GPS Advice

[Ghost Lemur]

As mentioned above, here you go:

http://www.garmin.com/products/bmwNavigator/

As far as I'm aware it's the only bike-specific product out there, and of course it doesn't do NZ. And, of course, I am deeply humiliated to report that at the moment, Navman doesn't do a motorcycle-oriented product, in spite of the fact that the land navigation division's vice-president rides a V-Rod and an F650, and one of the directors of our American parent company is also on the Harley Davidson board...

So is there at least something in the works in the R&D dept? Obviously you have thrown the suggestion to them that they're missing out on a huge market.

[LB]

Merv: James has one fitted to his F650 - give me an email at work tomorrow and I'll give you his contact details.

[wkid_one]

Isn't half the fun - not knowing where you are going?

[jrandom]

So is there at least something in the works in the R&D dept? Obviously you have thrown the suggestion to them that they're missing out on a huge market.

(a) Whether or not something is in the works is certainly not a matter I'm free to comment on in a public forum! My views expressed here are not those of my employer. Blah, blah, blah. I just happen to like bikes, I don't have any direct influence on Navman's strategic decisionmaking.

(b) Unfortunately the size of the motorcycle market, especially when compared to the cage market, is rather in doubt. And since product development decisions are made on questions of several hundred thousand unit-per-year sales (or not) in Europe and the USA, the response of any potential NZ market would likely be meaningless to any GPS company considering a motorcycle product.

[geoffm]

eTrex Legend + handlebar mount with BrentC's NZ street maps.

You can get all of NZ in the Legends 8mb.

Don't leave home without it.

I use the slightly older map with just streets/roads and it updates in realtime and is excellent for navigation on the fly.

His newer maps have searchable streets as well.

PS. My speedo cable broke about 6 months ago and I just use the GPS.

Where do you get the maps and stuff from? I have an Etrex, which is ok, but doesn;t pick up the satallites very well under trees in the middle of the boonies..
Geoff

[bgd]

http://www.ukgser.com/forums/forumdi...?s=&forumid=46

Lots of good stuff on the above link, although Europe orientated.

[Drunken Monkey]

Well I have the SysOn unit running on my iPaq. WinFast Navigator's velocity field wouldn't display a reading. I have changed the software to Vito Navigator II, which works pretty well.
Now supposedely the accuracy of the GPS speedo is +/- 0.1 km/h. I thought that was a bit ambitious as the position indicator is typically between 5 and 13m out (usually <8m), but I guess if the discrepancy is constant, then it shouldn't matter.
It appears to do a basic d/t calculation, with a short delay between samples (or at least updating the display). This means the feedback isn't 'real time' - there is some lag on the speedo of around a few seconds.
I did a quick test on the way home in the Mitsi = 55km/h on the speedo was giving 51km/h on the GPS, which is about expected. I'll try and get a run past the fixed distance markers at Ramarama before the start of next week and post some more stats. Hopefully the Gixxer will be back soon too and we can see how much that digital dash is out by.

[jrandom]

It appears to do a basic d/t calculation, with a short delay between samples (or at least updating the display). This means the feedback isn't 'real time' - there is some lag on the speedo of around a few seconds.

You got it.

I work with the SiRFStar GPS module (www.sirf.com). It's about the top of current commercial GPS module designs in terms of performance, more or less. It only integrates measurements from satellite signals once per second, so you get a phase delay of about a second in reported position and speed.

And I know for a fact ('coz I've hacked that part of the SiRF GPS firmware) that the reported velocity is a real straightforward one-line 'last time we looked we were over there, how far away and how long ago was it' calculation. You guys should be able to work out pretty quickly what the stated 'accuracy >= 5m' specification does to the margin of error at different speeds.

[k14]

So in other words it is useless for checking the accuracy of your speedo cause it is just, if not more inaccurate than that??

[Drunken Monkey]

So in other words it is useless for checking the accuracy of your speedo cause it is just, if not more inaccurate than that??

Not necessarily = as long as the standard error remains constant, you should be fine. If it was a simple case of the GPS speedo being as inaccurate as the 'standard error', the speedo would be between 18km/h and as high as 47km/h out, which it isn't.

These figures being calculated on:
converting m/s to km/h: m/s * (60sec(in a minute) * 60min(in an hour) = 3600) / 1000m(in a km) = m/s * 3.6

After some more experimenting and research, once you get a 'good fix', the error does indeed remain relatively constant. So it shouldn't matter that the GPS is reporting your distance a few meters from where you actually are, as long as that error stays the same, you are effectively getting an accurate measurement for "d" each time the sample is taken.
It even appears to be measuring my walking speed (of around 5.3 -5.5 km/h) with good accuracy (checked against a stopwatch and a known fixed distance). Yes I had nothing better to do tonight!
Yes it won't accurately read diddly squat if your speed varies, but it doesn't take long to set your speed to a constant and let things settle - especially when you hit that 'cruise control' button.

Besides that, the manufacturer specs indicate a speedo accuracy of +/- 0.1km/h (or about .028 m/s). Surely they wouldn't be fibbing

Between this and my G-timer, I can be a wealth of useless performance statistics about your car/bike/truck/etc...

[jrandom]

once you get a 'good fix', the error does indeed remain relatively constant.

Indeed. In fact, the module manufacturers' quoted 'max errors' are quite conservative. DM's comments re. a 'good fix' are certainly true - with a good view of the sky, accuracy is often sub-metre. It all adds up to GPS receivers providing pretty good speed readings.

It wouldn't be the usual case by any stretch of the imagination for a receiver's reported position to jump around randomly within a 5m radius circle from one second to the next unless it has a minimum of satellites in a bad signal environment.

[jrandom]

Oh yeah, and www.pocketgps.co.uk is a good site for GPS receiver consumer info. They even say nice things about Navman sometimes...