Send Message
Weather | Buy&Sell | Forums |  |
Weather | Buy & Sell | Gallery | Forums | |
OK today I did another geostationary test, swapped from 5hz to 1hz about half way through. The device was on a table in our front yard, not perfect skyview, house and trees not that far away. Satelites varied between 8 and 10, predominately 9
5hz gave a distance gain of 64cm/min
1hz gave a distance gain of 47cm/min
doppler speed graph showed a dead flat 0 line, trackpoint speed graph shows intermitent small spikes.
David, I think the RealSpeed division results are based on 2D Doppler speed. I seem to remember having to make some adjustment to get my downhill skiing speeds back to 3D. I remember discussions between Mal and Tom about how accuracy is significantly improved if you can assume constant altitude and use 2D. Conversations I sometimes struggled to follow entirely, but were something along the lines that it gave virtually another sat position that was absolutely known.
Tom Chalko claimed that Doppler speed accuracy actually improves at windsurfing speeds. He had some highly technical explanation for it that I forget now... ahh, actually, I didn't really understand it anyhow. 
It is always worth revisiting and trying to explain seemingly unexpected results though.
There are a number of papers written by university professor GPS boffins that describe the significant accuracy advantages of using Doppler data for speed measurement. Some go back quite a few years. Nobody is advocating Doppler data for calculating position though, as far as I know.
Not sure where to find SDOP, here's the trackpopint table, from a fairly typical section.
Yoyo's just asked me to check unfiltered doppler in real speed, but I'm not booting into windoze again today, it'll have to wait until next time it's absolutely necessary!
GW-52: This GPS was using 9 sats for over 99% of the test. The Speed display was mostly zero with a display of 0.01 knots every now and then. At the very start there were a few higher readings but after less than 1 minute I did not see any higher than 0.01 knots for the next few minutes. RealSpeed data shows the Doppler speed varying from 0.000 to 0.019 knots with only a very few readings above that. The maximum was 0.039 knots. The total accumulated Doppler distance over about 64 minutes was 6.9km. Note that every speed reading will have a small distance added to the total distance but those distances are very random in direction and don't cover much more than a total of a Metre in any direction. The Trackpoint distance was over 27 KM! The SDOP error was correspondingly small. It was always under 0.019 after the first couple of minutes. GT-31: This GPS was using 8 satellites for most of the test but dropped to 7 a couple of times for a minute or so. The speed display varied a lot more and was between 0.01 and approx 0.20, with figures between 0.06 and 0.12 common for the time I watched it. RealSpeed shows Doppler speed varying between 0.019 and 0.058 for a large % of the time, but with significant data up to 0.078 at times. This surprised me because I expected to see it agree closer with the screen display. The SDOP error was consistently at 0.233 with little variation at all over the hour. The big surprise was that the accumulated Doppler distance was just over 82 KM! This was actually larger than the accumulated trackpoint distance of just over 56 km. The positional graph showed about double the spread in area of the GX-52 wanderings. It is difficult for me to quantify the 'wandering' area of the two GPS as RealSpeed only gives coordinates in Degrees and fractions thereof. But I can open both superimposed and see the scale of difference. I will see if I can do a better measurement in GPS-Results. Thats about all the useful info I can assimilate at the moment. I may well see some more significant things when my head stops hurting from this analysis! 
But, on first look it seems to support the GX-52 being significantly more accurate than the GT-31.More tests and time will tell.
My lightbulb has just lit up and I realised that Doppler distance is used for other catagories. The NM, I hour and 24 hrs all use Doppler accumulated distance.
It is not unusual to see that 1hr tracks are offset on the map during the session but the distance should not be affected. Since I always use at least two GPS, I have seen, many times, one GPS produce offset tracks and the other does not. The average speed from each was always virtually the same and well within the Doppler error margins.
OK figured out what yoyo was on about, if you go to "graph fields" in the speed display. then change from "unfiltered doppler" to "speed" You'll see a very similar graph, very different to either "doppler speed" or "doppler speed 3d".
Any way I certainly do on one of my alphas, on speed and unfiltered doppler the "U" looks more like a "W", whereas with doppler it is a nice "U".
I've no idea what this means?
Today I had the GW52 mounted on my helmet and the GT31 on my upper right arm.
Light wind day, so no speed atained, but I think I've found out something.
The 5hz tracks are still a bit "sawtoothy", but for the first time Real Speed calculated alphas! So I think it must have done some good.
Here's my best alpha from today.
speed genie set to 20kts, it's very apparent by the change to small sawtooths above 20. So the yellow is GW, red is GT31
Here's an alpha from last week, with the GW52 on my upper right arm, before smart logger was working, so it's all 5hz. Just to confuse things the colours are reversed and speeds are higher, but it still looks a bit more ragged to me. I'll check the sattelites and stuff later.
I realised that speed genie was miles too high for alphas so went into settings and found, history max had turned off and font had gone back to small!
Changed speed genie down to 7kts and fixed the font and history things.
When I went back into GPS mode, the distance display had been reset, but the best 5 max and best 5 Ns max were still there.
Not sure when the font and history max changed, could have been when I flattened the battery the other day?
Here's the gpsvisualizer view.
notice some GW52 tracks to the east of GT31 and some to the west. Reminds me of the Cobblers walk I did with the GW52 and the position varied over a short time. Something that my GT11 did not do.
I'm trying to figure out the best way to display the 5 best 10s average, to give Locosys useful advice.
At the moment you get 5 best max speeds, then hitting the scroll button gives you the 5 best 10s average. But to fit all five on the display means very small font.
My personal opinion is we need the best 5 10s average but we don't really need the 5 best max speeds. So if we dispensed with the 5 best max speeds, the best five 10s could scroll through in large/larger font. I think scrolling thru the max speeds as well would take too long.
Any constructive thoughts on this?
Manfred tells me there is a new Beta version of GPS-logit for android that can do live uploads to GPS-SS!
That is very interesting stuff because it means there is potential there to update results for events like the Defi or the Barrum Heads etc as they happen.
Manfred is seeking as much feedback as possible on the performance and accuracy of the app in different Phones. Email your findings to info@gps-speed.com
Does anyone know how to clear the data off a GW52 without downloading it?
I have some corrupt data on mine, and every time I try to download from it my computer restarts. I've tried a few different computers with the same results.
Locosys advised clearing the device, updating the firmware, and then trying again, but I can't see how to clear it.
Dylan.
You can clear all data with the utility. There's a "log clear" button next to the "download" button, and a "top 10 speed clear" button beside it.
And you can clear the display by pressing the "adjust" button during the display, this will bring up a rubbish bin icon, just select yes and hit adjust again.
Hmm. The version of the utility they sent me (V1.1B0519A) doesn't have a Log Clear button.
They sent me an updated version that is supposed to include the header in the SBP file, but I haven't been able to get anything off the device since I switched it to 5Hz.
Dylan.
They sent me a different one to test the header.
The version you have doesn't include any of the normal header info in the SBP file. That's why the firmware version is all jumbled up when you upload it to ka72.
It was annoying when Garmin basically ignored the GPX file standard. When a company ignores their own standard, you have to wonder... I'm a bit surprised the files work at all.
Any news as to when the comercial versions will be released? as my GT11 has just about had the Richard
Or
is it a better option going the "android" mobile phone option?
