Timing

[Kickstart]

Hi

Just for some people.

You can stick a GPS receiver and PDA under the seat of your bike and record the log of where you have been. This log contains all sorts of info, but from this you can plot an image of the course you have followed. Also you can work out how long it is between you passing the same line multiple times.

I knocked up this (very crude) VB program to decode the logs and plot the course. You can then draw a line on the plot to mark a particular point. It will then tell you how long it is between each time you crossed the line.

There are a couple of different records the GPS unit records. One seems more accurate, the other holds speed as well. The program lets you select which record to use.

It also allows you to select whether to just plot longitude / latitude directly or to convert them to a OS reference (gives a slightly more accurate plot).

This seems to work with the cheap Bluetooth GPS (this one is the one I have used) I have hooked up to a HP iPAQ. Only issue is the exact format they store the longitude / latitude in.

Attached is the .EXE and the source code for people to play with.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Korn]

I played with something similar a while back, using a Garmin Etrex GPS hooked up by serial interface cable to talk to a laptop over NMEA. In the end it wasn't very accurate to use for datalogging, over the course of a few laps the positions would tend to drift quite a bit and with the GPS only updating at 1hz once you got some speed up the datapoints were quite far apart.

Briefly looked at some better receivers which can do 10-25 hz but had a heart attack when I saw the prices. I thought about using several cheap little USB "GPS Mouse" units and averaging between their readings, but never got to try that out.

Cool little track from driving some of the roads around my house:
https://www.kornel.com/gallery/albums/userpics/normal_gps.jpg

2 mile loop of roundabouts and motorway slip roads, with two flyovers at each end which confused the GPS somewhat:
https://www.kornel.com/gallery/albums/GPS/j13.jpg

Straight line down the M3 at speed:
https://www.kornel.com/gallery/albums/GPS/m3.jpg

Two roundabouts at Stockley park, where the big flyover really played havoc with the GPS:
https://www.kornel.com/gallery/albums/GPS/stockley.jpg

Around 20 miles driving up the A316, detour around Sunbury, then up the M3, one junction up the M25 and down the A4 to Heathrow:
https://www.kornel.com/gallery/albums/GPS/a-roads.jpg

Some roads in Central London on a bike, with all the gear in a backpack:
https://www.kornel.com/gallery/albums/GPS/bike.jpg

Driving home from a friend's house a few miles away:
https://www.kornel.com/gallery/albums/GPS/feltham.jpg
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3516 Miles, 11 Countries

[Kickstart]

[G]

Some of the GPSs I've been looking at have 'WAAS' which apparantly makes it more accurate, does yours have that keith?

[Korn]

WAAS is mainly an American system, unfortunately not much good over here as we don't have the extra ground stations that it uses.

The two plots I posted where the drift was noticable were pretty much torture test cases, with lots of roadside trees and time spent under flyovers (one at each end in the case of the longer plot, and a big flyover covering most of the large roundabout in the shorter plot). Reasonable for lap times but the resolution ruled it out for "what line did I take around that corner on that lap" stuff which is what I really wanted to do, so in the end I abandoned it for a simple I/R laptimer.

Do you have a sample datafile I could play with Keith? I don't have anything available in the right format and no VB to fiddle it.
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3516 Miles, 11 Countries

[Kickstart]

Hi

I have one somewhere, might have to grab it from work.

I just wanted a rough plot and more precisely the lap times (oops, did I say lap).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Kickstart]

Hi

Well, disorganised that I am I have found I uploaded it:-

https://www.alfa-pages.co.uk/TempPicture/GPS20050801140124-10255.pgl

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing