I recently bought the GPS listed below by Sainsmart. I got it working and logging to an SD card. I'm relatively new to all this and I'm trying to determine how accurate it is. I bought the ublox version based on what I've read about how accurate/sensitive it is.
I found reference to "Dilution of Precision" and I was able to put out an HDOP value that ranged from 70-150. I left it running for 1 hour outside with mostly clear view of sky. According to the linked article, anything above 20 is bad. Also, the measured elevation ranged 100' and it was firmly planted in the same position for the entire time.
My goal for the logger is a high altitude balloon project late this summer. I'm playing with it now to learn and get comfortable with it. I'm also waiting for delivery of an external antenna that may boost the signal. I'll compare results with the antenna and without.
There is an enormous amount of material on line for you to read, and googling "gps accuracy" will get you stated.
The bottom line is that with consumer grade GPS units that are WAAS enabled, under excellent conditions with lots of satellites visible, you can expect your indicated coordinates to be within 2-3 meters of the correct coordinates. At other times, locations and conditions, position errors range from 15-50 meters, to no position fix at all.
I'm waiting for my external antenna next week to do some more experimenting. It does have a small ceramic patch antenna already. The u-blox is supposed to be very accurate based on the datasheet so I'll have to play with it some more and see how it goes.
The description of that GPS receiver was written by a pretty good salesman.
An experiment that I would strongly recommend is to set up the receiver where it has a clear view of the entire sky, and collect position data for 24 hours. Then plot the points to see how your position wanders. Do it both with and without the external antenna, and let us know how it goes!
I've read elsewhere that this is a good GPS chip. In fact, many RC airplanes/copters/quads use this chip for auto-stabilizing flight. It should be quite capable. I'll do as you say once I get my antenna and post the results.
I just came across your post and noted that you mention a HDOP value of "70-100". This sound like very high numbers!
Let me guess... are you using the TinyGPS library to get your HDOP values? If that is the case, note that the HDOP values that this library prints out is turned into "whole" numbers. For instance, an HDOP of 120 in actually represents 1.20. And as you can see from the general GPS documents, an HDOP of 1.20 is actually pretty good.
Hope this helps clarify what you are seeing... I know, it can get a bit confusing
Ublox has all the specs for their GPS devices on their web site (www.u-blox.com). I notice that their NEO line doesn't specify any accuracy for vertical position; you should probably look at a different product line for that (e.g. FastTrax).
Haven't located similar for hand held devices - those would be used on the Gnd, and with Mt Everest at 28000 ft, I suppose 30000 would be a good practical measurement confirmation stopping point for the manufacturers.
You'd also run into limitations due to the extreme cold at that altitude, something in the area of -31F/-35C. Bit nippy!
For example, this Garmin Personal Navigator
Page 45 is the spec sheet.
Does not show an upper limit for altitude
But does warn "temperature range of -15C to +70C may exceed the range of batteries."
-15C/5F would imply an unprotected upper altitude limit of around 15000 feet
"commercial GPS gadgets" - I mean GPS gadgets intended for standard population
Avionics and Military grades are something else..
The Mt. Everest limit is not there as a "practical limit", but to limit bad guys mounting the stuff into their ICBMs.
There is a speed limit too - well below speed of sound, afaik.
Well, the owner of glonass might have the same motivation with the limiting bad guys, though.
As VVP said 2w ago "..After the collapse of the bipolar world, our world has not become safer.."..
Those commercial units have export restrictions. If you're using a USA-made unit that doesn't report export restrictions -- that's designed for a worldwide market -- then you can be assured that it's limited to 18,000m.
Anyway, a good high altitude balloon project means 130.000feet altitude at least.
When not having GPS up there working a star/celestial navigation may help. Also a nice project for arduino. A cheap VGA camera module, few dozens stars stored on an sdcard, an RTC running well when below -55degC, a little bit of math, and that is it..
He wants to track the position of the balloon, not the altitude only. The altitude itself could be measured by help of an ionization chamber (easy to make). The position could be tracked by radar (also a nice project). Or, having a beacon up there, you can triangulate with 3 receivers down on the earth (also a nice project). Sending pings from above and to measure the the timing differences - you need 4 arduinos for that - great
