MoTeC Global Forum

Hi there
I don't understand ?
i use the gps in hill climb
GPS speed and track position do not match, there is a lag
Sometimes the maximum speed is not good either I can check it with an alfano
Can you help me ?
Thanks in advance

Hi Phillippe,

There are many factors that impact this. The speed of the GPS (5hz, 10hz, 20hz etc), the number of satellites detected - which can affect positional accuracy, as well as the speed that the channels are logged at. Also the mounting position of the GPS unit has an impact - for instance on the dashboard, next to the A pillar can drastically change its accuracy with changes in direction.

In regards to logging speed, with a 10hz GPS, you will want to log this data faster than 10hz, usually 20hz is sufficient without being wasteful and collecting excessive redundant data samples. If the speed and positional channels are logged slower than the rate of the GPS, there are data points that are being missed.



Are you able to provide some more information, or a sample log file so we can provide further assistance?

Hi Nathan
Find unclosed my configuration and an example of files
Many thanks
Philippe

Hi Philippe,

First thing I notice is the location of the logging. It appears to be a track with heavy tree coverage.



GPS is a very line of sight device, which is affected by materials over the top of the beacon, cloud cover, tree coverage, the ionsphere and many other factors.

The tree cover is a big hinderance, with the GPS coverage complete dropping out in the tight right hander.

You have 6-7 satellites for much of the course, which is less than ideal. 10 or more are required for any kind of positional accuracy

Going off the baud rate of the serial connection, I will hazard a guess it is a 5hz gps. For reference, at the top detected GPS speed in the log set of 144kph, you are getting a sample, every 8 meters.



If you want more accurate data, I would recommend looking at a faster GPS, particularly when you are racing on narrow tracks. You will find that many High speed GPS units for motorsport use actually include accelerometers or gyros and behave like IMU's to interpolate the data.

Many Thanks Nathan
I understand now
Unfortunately I bought last month this L5 because I thought that the L10 will not work with my old dashboard !
All the Hillclimb are not under the trees
And i have an alfano too to compare
Cheers
Philippe