Posted on 09/29/2005 9:40:54 AM PDT by Delphinium
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I have it's sister unit, the Magellan Meridian Marine. Same basic deal except the city/street portion is a little lighter, but it includes tons of waterway information. I love that thing.
That is truly cool. I had heard that before, but didn't have the details on how to do it. But it only makes sense considering that the sun at its apex, due south, is local noon.
I use my personal GPS60 to map horse trails and help to preserve them against urban sprawl. There is a a national trail riding association that uses the maps I produce and informs land owners of the importance of keeping the trails open and accessible.
Good info!
Thanks all.
"You are here."
Yes it is. Differential GPS just uses another GPS receiver at a known location (and even if it's not known really accurately, you'll still get good relative positions, relative to the other receiver). The other set has a radio, and so must your GPS set. The other set, since it "knows" where it's at, can determine a correction for the position errors due to such things as propagation through the ionosphere (a major source of "unknown" effects), leaving only the inherent accuracy limitations. In practice you might get down to under a meter. The system I'm sort of working on right now does exactly that. If your application need only work in fairly limited area, you can do two or three times as well as with basic GPS.
As I said before there are other things that can be done. Current, or just previous, generation GPS sets pretty much determine position independently of velocity, and if they report velocity do it by differencing position measurements. However the GPS must compensate for the Doppler of the satellites. The net Doppler is a function of the motion of both the satellites and the GPS set itself. The sets have tracking loops that in effect tune the GPS receiver(s) to the proper Doppler shifted frequency. But those loops are independent of, or at most aided by, the position measurements. In the newer sets the Doppler measurements are used to help determine position, along with the basic GPS ranging algorithms and velocity. Velocity (and position which determines the satellite component of the Doppler) measurements are used to set the receiver center frequencies. It all doesn't quite work exactly that way, but it's better way explain it, unless you want a long tutorial on Kalman filters, and GPS codes and so forth. I had a short course (one day) on all that about a year ago, and even I didn't understand all of it, despite having a good background in Kalman filters and some background in basic GPS.
If you know accurately where that corner is, measure where the GPS set thinks it is, then figure out where the other corners should be, given the "error" in that initial position measurement, (IOW if the GPS set says it's 3 arc seconds north and 5 arc seconds east of the known point when it's setting on that point, then the GPS set will similarly read 3 arc seconds north and 5 arc seconds east of the unknown point when you are actually at it). You need to go there fairly quickly after the initial measurement, because the errors change with time as well as position. If you are on foot that might be a little slow, but if you are mostly motorized, and only need to go a foot when you get near those unknown corners, you'd probably be OK. That's going to be pretty to close where the other corners actually are on the ground. A surveying type system would be better, because it can take advantage of knowing that it's not moving, and thus can average measurement over a fairly long time. You can do that manually too, but it's difficult when you trying to locate a known point on the ground, rather than "asking" where am I now.
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They can be that accurate but I find the error to range from 2 to 5 yards. I know because I have a golfing GPS and if they are consistently off by more than 5 no one would buy one.
They sell tens of thousands.
Yes, but you tend to set and drift.
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
Did you realize this thread is nearly 3 years old?
ThomasThomas recommends the tomtom.
My Garmin C550 that I got just a couple of weeks
ago is super. And you can buy one on eBay for
less than $200 including shipping. What a deal!
Call Google, find out which one they use for Google Maps, then - Buy The Other Brand.
I had found *something* and the owner was coming to my house to pick it up - Google Maps put them a block away. Luckily we were on cell phones with each at that time and we were able to find each other. Though I still had to walk to my street corner and wave my arms in the air.
Finding my car in the parking lot at the airport.
He used a special “GPS-like device” to locate it.
Stuning, isn’t it!
ROFLMAO!!
It is best for really important surveys to have your surveyor use surveys referencing back to the original surveys that platted the Township or Quarter.
In the case of property disputes, the original survey that was accepted by the State to platt the land, is what governs INCLUDING any inaccuracies.
The old original surveys were measured out with metal measuring links called “chains” that had set temperature adjustments.
my pro-2006 scanner is still among the best....My 1975 model Mach one speakers are still pumping out solid base out of the 15 inch woofers. Depends on what it is...
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