DGPS - Differential Global Positioning System

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LandCruisers4Life said:
If you look at many wheelers rigs in remoter areas of the world such as Australia, they have their own DGPS going on. Ever wonder what all those antennas were for on their bull bars? Not just radios that's for sure.
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Dreaming mate, there's just about no DGPS in oz, and basically none in the bush. No need for it out there - if you can't figure out where the heck you are within a few 100 metres - you've got more problems than being lost :)

Yes, all those antennas etc on the 4wd's there are radio. UHF is typical and a lot of folk run a HF antenna for the flying doctor etc.

cheers,
george.
 
Serious radios then!!
 
bhmmapping said:
that is not a good analogy. If they replaced regular GPS for civilians with something as or more accurate that was even easier to use and required less investment, then I would be mad if they kept pushing funding for the regular gps over the new and better alternative.

I can understand if you have an investment in DGPS, but I don't think there is any advantage to it over WAAS for inland wheeling purposes and I wouldn't want someone to go out and spend the extra money on a DGPS system when they don't need it.
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WAAS is not a replacement for DGPS, it is inferior.
 
That's your right. All evidence points otherwise. Including in field experimentation by myself and friends who have WAAS equipped GPS units.
 
You guys are killin' me:)

I suppose this all depends on one's definition of "inferior." An inferior solution is inherently inadequate for one's needs. Maybe LandCruisers4Life and bhmmapping define needs differently.

As more than a casual observer I will make the following observations:

1) WAAS, EGNOS, GAGAN, MSAS, and to a lesser extent QZSS and Beidou 1 are regional augmentations that provide value to users at little or no cost and do not require the purchase of additional kit. All of these systems do require that manufacturers of GNSS (GPS on steroids) receivers incorporate these systems' interface control documents (ICDs). In general, by definition, regional augmentation systems do not work well at the fringes of their ranges. As case in point is WAAS. Its iono modelling is crap at the western edge of the US and the eastern edge of the US because it has no receivers in the Pacific or Atlantic with which it can derive the iono measurements (for you geophysicist and atmospheric scientists out there I know this is a gross simplification). As a result the models of the systemic errors in the system that are sent to your ground based receivers are inadequate at the fringes.

2) DGPS will "always" be better than a wide area system until precise point positioning solutions are able to resolve ambiguities (sorry about the techno babble). In short, this is because a reference station calculates the systematic and intentional errors in the system and transmits them to the mobile unit. The down side to this of course is that the user must buy additional equipment, be in a "closer" proximity to the reference station, and potentially have to buy a more sophisticated receiver (ie., more expensive), or pay for the service.

3) There were some comments made earlier about not needing greater than 100 meter horizontal accuracy. In the majority of cases I agree. However, I have been in many cases in low visibility conditions where I was very happy to have sub meter positioning.


So, in short, you are both right (IMHO):)
 
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You might need that accuracy..... especially if your eyesight is as good as that dogs in your avatar!
 
LandCruisers4Life: Thanks for starting this thread and sharing the info (et al too). Not knowing anything about GPS technology it is interesting to read/learn nonetheless.
 
This thread is turning into another 3 ring circus...... I'm trying to keep it from doing so however! :eek:
 
Not to piss on a beehive or anytyhing,

but for general offroad use, when is it that you find better than 10-meters to be important?

In my limited experience, there have been times when I've used the gps to find my way in everything from downtown Guatemala City to the plains of Idaho to the mountains of Costa Rica. But I've never found myself thinking "I think I'll keep going west because the GPS says I'm still 20 feet from the river"

Again, I'm not trying to belittle your position. I remember getting in an argument with a backpacker in Monteverde, Costa Rica seven years who thought I was effete to even have a GPS unit instead of just relying on a map and compass. I just haven't ever seen the need for greater accuracy while driving and am wondering what sort of situations you have found that do require/benefit from the increase in resolution.
 
Under 'normal' circumstances, regular GPS is fine. However under circumstances where weather, ionic disturbances etc occur, the DGPS system helps to keep you within normal bounds by correcting for errors/abnormalities..... that is where I am coming from.
 
I have been lightly following this thread and agree that the enhanced accuracy of DGPS is not needed in off-road or recreational boating. The high accuracy has been developed for use in surveying and vessels that rely on GPS for dynamic positioning. I'm sure the military has a stake in it too.

GPS is fun and easy, but try not to rely too heavy on it. I have been aboard vessels on more than one occasion where the old LORAN or GPS signals we received were inaccurate, mostly because of equipment failure on the vessel. All GPS systems warn you at start up not to rely solely on their device.
 
Hence.. 2-3 GPS units in your vehicle :D
 
Some people can read maps, and some can't. I can read a map just fine. This thread isn't about MAPS, so either stay on subject or go post somewhere else.
 
dgps is starting to sound a little bit like MIBS

telling people to scram when they point out a perfectly valid point isn't friendly.

While traveling all over Central America, I considered our gps to be almost a necessity... I don't know if I relied on it, per se, but I certainly learned to enjoy it. Having said that, every day before starting out I'd look at the best map I had of the area where I thought we would be driving, and every day after we arrived (almost every day, anyway) I'd mark on the map where we had driven.

All that mapping was redundant to my gps/computer... but I just like to know where I was w/regards to big landmarks, the ocean, towns, etc so that I didn't rely to heavily on the gps. Besides, maps are pretty and I like to run my finger along a given route, or jump miles and miles ahead to see something else. I've never enjoyed the experience as much with screen. It's a little bit like reading a book vs. reading online. Online is fine for a forum, for example, but give me a paperback (please!) if it is over 2 pages.

For me, personally, carrying a second (or third?) gps isn't cost effective. I'd prefer a map and compass for that, as they are less fallible than a 2nd gps (and what if the problem is the satellites or the system, and not my gps unit? ).

I suppose that if the price of the gps was lower (or my discretionary gadget budget higher) I could justify one full-color, snazzy gps unit, hardmounted to the rig and another, handheld unit for when I'm not in the truck.

Anyway, just thinking out loud 'cuz I really don't feel like attacking the stuff on my desk right now.
 
I have seen some pretty impressive dual frequency GPS kit from Leica Geosystems for surveying but I am not up enough on the technology to know if it is a subscription based service or something that would be applicable to this scenario. However being able to derive your correction from a satellite based signal seems like it would have a much wider application than ground based stations.

For land navigation with visible landmarks and the option of waiting out inclement weather I see no argument for "needing" a highly accurate GPS location as it is a solution to a non existent problem. For sea and air navigation where there may not be visible landmarks and no option to wait out inclement weather a higher level of accuracy is needed and as already posted the ground based DGPS systems that are in place for sea navigation seem to be fully funded. Additionally I am sure that advances in technology are going to render the ground based DGPS system as relevant to GNSS as wooden block printing presses are to publishing today.

In the end you can have a GPS system that is accurate to +/- a few centimetres and a map that is using a different geodetic reference system than your GPS system and that +/- a few centimetres accuracy is useless anyways. At that point it is up to the user to determine if they are going to rely on a map or the GPS system.
 
You should always carry a map, or maps, and compass. I only said what I did earlier to NorCal Cruiser because of the way he came off being sarcastic.
 
jasonmt said:
In the end you can have a GPS system that is accurate to +/- a few centimetres and a map that is using a different geodetic reference system than your GPS system and that +/- a few centimetres accuracy is useless anyways. At that point it is up to the user to determine if they are going to rely on a map or the GPS system.
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Might be useless, unless you have been to where you want to go and have your own coordinates etc. Sometimes we have to make our own corrections on maps according to what our own information tells us.

Valid points however, thanks for contributing.
 
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