Hang on there, partner. The GPS system is NOT going to change anytime soon. The accuracy enhancements that you’re talking about, like second and third civil frequencies, broader PRN spreading (faster chipping rate = higher accuracy), and enhanced navigation message are all part of the GPS Modernization Initiative, which currently has not been even awarded. All of the major players are involved, with a contract award forthcoming in the next year or so and a fielded constellation NO SOONER THAN 2010 that contains the aforementioned upgrades.
Most of the accelleration of GPS space programs has been with respect to the IIR and IIF birds, the civil enhancements (I believe) are part of the GPS-III initiative. There’s a pretty good write-up about it here:
http://gps-future.com/mod.html
In addition to that, the L2 & L5 civil frequencies require that vendors make a great many changes ($$$) and the units themselves contain significant hardware ($$$$). All that cost will get passed on to you as the end buyer. For the most part, I would expect that 99% of civil users will still be using a single-frequency unit, and that the additional civil frequencies will be more heavily used by airborne users willing to cough up the extra dough.
Since the modernized constellation is projected to be backward-compatible, your GPS should still be working when we’re all driving to the river in our Jetson’s flying cars and telecommuting from our boats!
You can’t move away from the ‘triangulation’ method of computing position, as there is no other way to do it using GPS alone. Furthermore, all units will offer basically the same accuracy regardless of what they advertise. The majority of the errors are in the constellation and signal disruption in the atmosphere.
There is a lot of work being done right now with miniaturized inertial sensors (MEMS) in the automotive industry, which will greatly improve GPS performance in an urban-canyon type environment where satellite masking and multipath are of great concern. On a boat, sky visibility is pretty good, even in the river bottom, and multipath is much less of a problem due to the composition of the surrounding landscape. Additional sensors wouldn’t add much since a boat is fairly low-dynamic vehicle (most GPS receivers can easily do 6g’s or more).
Features I like (sorted by importance):
1. Large Display
2. Buttons big enough to operate with gloved fingers
3. >500 waypoints (yes, you will eventually have more than 99) with the ability to name each. “Mark0035634” might mean something for about 5 minutes after you set it, but you’ll never remember it tomorrow.
4. >25 Routes, reversable
5. “Plot” screen that shows where you are and where you’re heading, and includes the destination waypoint (minum) and all nearby waypoints if possible. It needs to be scalable so that you can hone in on the spot once you’re close.
6. Ability to mark waypoints easily, i.e. 1 or two hits to a key. By the time you navigate through 9 menus, you’ve slid off your spot.
7. Vehicle mount/external power supply. If you do not get this, be sure to check the battery life of the unit and don’t be fooled by “4 fixes per hour” stuff. Find out what it will do with the thing continuously on.
8. External Antenna input – typically you don’t need this, but if you have a tiller-style boat where the electronics are encased and have poor sky-visibility, it could be a life-saver.
9. A PC interface & software that’s compatible. You can click stuff in Delorme Street Atlas and then enter it in by hand, but its time-consuming.
Things I consider “fluff”:
1. Moving maps – these might be useful if you’re in a thick fog on waters where there are islands and obstructions, but for the most part, you know the general layout well enough, and can always use routes to avoid large land-masses. If a company comes out with a unit that will take lake-bottom maps, I may change my mind.
2. “Steering” screen. The Plot screen basically tells you everything that’s on here, and is much easier to use.
3. WAAS – This is actually a different signal that can be tracked and is quite expensive. WAAS was put in place prior to the presidential initiative to turn off the signal corruption that civil users had to deal with prior to May 2000. The accuracy enhancements are less than those of differential (DGPS).
4. DGPS – Prior to May, 2000, this may have been the civil market’s best friend. The coast guard provided a separate radio link that gave corrections to each satellite based on surveyed positions they had set up along navigable waterways. The only remaining errors were those associated with geographic bias (the difference in satellite line-of-sight between you and the transmitter). Ag-Vision and Transit-master systems use differential to meet the strict accuracy requirements laid out by the EPA to keep farm sprayers away from waterways. Sub-meter accuracy is easily achievable using DGPS. The reason I consider it ‘fluff’ is logistical: Once you get close to your spot, you’re going to use the depthfinder to locate exactly where the fish/structures are anyway, so you’re paying extra cash for accuracy you don’t need.
If you’re still thinking about a stationary unit, consider this: If you live in Minnesota, Wisconsin, or Iowa, 1/2 of your fishing hotspots are under the ice 5 months out of the year! The handheld would be much more convenient than pushing the boat across the ice.
This is turning into a book. I gotta go! Best of luck – Gianni
Edited by Gianni on 10/05/01 08:43 PM.
