Today I've updated the ka72.com engine to accept doppler data from within gpx files (if present.)

I don't have a lot of gpx files, but all the tests are good. If anyone wants to try it out feel free.

The results page has stated at the top for a while if doppler or trackpoints was being used for calculations.

The new engine version is 34. (The version used to calculate a file is visible on the "Big List" page.)

Dylan.

Hi Dylan,

Just uploaded 2 files form a Magellan 2minutes ago.
The results now state "Doppler" but all the results are zeroed.

It used to default to Trackpoint.

Regards,

Thanks. Fixed.

I've bumped the engine version to 35, though the fix is trivial.

Dylan.

Hi Dylan,
My GT31 version v1.2, FW B1405x with Mals Real Speed. KA72 points to this old FW
to update but this can no longer happen for some reason. When I post my speeds
to Team Challenge via Ka72 the max speed is always slower than the GPS read out.
eg.25 kn v 28kn. The higher the speed the greater the dif. Is this all happening due to old firmware?
Regards
Mick

Can you point me to one of your recent files on ka72.com?

What location, and date, did you sail.

Dylan.

Michaels.
The GPS readout will always be higher than the 2sec max.
The gps readout is an almost instantaneous measurement.
The 2 sec max is an average of 3 of these readings, this can easily mean a difference of half a knot.

Select to expand quote

Dylan72 said...

Can you point me to one of your recent files on ka72.com?

What location, and date, did you sail.

Dylan.

Thanks Dylan72 and Decrepit.Location is marmong pt. 30-5-10.
mick

Sorry about the delay. Been pretty busy.

I've had a chance to look at this file.

First thing to note is that there are a number of spikes in it. All the software will filter them out, but that is an indicator to me that there may be something sub-optimal with your GPS.

That could be firmware, or it could be that you're wearing it inside your wetsuit. Or it could just be how your GPS works.

Anyway, it's not serious, just mentioning it.

Also, this track shows a top instantaneous speed of 26.106 knots. However, the 2sec peak is only 25.921 knots.

Here is why.

The 25.921 is arrived at by averaging out your best three adjacent speeds, which happen to be:
25.581kt
26.086kt
25.931kt

So, you average 25.581 and 26.086 to get the average speed for that second, and you average 26.086 and 25.931 to get the average speed for the next second, then you average those two results, and you get 25.921.

If you look at where your top speed occurred, the surrounding speeds were not good enough to give you a better 2sec peak, so even though you went faster at that time, you didn't maintain the speed for 2 seconds.

Here are the readings:
23.579
25.289
26.106 (your peak speed)
25.620
25.931

The best 2sec peak around this time comes from the last 3 readings, and is 25.819kt.

That explains why your peak speed is different than your calculated speed.

However, there may be an even greater distance, depending on whether the GPS is telling you the trackpoints speed or the doppler speed. Your peak trackpoints speed in this track is 28.638kt, which is much higher than the 2sec speed. However, that speed has not been adjusted for doppler.

Dylan.

Excellent explanation Dylan, and great to see the actual numbers illistrated.
Interesting that the max display speed isn't part of the 2s result.
Wonder how often that happens.