Which GPS module... 12 or 20?
Wildatheart
Posts: 195
The “GPS Module Comparison” information listing found at http://www.parallax.com/ProductInfo/Accessories/GPSComparisonTable/tabid/831/Default.aspx ·informs us that “source code examples” (and hopefully Basic Stamp circuit connections) can be found on the product page.· A question, probably for the Parallax folks, is… when might this information be available? ·Or is it already?
Then also, it’s stated that some GPS modules track 12 satellites, and some track up to 20.· Assuming 20 tracking’s are better (if a larger number means higher precision), why wouldn’t we spend the additional $10 for the more precise GPS module?· After all, most of us end up very discouraged if our projects end up traveling on the wrong side of the street.
Then also, it’s stated that some GPS modules track 12 satellites, and some track up to 20.· Assuming 20 tracking’s are better (if a larger number means higher precision), why wouldn’t we spend the additional $10 for the more precise GPS module?· After all, most of us end up very discouraged if our projects end up traveling on the wrong side of the street.
Comments
I'll bet they have some code examples up there pretty quickly. Thanks for pointing out the new pages.
Spend the additional $10 for the SiRFIII-compliant modules. I've worked with both of them and the PMB-648 really boots up quickly and receives signal very fast.
Ken Gracey
From your response, and having done some additional reading, it seems that opting for the SiRF STAR-III chipset with its ability to track 20 satellites translates into improved speed rather than improved accuracy from the GPS receiver. For many applications increased speed would be desirable, but at best, the accuracy of the system seems to remain at about 5 – 10 meters. If that’s a realistic anticipated accuracy, is that +/- 2.5 – 5 meters or is that +/- 5 – 10 meters? But either way, the increased processing speed offered by the SiRF STAR-III would help greatly if several readings could be taken and then averaged to achieve greater accuracy. From your experience with GPS, could it be said that averaging multiple readings would equate to better accuracy?
The "base" GPS parallax sells in my opinion shows a significative delay in the reading. I'm using it with the propeller, and is looks like you have the data with some seconds of delay. It is evident if you go with it and check the speed. If you stop the 0 speed will arrive with some seconds delay. I tested also another GPS (sanav) and it looks more responsive, but I had not a chance to use them side by side.
If you use it with basic stamp you must rely on the smart mode, and it is slower by definition.
GPS error is related to external factors, mainly atmospheric, and is not heavily dependent on the model. Averaging multiple reading in a short time is not supposed to help you, because the error source is constant during the averaging. This is solved by DGPS (Differential GPS, you have two units talking, one fixed. External errors are common and are eliminated), but the price tag is sky high. Moreover DGPS have a greater relative accuracy, and better abolute accuracy only as long as your base has precise (known) coordinates.
The error increase also if you see a small number of satellites, and not evenly distributed. This is still a common source of error, but not solvable.
Performance can help you when fixing, taking less time, and keeping the fixing even in adverse conditions (trees and so on), or having lower errors in adverse conditions.
I assume navigators "snap" your car to the right side of the street....
Massimo
Regarding the 12 v. 20 question - the units that track 20 are SiRF chipsets - they lock onto signals more quickly, too. That's the benefit that I like. The specs in signal acquisition don't show much difference and it's my view that the PMB-248 spec should be several minutes instead of 30 seconds (or whatever it is). I don't there's more accuracy with the 20-satellite versions.
Ken Gracey