Volvo Ocean Race - Wind Interpolation

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Volvo Ocean Race - Wind Interpolation

Postby mclean » Mon Sep 15, 2014 7:08 am

Hi Omar

It looks like the new VOR game interpolates for position like this:

Wind speed: Bilinear interpolation of the speeds.
Wind direction: Bilinear interpolation of the u- and v- components, then inverse tan to get the angle.

Everything else seems to check out fine so far.
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Re: Volvo Ocean Race - Wind Interpolation

Postby omar » Mon Sep 15, 2014 7:26 pm

Thanks David

This is not how interpolation is implemented in Vrtool I'm affraid.
Using U / V components interpolation is a poor choice for wind speeds,
as is explained in this page:

http://gfesuite.noaa.gov/publications/p ... Paper.html

I used the method described in the page below (in uGrib site):

http://www.grib.us/Forum/tabid/55/forum ... fault.aspx

It seems to me odd to use wind magnitude to interpolate wind speed
while using U/V components to interpolate direction. VRTool interpolates
both speed and direction using TWS/TWD pairs.

how much this difference is significant remains to be checked.

Omar
p.s. Volvo 14 prelude polars basic and pro
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Re: Volvo Ocean Race - Wind Interpolation

Postby mclean » Tue Sep 16, 2014 12:25 am

For wind speed it's definitely better to interpolate the scalars - I think that's what the two references you quote are really saying.

But for the direction it's not so clear - the references don't really say either way. Reading the discussions in the VR forums it seems that interpolating the u/v components for the direction might be more or less an industry standard, but my French is not good so I'm not sure about that.

Just approaching Ushant now the wind direction difference is 9 degrees.
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Re: Volvo Ocean Race - Wind Interpolation

Postby omar » Wed Sep 17, 2014 12:50 pm

9 degrees :roll: that much ?
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Re: Volvo Ocean Race - Wind Interpolation

Postby mclean » Wed Sep 17, 2014 10:22 pm

Yes, Ushant is mid-way between grib points and there was a big wind difference either side, so a worst case location. In the open sea it's much better, and it's fine near the grib points. Maximum I have seen so far is 11 degrees - I doubt if it I would ever exceed that.
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Re: Volvo Ocean Race - Wind Interpolation

Postby Misil208 » Sat Oct 04, 2014 8:21 am

So will VRTool be modified to the same interpolation as VORG? It would be great if it's possible
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Re: Volvo Ocean Race - Wind Interpolation

Postby omar » Sat Oct 04, 2014 4:03 pm

download version 2.30
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Re: Volvo Ocean Race - Wind Interpolation

Postby SWarnberg » Mon Oct 13, 2014 4:56 pm

So, which version of the polar database file from vrtoutoulz.fr is the best to use in weather routing; "classical" or "complete"?
I have still not had any luck with the "complete". Either it will not find any routes at all, or the predicted boat speed is way out. The "classical" seems better.
Any suggestions?
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Re: Volvo Ocean Race - Wind Interpolation

Postby omar » Mon Oct 13, 2014 6:36 pm

SWarnberg wrote:which version of the polar database file from vrtoutoulz:"classical" or "complete"?


Classical
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