NOAA

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NOAA

Postby meteo71 » Fri Nov 23, 2012 9:20 pm

hello,

i am a problem with importation NOAA grid
i haven't the same wind in Vrtool and in virtual regatta

for example, in vrtool the wind is : 5.6N and 164° and in virtual regatta, i have : 5.4n and 164°.
in the next square, i have more diffenence. 7.4noeud in vrtool and 6.5 in regatta !!

what is the problem ? can you explain ? i never have the same speed valors between regatta and vrtools but the angle are always good !

thank you

sorry for my poor english, i'm french !!
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Re: NOAA

Postby omar » Sat Nov 24, 2012 10:28 am

hum. yeah.. seems to differ from normal game wind schedule
Not sure how :roll:
http://www.tecepe.com.br/wiki/index.php?title=NOAAWinds
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Re: NOAA

Postby Berg » Sun Nov 25, 2012 10:07 am

Just newly user and registered.
Really impressive tool.

Angles are always accurate against VR, only speeds have a difference that looks like a rounding discrepancy :

I did a calculation base on row degrib data.
u = -1.25m/s
v = 1.74 m/s

VR gets 4.3 Nds / 144°
VR Tools gets 3.7 Nds / 144°

Using u=-1 m/s and v=2 m/s you get 4.3 Nds like VirtualRegatta !!!!

don't know how to change this (currently using "game windspeed rounded" option in degrip import config....). will test the other options and keep you posted.
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Re: NOAA

Postby Berg » Mon Nov 26, 2012 6:04 pm

regarding wind speed calculations.
from NOAA, you get u and v components of speed in m/s
to get VR values from NOAA, you need to apply the following :
calculate speed in km/h : x=sqrt(u*u + v*v) * 3.6
round it at 1 km/h : y=int(x+0.5)
convert to Nds : z = y / 1.852
round to 0.1 Nds : int(10*z+0.5)/10
compared this with 30-40 various cells and it works ;)

As far as I know, VR is calculating in km/h, then 'y' should be used for calculations and final for display purposes.

Hope Omar could implement in a future release 8-)

Thanks Omar for VRTool
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Re: NOAA

Postby omar » Mon Nov 26, 2012 7:43 pm

Berg, I case of game winds (rounded), U and V components are converted
to wind speed (in km/h) and direction in degrees. The wind speed is rounded
to the nearest integer, and converted to knots.
I don't see where this method differs from the one you describe... :?
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Re: NOAA

Postby Berg » Tue Nov 27, 2012 7:15 am

Omar,
I think the difference comes from when you make the rounding.
It looks like VR make km/h rounding after calculating square root of u and v, if you make it before you do not get the same result. The difference is small (up to 0.2-0.3Nds) but visible.
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Re: NOAA

Postby omar » Tue Nov 27, 2012 4:45 pm

Ok Berg. I found the problem. It was not in the rounding itself,
but there was another bug :mrgreen:

Version 2.09 will correct this soon. Thanks for the help :ugeek:
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Re: NOAA

Postby Berg » Tue Nov 27, 2012 6:05 pm

You are welcome Omar.
Happy to be for some little help.
:)
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