GPS Speed Display

umsam · 04-07-2004, 12:24 AM

I'm working on a project to display speed of a vehicle using GPS data. I ran it on my PII 300Mhz computer, but seems like there's delay representing the data. Can someone in the forum try it out on their faster computer and get back to me with the result. I'll send you the files if you email me. Here's the picture of the display.

cdm · 04-07-2004, 12:31 AM

it's not a computer issue, it's a latency thing. it takes time for data to travel down from the orbiting satellites. it's normal.

umsam · 04-07-2004, 12:40 AM

Thanks, but I know about that issue. When I run it on my PII computer, I can't even move the mouse at real time. When I run it on my desktop, it runs much faster, but I can't move the desktop to test it out. I know the speed won't be totally real time, but I want it to get it close as possible.

siberia37 · 04-07-2004, 08:58 AM

Quote: Originally Posted by umsam

I'm working on a project to display speed of a vehicle using GPS data. I ran it on my PII 300Mhz computer, but seems like there's delay representing the data. Can someone in the forum try it out on their faster computer and get back to me with the result. I'll send you the files if you email me. Here's the picture of the display.

Umm GPS NMEA message come once a second that means your speed will only get updated ONCE A SECOND no matter how fast your computer is. The only way around this might be to use third-party binary protocols offered by Garmin and other GPS's but they will not be compatabile with all GPS's. GPS is just not a good way to get any accurate vehicle speed- OBD-II would be the ideal way to do that.

kiltjim · 04-07-2004, 03:00 PM

I haven't tested it out, but I can see one very big problem right off the bat...

It only goes to 150. Just my 2 cents though. Nice job otherwise.

Scorpnstail · 04-07-2004, 03:31 PM

Quote: Originally Posted by kiltjim

I haven't tested it out, but I can see one very big problem right off the bat...

It only goes to 150. Just my 2 cents though. Nice job otherwise.

where are you driving that you need above 150 ?

Scorp

ukchris · 04-07-2004, 04:13 PM

Have a read through this thread too http://www.mp3car.com/vbulletin/show...6&page=2&pp=15 unfortunately I lost the source code to a disk crash but I may start over when I get my laptop rebuilt. I think the link to Frodo's site has the first version, I have a compiled exe of the second version if anyone wants to try it.

My aim was to display speed, heading etc and then add tracking to this so that the app could run and track where it went and how fast such that you could automatically log data when someone borrows your car etc.

Chris.

ukchris · 04-07-2004, 09:40 PM

My prototype is available here http://www.manwhoring.com/mp3car/ukchris/

Curiosity · 04-07-2004, 10:23 PM

Check your CPU usage. You should really only be using 0% about 95% of the time. If not, either the serial reader is polling instead of waiting on events, or you're drawing more than once per second. Make sure you're not getting hundreds of reads per second on the serial port first. That would really slow things down.

jjh221 · 04-07-2004, 10:40 PM

i like it, 2 cent: colors on most used speeds. like 65 here in states and larger numbers. For me it would be more easy to view the color change than the numbers.

aphesis · 04-08-2004, 06:01 AM

Hi,

I'm from australia and down here we use KM/H would it be possible to change this? By the way i'll email you about testing the program out.

Thanks

gork · 04-16-2004, 01:55 AM

siberia37: actually, binary protocols will not help with the update frequency. Almost all gps's update their position information at 1Hz, and thus their average speed. I looked into GPS's that do it faster and found some 5Hz update models (Garmin GPS16A), but they are all very expensive ($300+) due to this fact. Also, the speed returned by the GPS will be the average speed over the last second (or 1/5 second on a 5Hz gps) immediately when it is sent out the serial port.

You could couple the GPS data with input from an accelerometer to determine speed changes between GPS updates without sacrificing accuracy too much. The math for this dead reckoning gets a little complicated, but it's still very do-able and the accuracy is pretty good, too! www.phidgets.com sells a pretty inexpensive accelerometer.

ob1 · 04-23-2004, 03:33 AM

Quote: Originally Posted by gork

You could couple the GPS data with input from an accelerometer to determine speed changes between GPS updates without sacrificing accuracy too much.

Or you could do some predictive interpolation of just the GPS output i.e. if the last GPS speed read was "v" and the speed before that was "u" and the present moment is "x" milliseconds after "v", the current speed is approximated by:

( (v-u) * x/1000 ) + v

assuming your acceleration rate does not change much over the 1 second interval.

craigyb · 04-23-2004, 03:58 AM

Umsam

Where can we get the code to test it. I will give it a go this weekend.