Math help - rolling average Wind Direction

[wjsmarine]

Hi Folks,

Darrel, am I doing something wrong here with your math example?

When I substitute 350 for Direction and 20 for Sample (a compass difference of 30 resulting in an average of 5) I get:


Direction VAR WORD ; Holds the Averaged wind direction
Sample VAR WORD
AvgCount CON 3 ; Number of samples to average

; Get New Sample here 0-359

If (Direction > 270) AND (Sample < 90) then
Sample = Sample + 360
; so Sample now 380
else
if (Direction < 90) AND (Sample > 270) then
Direction = Direction + 360
endif
endif

Direction = ((Direction * (AvgCount-1) + Sample) / AvgCount) // 360
; becomes
= ((350*(3-1)+380)/3)//360
= ((350*2+380)/3)//360
= (700+380/3)//360
= (1080/3)//360
= 360//360
= 1

; and if swapped so Direction is 20 and Sample is 350
; then Direction now 380
; becomes
= ((380*(3-1)+350)/3)//360
= ((380*2+350)/3)//360
= (760+350/3)//360
= (1110/3)//360
= 370//360
= 1

Or am I missing something obvious..? Math is not my strong point

Cheers,
Bill

[Darrel Taylor]

Missed the Modulas.

360 // 360 = 0

and

370 // 360 = 10

Also, keep in mind it's using a 3 sample running average.
So starting at 350, and a sample of 20, the difference is 30 and it will move 1/3 of that, or 10.
So it ends up at 360(0) after 1 sample.
<br>

[paul borgmeier]

Just curious a bit ... Bill, what are you using to measure this direction 0 - 360?
Thanks

[wjsmarine]

Thanks Darrel, I'll take another look later (time for my beauty sleep).

Paul, it's a 360 degree precision linearity potentiometer fed with a regulated voltage. I use the PIC A2D to derive a count and then process the count for degrees.

Cheers,
Bill

[Darrel Taylor]

Hi,

Just updating this thread with a possible solution to the whole "rolling average Wind Direction" problem...

http://www.picbasic.co.uk/forum/show...6205#post76205

Cheers,