Writing my own GPS speed and acceleration logging!

mike_cjo · 04-30-2007, 05:32 PM

Hi,

Does anyone know of a program that i can run that will log my speed, acceleration and direction to a file in a readable format? It doesnt have to be terribly accurate just a rough idea.

I cant use ODB as my car has a stand alone engine management system that doesnt support it.

I dont want any sort of navigation software!

I have found a few programs that do what i want but they only run on windows CE which isnt much help.

Thanks

Mike

mike_cjo · 05-01-2007, 09:00 AM

It doesnt look like there is much if anything out there that will do what i want so i have decided to write one for myself!

So far i have just got a basic thing displaying the live GPS sentances as they come in.

Next will be to get it to parse the sentences to get the information i want out of it.

bungsai · 05-03-2007, 10:12 AM

good luck, im interested. it owuld be cool if you could incorporate a function that did split timing per specified distance too.

mike_cjo · 05-04-2007, 09:51 AM

A little update for you.

I have now got it accurately logging speed and distance to a text file.
I have also added in a test mode so i can test it from a pre recorded log file.

Next job is calculating the acceleration, this should be pretty simple.

Direction and altitude would be quite cool as well.

Funnilly enough i was thinking about adding a split time and average speed feature to it. I think split time would be best if it knew the long/lat of the start line rather than the circuit length as depending on your line that could vary each lap.

bungsai · 05-05-2007, 12:47 PM

Quote: Originally Posted by mike_cjo

A little update for you.

I have now got it accurately logging speed and distance to a text file.
I have also added in a test mode so i can test it from a pre recorded log file.

Next job is calculating the acceleration, this should be pretty simple.

Direction and altitude would be quite cool as well.

Funnilly enough i was thinking about adding a split time and average speed feature to it. I think split time would be best if it knew the long/lat of the start line rather than the circuit length as depending on your line that could vary each lap.

much better idea than mine

keep it up, cant wait.

pleyraki · 05-07-2007, 06:21 AM

Hi.

Would you please elaborate as to how you calculate distance? The GPS just sends speed every say 1 sec, right? Then what?

Thanks.

Quote: Originally Posted by mike_cjo

A little update for you.

I have now got it accurately logging speed and distance to a text file.
I have also added in a test mode so i can test it from a pre recorded log file.

Next job is calculating the acceleration, this should be pretty simple.

Direction and altitude would be quite cool as well.

Funnilly enough i was thinking about adding a split time and average speed feature to it. I think split time would be best if it knew the long/lat of the start line rather than the circuit length as depending on your line that could vary each lap.

mike_cjo · 05-07-2007, 05:08 PM

Hi,

The gps sends out the latitude and longitude of where it is about once a second in the format of Degrees and metric minutes.

to calculate distance you need to use the ‘Haversine’ formula.
http://www.movable-type.co.uk/scripts/latlong.html

This calculates the distance between two points while taking into account the curvature of the earth so you get an reasonably accurate distance traveled.

To calculate the speed you use Speed = Distance/time

I have found that calculating speed over a 4 second period seems to produce a more accurate result than sampling over shorter time intervals.

Hope that helps

pleyraki · 05-08-2007, 11:23 AM

Quote: Originally Posted by mike_cjo

to calculate distance you need to use the ‘Haversine’ formula.
http://www.movable-type.co.uk/scripts/latlong.html
Hope that helps

Thanks a lot, that is exactly what I was lloking for...

mike_cjo · 05-10-2007, 03:11 AM

I took my car for a little test drive yesterday with the laptop running version 1 of the software and got it to log my journey.

Its working surprisingly well!!

A week saturday i have the first track day of the year so we shall see what it does!

Nerd2 · 05-10-2007, 05:17 AM

Presumiably your program doesn't account for altitude change then?

mike_cjo · 05-10-2007, 06:13 AM

not as of yet, although thats a very simple thing to add.

At the moment its not needed its not like im driving through mountains!! And seeing as castle coombe is a relativly flat circuit with no more than a 20ft height difference between the highest and lowest points. The majority of the circuit is flat with a dip and a climb on the main straight. The only other place i will probably use it in the near future will be at santa pod where there is no altitude change in the slightest.

its one of the many things to add at a later date if i even decide i need it.

ElKeeed · 05-10-2007, 07:13 AM

There are lots of progs to log the raw gps data. Personally I would do that and then work on it afterwards. That way you can always change the exact calculations that you make and apply them in retrospect.

Nerd2 · 05-10-2007, 07:20 AM

Wooo, Castle Coombe near Bristol? Small world ;-)

Yeah would need altitude for normal use probably, have you any thoughs on how you would implement it?

mike_cjo · 05-10-2007, 08:54 AM

Im also recording the raw data but i want something i can look at quickly and compair laptimes. Processing time isnt a problem and im not after a 100% accurate speed just a rough idea to see how i improve and what the car can currently do.

i have found a few interesting pieces of information on converting polar to cartesian co-ords which take altitude into account and i may well look into using this method in version 2 at some point.

Yup, the vary same castle coombe!

mike_cjo · 05-11-2007, 06:32 AM

I was thinking about this a bit more last night.

We know the Haversign or great circle calculation isnt 100% accurate as the earth isnt a perfect sphere.

measuring distance usinf 2 sets of polar co-ords is a lot more accurate.

The thing that dawned on me last night was that really i need to include both methods in my software as altitude is only available with a 4 sat lock where as long and lat can come from a 3 sat lock. So i need to keep the Haversign method as a reserve incase i cant get more than 3 sats to lock onto.

I think this weekend i shall start on version 2 of TurfyGPS!