As a bit of a techy I thought I would whip up a simple program to display max speed, distance etc.

I have the specification of the NMEA sentences that are logged but am intrigued to see that my results differ from Realspeed.
I'm using the maximum speed written to the file (RMC and VTG) and not calculating it.

How are the distances calculated ?

Are there any standards for this sort of software with regards to accuracy ??

Any thoughts ?

Distances is usually calculated from the trackpoints Lat. / Long. It is accumulated and takes into account the non spherical nature of the Earth.
In RealSpeed, I believe Mal has included an algorithm to calculate distances from the doppler speeds and the time. (Meters per second).

It is accurate if it agrees very closely with RealSpeed and GPS-Results.

Hmm this is getting interesting.

What about altitude ? if you're going up and down in ocean swell !

Which is more accurate, GPS calculated speeds (Using altitude and Co-ords) or Realspeed ?

I'm starting to understand why guys like Finian don't value the speeds recorded with GPS's.

Select to expand quote

whippingboy said...

Hmm this is getting interesting.

What about altitude ? if you're going up and down in ocean swell !

Which is more accurate, GPS calculated speeds (Using altitude and Co-ords) or Realspeed ?

I'm starting to understand why guys like Finian don't value the speeds recorded with GPS's.

The software has the ability to disregard altitude in the calculations so it is not a factor.

The GT-11 Speed Genie calculated speeds usually agree to the third decimal knot with those calculated in RealSpeed. However, the RealSpeed analysis is more accurate/reliable as the user is able to filter out spikes and errors automatically as well as manually.

The factors you mention have little to do with Finians so called distrust of the GPS values. It is much more to do with protecting vested and commercial interests. However....
The current recreational GPS are not acceptable for world records by the WSSRC at the moment because the accuracy cannot be 'proved'. 99% of the time it may be perfectly accurate to the .05 knot (especially with Doppler) but it is not possible to provide absolute technical proof of that. Developments continue...............