[mapserver-dev] Call for vote on RFC 78

[Brent Fraser]

Daniel,

   Makes sense.  As Steve W. points out, it could be done on angles by 
averaging the components so you may want to at least keep it in mind for 
a future enhancement when doing the implementation.

   Looking at the FTP site I listed, I see that the U/V components are 
available for wind, but in separate files: nww3.UGRD.grb, nww3.VGRD.grb 
(with 61 bands per file, one band per 3 hr forecast) .  Would it be 
possible to adjust the DATA object to allow for such a situation?  
Something like:

DATA nww3.UGRD.grb:1, nww3.VGRD.grb:1

with the ":1" indicating the band to use.

Best Regards,
Brent Fraser


On 11/16/2011 10:43 PM, 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.
>