[mapserver-dev] Call for vote on RFC 78

Brent Fraser bfraser at geoanalytic.com
Thu Nov 17 10:21:32 EST 2011


   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.

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