Notices

GPS Track Data and PTPA

 
Old 03-19-2019, 11:29 AM
  #1  
aryork
Addict
Rennlist Member
Thread Starter
 
aryork's Avatar
 
Join Date: Sep 2016
Location: where it gets hot in summer
Posts: 653
Default GPS Track Data and PTPA

In looking at plots of car position in the Track Precision App (TPA), the data looks "chunky" in turns. I assumed I was getting a low data x-fer rate from my Dual GPS puck. Fixed that to 10 Hz, but am seeing the same chunky lines. Exported TPA data to a .vbo file and it looks the same in Circuit Tools (I added the circles on top of the Circuit Tool output). Copied the data from a .csv data export and pasted that into a web app that plots points, and now I am very confused. See images below. The TPA and Circuit Tools plots look like the data points are far apart, thus chunky. But, when I paste the data points, I see that the chunky straight lines are actually made up of lots of points. See plot on right.

This is confusing. If the GPS data points are real, they should show a nice, physically realistic curve. Here's another zoomed in view of part of the track (I added the yellow lines). You can see a straight line segment made up of 10 points. It must be interpolating between the end points of this segment or something, because the car does not move like this.

I was hoping to be able to accurately see the line I am driving, but this is disappointing.

Anyone have any thoughts? I suppose VBox and AIM tools don't give you chunky results...

aryork is offline  
Old 03-19-2019, 01:05 PM
  #2  
Matt Romanowski
Rennlist Hoonigan
which cost no drachmas
Lifetime Rennlist
Member


Rennlist
Site Sponsor
 
Matt Romanowski's Avatar
 
Join Date: Dec 2001
Location: Manchester, NH
Posts: 9,547
Default

There area couple of things going on. Not all 10 Hz GPS data is the same.

Then their is smoothing that goes in most software that is not always apparent, able to be changed, or displayed (or even matters).

But, what I think you are really seeing is the actual GPS points with no interpolation in between. Say that was a 60 mph corner (constant speed for ease of analysis). 60 MPH is roughly 90 ft/sec. Divide by ten and you're only getting a measurement every 9 feet. Those are the points you are seeing. Many (most?) systems and software then use the accelerometers and other data to fill in the points in between.The better the system, the better they usually do it (there is lots of math in there to do it correctly).

Edit. I said 90 ft/ sec, but meant 53.3 knots
Matt Romanowski is offline  
Old 03-19-2019, 03:02 PM
  #3  
ProCoach
Rennlist Member
Rennlist
Small Business Partner

 
ProCoach's Avatar
 
Join Date: Jun 2008
Location: Durham, NC and Virginia International Raceway
Posts: 12,246
Default

Time to add the officially supported VBOX Sport to fix this. 20 Hz.
__________________
-Peter Krause
www.peterkrause.net
"Combining the Art and Science of Driving Fast!"
Professional, Private Driver Performance Analysis
Authorized Sales and Support for AiM Sports, VBOX Video, MoTeC, AutoSport Labs, RaceVoice LLC, Apex Pro and Cosworth Electronics
ProCoach is offline  
Old 03-19-2019, 03:58 PM
  #4  
aryork
Addict
Rennlist Member
Thread Starter
 
aryork's Avatar
 
Join Date: Sep 2016
Location: where it gets hot in summer
Posts: 653
Default

Originally Posted by Matt Romanowski View Post
There are a couple of things going on. Not all 10 Hz GPS data is the same.

Then their is smoothing that goes in most software that is not always apparent, able to be changed, or displayed (or even matters).

But, what I think you are really seeing is the actual GPS points with no interpolation in between. Say that was a 60 mph corner (constant speed for ease of analysis). 60 MPH is roughly 90 ft/sec. Divide by ten and you're only getting a measurement every 9 feet. Those are the points you are seeing. Many (most?) systems and software then use the accelerometers and other data to fill in the points in between.The better the system, the better they usually do it (there is lots of math in there to do it correctly).

Edit. I said 90 ft/ sec, but meant 53.3 knots
Thanks! I was thinking of doing the mph/distance calcs. That turn is a bit slower than 60 mph, but I'll look and see. I also sent the question and images to Dual tech support. I'll post if they answer!
aryork is offline  
Old 03-19-2019, 04:04 PM
  #5  
aryork
Addict
Rennlist Member
Thread Starter
 
aryork's Avatar
 
Join Date: Sep 2016
Location: where it gets hot in summer
Posts: 653
Default

Originally Posted by ProCoach View Post
Time to add the officially supported VBOX Sport to fix this. 20 Hz.
Hmm - where could I get that?
aryork is offline  
Old 03-19-2019, 04:17 PM
  #6  
Matt Romanowski
Rennlist Hoonigan
which cost no drachmas
Lifetime Rennlist
Member


Rennlist
Site Sponsor
 
Matt Romanowski's Avatar
 
Join Date: Dec 2001
Location: Manchester, NH
Posts: 9,547
Default

Originally Posted by aryork View Post
Thanks! I was thinking of doing the mph/distance calcs. That turn is a bit slower than 60 mph, but I'll look and see. I also sent the question and images to Dual tech support. I'll post if they answer!
MPH to ft/s is 150% in rough terms. 60 mph is 90 ft/s. 100 mph is 150 ft/s. I think it's actually 151.5% or something, but I can't remember that.

It's also 3.129317e-12 parsecs/s.
Matt Romanowski is offline  
Old 03-19-2019, 04:18 PM
  #7  
Matt Romanowski
Rennlist Hoonigan
which cost no drachmas
Lifetime Rennlist
Member


Rennlist
Site Sponsor
 
Matt Romanowski's Avatar
 
Join Date: Dec 2001
Location: Manchester, NH
Posts: 9,547
Default

56740.3 smoots/s
Matt Romanowski is offline  
 


Thread Tools
Search this Thread

Contact Us - About Us - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: