SeeYou question

[Ted Wagner]

Does anyone have any idea how SeeYou calculates the (ground) velocity at any
given fix in a flight?

I'm examining the take-off segment of one of my log files, and when I
calculate the velocity using the ubiquitous Great Circle algorithm from the
previous fix to the current fix, I get velocities that are *much* higher
than what SeeYou shows in the hover-hints as you trace the mouse along the
route.

Hack hack hack

~ted w/2NO

[Ted Wagner]

A specific example:

In the log file in question, my take-off roll begins at 1:24:15pm, when the
latitude/longitute fixes start to move.

Calculating the instantaneous speed as the distance from the previous fix to
the current fix divided by the time between those two fixes, I have these
speeds:
+15 seconds: 43mph
+20 seconds: 59mph
+25 seconds: 72mph
+30 seconds: 81mph

But loading the same file in SeeYou and looking at the data that pops up
next to the mouse pointer and checking the speeds at the same points:
+15 seconds: 13mph
+20 seconds: 22mph
+25 seconds: 33mph
+30 seconds: 43mph

Those are some rather drastic speed differences. The tow plane was one of
Turf's Pawnees, which in the warmest weather don't have me sitting at 35
knots a full 30 seconds into the take-off roll.

The distance algorithm I'm using is the classic Great Circle:

distance_in_miles = 3956.0775034473 * arccos( SIN(lat1) * SIN(lat2) +
COS(lat1)*COS(lat2) * COS(lng1-lng2) )

Any other hackers out there played with this stuff?

-tw

[Jim Vincent]

>Any other hackers out there played with this stuff?

I recommend you post this directly on the Seeyou website...the help you get
there will be far more focused on your needs.

Jim Vincent
N483SZ

[Andrej Kolar]

Hi Ted,

SeeYou uses a filter, a sort of smoothing algorythm for the groundspeed
velocity calculations. Default value is 20s which means that 20 second.
You can control the smoothing through Tools > Options > Statistics >
Groundspeed filter. Set it to "1s" to have "no filter".

Regards,
Andrej Kolar
--
glider pilots use
http://www.SeeYou.ws

On Thu, 2 Sep 2004 22:10:58 -0700, Ted Wagner
> wrote:

> A specific example:
>
> In the log file in question, my take-off roll begins at 1:24:15pm, when
> the
> latitude/longitute fixes start to move.
>
> Calculating the instantaneous speed as the distance from the previous
> fix to
> the current fix divided by the time between those two fixes, I have these
> speeds:
> +15 seconds: 43mph
> +20 seconds: 59mph
> +25 seconds: 72mph
> +30 seconds: 81mph
>
> But loading the same file in SeeYou and looking at the data that pops up
> next to the mouse pointer and checking the speeds at the same points:
> +15 seconds: 13mph
> +20 seconds: 22mph
> +25 seconds: 33mph
> +30 seconds: 43mph
>
> Those are some rather drastic speed differences. The tow plane was one of
> Turf's Pawnees, which in the warmest weather don't have me sitting at 35
> knots a full 30 seconds into the take-off roll.
>
> The distance algorithm I'm using is the classic Great Circle:
>
> distance_in_miles = 3956.0775034473 * arccos( SIN(lat1) * SIN(lat2) +
> COS(lat1)*COS(lat2) * COS(lng1-lng2) )
>
> Any other hackers out there played with this stuff?
>
> -tw
>
>



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