My first GPS receiver was an 8 channel model that monitored each channel (each satellite) in sequence. Years later, 12 channel models appeared, and they monitored the channels simultaneously, and I have a few of those. They also added WAAS. Their accuracy is much better. Along the way, Selective Availability was switched off, making them better still. Now with a good view of the sky and good satellite placement, they report 12 channels received, and the 11 that are not the WAAS signal are being corrected by it. They give a horizontal accuracy of five feet at one standard deviation.
But these things appeared maybe 10 years ago. I haven’t seen any advancement at all in the GPS engines for little consumer receivers since then. To be fair, the makers haven’t been idle - they made versions that work way better for car navigation, with maps and route calculation and big color screens, one of which I have. But this is a change in the user interface, not in the measurement of position. Is there any progress in the engines themselves?
Well, cellphones use AGPS. I believe (but don’t know for sure) that the way AGPS works is that the cellphone first queries whatever cell tower its connected to and the cell tower tells it approximately where it is (I think by telling the cellphone exactly where the cell tower is) and which satellites to look for.
I believe the net result is that the cellphone gets a quicker initial lock on its location. My standalone GPS unit would sometimes take several minutes to achieve its initial lock, but my cellphone’s GPS unit starts working with seconds of when I first enable it.
AHA! I found a website that describes AGPS (what it does, how it works).
I guess we are close to reaching the limits of actually locating a point (5 feet seems good enough for most uses). Probably the GPS makers are putting more effort into making better maps, providing some location aware information and so on.
I saw an app for an iPhone that was kinda interesting. If you held it like a video camera, and pointed it down the street, information bubbles (name, address, phone) would pop up above the buildings as you panned around.
The picture was the actual real time video from the camera.
There are limits to the accuracy you can attain without using high-end (and highly expensive) survey-grade GPS equipment. In order to pin down a location, we use 2 GPS units, one at a known, fixed location, and one roving. The rover and stationary units communicate by radio to establish your position, using the known location to correct the position of the rover. Without that setup, even my $25,000 rover unit will only get me within 5 feet or so.
These aren’t precision improvements, but they’re not really merely UI changes either:
Real-time traffic updates and sometimes automatic reroutes based on them
Mobile broadband connectivity to look up businesses and reviews on the road. The Dash units did this in one integrated unit, but these days I think that functionality is found mostly in smartphones
Dead reckoning (estimating your position when you lose GPS signal based on your last-known position and current direction/speed, e.g. when you go through a tunnel) may have become more common
With Android phones, you can get Street View for any particular point of your route. As you approach your destination, it automatically switches to Street View so you know what you’re looking for. There’s also an app similar to what enipla described that overlays your route on top of a real-time view of the road ahead (through the phone’s camera), but initial reviews weren’t great.
SurveyorAlpha, this is the kind of thing I’m interested in. I’ve done some work with postprocessing, using a program from DeLorme called “PostPro”, and two kinds of receivers they made that recorded the pseudorange and carrier phase information. I’ve also used these with CORS datasets downloaded from the web, and even made friends with the staff of a nearby sewer plant where they happen to host a CORS. These DeLorme products are amazingly buggy and barely work - can’t get the information from the hardware to the PC, have to go in and edit the text datafiles because the dates are written wrong, have to edit together blocks of text that get separated, and so forth. But I did get these things to work, and wrote my own least squares program to regress my net of stations and monuments, combining total station and postprocessed dgps readings.
But it was such a mess due to the buggy hardware that I kind of gave up on it, at least for now. I have some Garmin OEM receivers that can work in a binary mode to give this kind of data, and I wrote code to parse the structs they define in their docs and actually started digging in to how to do my own postprocessing, but it was complicated enough I also gave up on that for now.
You’d be amused to hear that my $150 Garmin GPS-60 handhelds (I have 4) can give locations that repeat to within about an inch and a half (one standard deviation) if I let them do waypoint averaging for weeks at a time. I did this with remote antennas attached to my roof. I am pretty sure that Garmin cheats and uses the least significant byte or so of their 32 bit integer internal representations of latitude and longitude to encode some other damn thing, like what goofy symbol to use to plot the waypoint, if you get the receiver data using their software; I have to use G7TOWIN software to not mess the waypoints up (the receiver displays only read out to about 6 feet).
Seems like there’s a nice little niche for a consumer product here. Some lucky entrepreneur could make literally thousands of dollars with only a few years work. Anyway, I was looking for ways to feed my tinkering…
My old (but less than 10 year old) Garmin Legend handheld is slower to locate itself after power up than my newer (2-3 year old) Garmin Legend HCx. It’s also slower drawing the screen. The newer unit is also able to get a usable signal inside my house, while the old one cannot. So the biggest improvement to a newer unit is a faster processor and more sensitive receiving antenna. It could also be that the faster processor makes separating a weak signal from noise easier to do, rather than an improvement in the antenna.
The old unit can be setup to output its data in NMEA format on a serial port, the new one just speaks Garmin’s own protocol over USB. I see that as a step backwards, which is why I keep the old one around.