[GRASS-dev] Script for converting degrees clockwise from North to GRASS convention

[Margherita Di Leo]

Hi Moritz,

thank you for your reply,

On Wed, Jan 23, 2013 at 12:21 PM, Moritz Lennert <
mlennert at club.worldonline.be> wrote:

>
>> If we call WIND the direction map which uses the convention degrees
>> clockwise from North, and GRASS the output map, the rule that I applied
>> is:
>>
>> IF 0 <= WIND < 270     ;     GRASS = 270 - WIND
>> IF WIND = 270            ;      GRASS = 360
>> IF 270 < WIND < 360   ;      GRASS 630 - 0
>> IF WIND = null             ;     GRASS = 0
>> NULL otherwise (this latter I have added to check if there is any error.
>>
>
> This is not correct.
>
> WIND = 0 means North.


Actually this was tricky also for me, but:

Wind direction is measured in:

   -

   degrees clockwise from uphill (direction the wind is pushing the fire)
   -

   degrees clockwise from North (direction the wind is blowing from)

If the wind is blowing FROM north, it means that the arrow is TOWARDS
south.. Am I wrong?


-- 
Margherita DI LEO
Postdoctoral Researcher

European Commission - DG JRC
Institute for Environment and Sustainability (IES). Unit H03 – FRC
Via Fermi, 2749
I-21027 Ispra (VA) - Italy - TP 261

Tel. +39 0332 78 3600
margherita.di-leo at jrc.ec.europa.eu

Disclaimer: The views expressed are purely those of the writer and may not
in any circumstance be regarded as stating an official position of the
European Commission.
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