[mapserver-dev] Call for vote on RFC 78

Stephen Woodbridge woodbri at swoodbridge.com
Thu Nov 17 08:49:52 EST 2011


On 11/17/2011 12:43 AM, Daniel Morissette wrote:
> On 11-11-16 11:58 PM, Brent Fraser wrote:
>> Alan,
>>
>> Any plans to allow for raster files containing direction values
>> (http://polar.ncep.noaa.gov/waves_old/products.html#grib, esp Mean Wave
>> Dir) instead of calculating it from components? Note: sample data
>> available at ftp://polar.ncep.noaa.gov/pub/waves, e.g. nww3.WVDIR.grb
>> (wave direction)
>>
>
> Brent,
>
> The approach of using u and v bands allows for resampling, which is
> essential to the approach of rendering vector fields at various scales,
> and I don't think is possible with a raster of direction (angle) values.
>
> i.e. as you zoom in and out, with u and v raster bands, you can average
> the u and v pixel values independently over an area and the average u
> and average v give you an accurate average vector for the area. However,
> I could be wrong, but I don't think you can resample and average the
> direction (angle) values over a block of pixels to get the same result.
>
> It's late here, so maybe you can prove me wrong.
>

It seems to me that if you have the angle the the sin and cos of the 
angle will give you the u and v and you can average them to get the same 
result.

-Steve W


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