts two or three days on one set of AA batteries. It can also be powered from either a car or motorcycle battery.


The PC software for loading the map data into the GPS unit is very easy to use.

I have no affiliation with this company other than this is where I have purchased my last three Garmin units www.gpsnow.com

 

[ianw2]

I've have both DGPS and WAAS in my boat, and the accuracy for each seems equivalent. The GPS built into my car also uses WAAS - it's uncanny how accurate it can be!

Accuracy is relative, too. Accuracy to within 10 feet is outstanding for use in drive to places. That kind of accuracy for me as a land surveyor would put me out of business in a heartbeat!

You’re correct, WAAS is a "free" DGPS service. It works by having ground based receivers on fixed, known points on the earth. The correction broadcast is based on the difference between the positional fix for that epoch and the known position. Since there are many other variables in the equation, the correction is only valid for a limited area and to a limited accuracy.

There are a number of subscription services that cover significantly smaller areas and require units with additional radio frequency reception capabilities. The old Trimble Pathfinder I used was accurate to within half a meter when I could get signals from the correction service. That was more than accurate for photo id in photogrammetry.

The survey grade Topcon HiPer Lite system I use is also a DGPS system. The base station also broadcasts correction vectors for use in a very limited area (with a 5Km radius). Because many of the variables are removed by having base and rove close together, the accuracy of this system is boosted to sub-centimeter. That’s accuracy I can use as a surveyor.

DGPS techniques were developed back when the military would scramble the signals from the satellites and dilute the quality so that the positional accuracy was something on the order of +/- 100 meters.

Unfortunately, the conditions are poor here in So Cal. So, instead of diving at the Marine Room at La Jolla, I have to haul myself into the office and head out to the field to use my Topcon system to collect topographic data for a parcel split. Hopefully Saturday will be better….

 

[ianw2]

One of my buddies determined it's the perfect size to fit into a light canister; which is going to allow us to get numbers for some sinks we've found underwater but not on the surface.

I will be very interested to see your results.

First, without having the unit in the housing, get 5 or 10 points over a large area…say 2 or 3 miles. Mark the points so you can come back to them accurately.

Then, pop the unit in the housing and try to go back to the points. Record the differences. This will be errors generated by having the unit inside a housing. The housing will shield your unit from the satellite signals.

Finally, see how the unit does in the housing at the surface, at 10 FSW, 30FSW, 60FSW.

I’d really like to see the results. If you manage to get good data, I’ll pass it on to Jan van Sickle, a noted authority on GPS technology and use.

Cheers, Spectre!

 

[airsix]

My short & sweet recommendation:

Get a unit that will let you add maps via upload or better yet a memory card. The built in maps are marginal at best, but the add-on maps are usually very good.

I love my Garmin by the way. It's been a workhorse for 4 years now and never gives me a lick of trouble.

-Ben M.