Hi Dylan,
am I right in thinking your system is reading only positional data, ie no doppler and no trapezoidal integration?

If you upload a .sbn file or .sbp file from a GT-31 then the data is doppler. If you upload a file from a GT-11, then the data is doppler except for the Alpha-500 result, which is trackpoints.

.gpx files are treated as trackpoints.

Dylan.

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Te Hau said...

Hi Dylan,
>>>>>>> no trapezoidal integration?

By this do you mean, using 3 measurements for the 2sec result, like realspeed does????

It's the integration method which GPSAR is using now, although on my older version it is an option, not sure if its still optional on updates........has the effect of dropping your speeds ..depressing, that accuracy !

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Te Hau said...

It's the integration method which GPSAR is using now, although on my older version it is an option, not sure if its still optional on updates........has the effect of dropping your speeds ..depressing, that accuracy !

Yep, GPSAR trapezoidal, gives the same results as real speed, before it was slightly greater.

There was a discussion earlier, about how Mal calculated the 2 sec, as the result was always lower than manually averaging the best 2 adjacent results.
Then it was explained that the doppler 1 sec is not the average of 1 sec, it's an instantaneous reading, to get a 1 sec average you need 2 readings, to get 2sec average you need 3 readings, that's why it's less.
I'm sure Dylan has said that his results match realspeed's.

Do you have a link specifying that the doppler is 1sec instantaneous? The Sirf spec sheet suggests that the doppler is the average of 10 x 0.1 sec samples.

(Dylan posting via ka72"s acct)

Yes the KA72 site uses trapezoidal interpolation for speed calcs. 2sec is the most affected. 2sec peak is the average of three seconds data. This is deliberate, and a bit conservative. You can probably get better results from other software by tweaking the settings. KA72 tries to be fair by applying the same rules to everyone.

Dylan

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mathew said...

Do you have a link specifying that the doppler is 1sec instantaneous? The Sirf spec sheet suggests that the doppler is the average of 10 x 0.1 sec samples.

No Mathew, I'm just going by what was posted in a previous thread.
Could there be a difference between the GT11 and GT31, in this, cause I think they have different sirf chips?

If the GTs use the average of 10 X .1sec samples for the 1sec doppler figure then I fail to see why there should be 3 readings involved in a 2sec average???????

(Dylan72 again...)
I've had a bit of a dig this morning, but I can't find anything that would lead me to believe that the GT-11 or GT-31 would use 0.1sec samples. Could you provide a reference?

Unfortunately, the most likely sources seem to be missing or very expensive to access (eg NMEA0183)