GPS Update Speed

pmw
Posts: 4
Joined: Sun Feb 12, 2006 9:07 am

GPS Update Speed

Postby pmw » Wed Apr 23, 2008 12:56 pm

Can I ask what rate the GPS coordinates are updated (not sampled). I know the GPS is sampled at 100Htz, but most navigation systems only actually update the GPS coords at 1Htz, with some "high accuracy ones" at 5Htz.

Support

Postby Support » Wed Apr 23, 2008 2:15 pm

Hi PMW,

This has changed over time... and depends on the version of the DL1 that you have.

The original DL1 was 5Hz (orange connector)
The revised DL1 was updated to 10Hz (green connector and early Black connector). Actually strictly speaking the actual rate was between about 8Hz and 10Hz depending in conditions.

The very latest black connector type that we've been shipping for a few months are "dual mode" and can use the advanced RAW GPS processing mode in the analysis software. In normal mode they run at 5Hz, but using the advanced mode they can run at 20Hz. The advanced mode does require and extra licensing code at a cost of about £150.

The actual accuracy of the 5Hz and 10Hz solution is very very similar... in most cases you wouldn't see a difference. The 20Hz solution is much better.

The 20Hz option is very new and there will be more information and example data added to the web site soon about this.

In all cases the GPS and the accelerometer information is combined to give an actual update rate on position and speed of 100Hz in the software.

Kind regards,

Andy
Last edited by Support on Fri Apr 25, 2008 9:18 am, edited 1 time in total.

Turby
Posts: 301
Joined: Thu Nov 17, 2005 2:28 pm

Postby Turby » Wed Apr 23, 2008 4:47 pm

I'm sure the early DL1's had a green connector and the Mk2's had orange...

faraday
Posts: 284
Joined: Sun Feb 25, 2007 1:18 am

Postby faraday » Thu Apr 24, 2008 2:39 am

I've done a lot of real world testing with old, new and in between DL1s and can reiterate Andy's statements. There is many a fine tune played on an old fiddle, so do not despair if you think that your early unit is superceded.
However, the latest customers are getting a bonus they didn't reckon on with the capacity to upgrade to the raw post-processing. At GBP 80 it's well worth it, as racing line analysis is now made possible more often.
The most important point has yet to be made, however, and it is that GPS accuracy will vary with time and location.
It is rare that these local conditions degrade the DL1 performance below that of a conventional wheelspeed/accelerometer logger. Andy's software, however, with its scientific honesty, critically reveals what GPS doubters might refer to as innaccuracy. When we can plot the trajectory of our cars from start to end of run, small deviations are revealed "warts and all".
If conventional loggers attempted this, many users would demand their money back! :cry:

I've 'backed-to-back' tested DL1s with other equipment in very dynamic vehicles. You would have to go to F1 or other elite open-wheelers to find a more demanding application. The early "5Hz" is not visibly less accurate or useful than any later units, until the new "raw" post-processing is considered. This is not because it has a GPS hardware defficiency, but because the processing power of the PC can apply more complex algorithms to compute the vehicle path.
Superior GPS hardware is available (Speedbox), which has "on-board" or "real-time" computational grunt to deliver more accuracy "out of the box". The update frequency is a minor part of the accuracy improvement possible, but it comes at a serious cost penalty.
Value for money, a DL1 can't be beaten, unless you consider the AX22, with its display, of greater utility than a plentiful supply of external inputs.

It may have been argued elsewhere, that other brands of GPS logger that come with display/dash are better value for money. R-T have addressed that with the DL1/Dash2 package deal, but the falling $US may affect some potential purchases. My assesment is that the flexibility of the R-T software makes it better value. For accuracy, the 100 Hz accelerometer processing is necessary. Some rival units do not have this. For those that do, accuracy will depend more on the local conditions than on the choice of hardware, but the R-T software makes it easy to grapically see what the accuracy difference from alternative processing yeilds.
:D


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