details on converting the wind bearing

[daj]

Can someone point me to a site to convert the windbearing (in degrees) to compass references?

I want to change my wind bearing in the 'dayfile' to compass references for easier reading on the website. I've put it all in a grid for users to scroll through, etc.

I've had a 'google' but I just can't get to a site that will help me!

thanks

[steve]

This is how Cumulus does it. It's Delphi (Pascal) but hopefully self-explanatory

Basically, it's dividing by 22.5 and using that to index the array, but the complication is a shift of 11.25 degrees to get the centre of the compass point. It multiplies by 100 so it can do all the arithmetic as integers.

Code: Select all

function BearingToCP(bearing: integer): string;
// Converts bearing in degrees to compass point
var
  compassp: array[0..15] of string = ('N', 'NNE', 'NE', 'ENE', 'E',
    'ESE', 'SE', 'SSE', 'S', 'SSW', 'SW', 'WSW', 'W', 'WNW', 'NW', 'NNW');  
begin
  Result := compassp[(((bearing * 100) + 1125) mod 36000) div 2250];
end;

[skyewright]

In addition to steve's code, Wikipedia's Boxing the compass page outlines an algorithm for converting degrees to a compass point.

[steve]

Yes, I guess that's a more intuitive way of doing it - it's basically the same algorithm (if you substitute 16 for their 32) but doing the division first instead of last.

[daj]

This is how Cumulus does it. It's Delphi (Pascal) but hopefully self-explanatory

Perfect, thanks

[beteljuice]

Here's some of the JavaScript reasoning that beteljuice uses (ie. 'in the web page')

Code: Select all

......


var langWindDir = new Array( /* used for alt and title tags on wind dir arrow and wind direction display */
	"N", "NNE", "NE", "ENE", 
	"E", "ESE", "SE", "SSE", 
	"S", "SSW", "SW", "WSW", 
	"W", "WNW", "NW", "NNW");

var langWindVerbose = new Array( /* can be used in text for wind direction */
	"North", "North-Northeast", "Northeast", "East-Northeast", 
	"East", "East-Southeast", "Southeast", "South-Southeast", 
	"South", "South-Southwest", "Southwest", "West-Southwest", 
	"West", "West-Northwest", "Northwest", "North-Northwest");






function windDirLang ($winddir) // user language NNW
// Take wind direction value, return the
// text label based upon 16 point compass -- function by beeker425
//  see http://www.weather-watch.com/smf/index.php/topic,20097.0.html
{
   return langWindDir[Math.floor(((parseInt($winddir) + 11) / 22.5) % 16 )];
}	// END function windDirLang


function windDirVerbose ($winddir) // user language North-Northwest
// Take wind direction value, return the VERBOSE
// text label based upon 16 point compass -- function by beeker425
{
   return langWindVerbose[Math.floor(((parseInt($winddir) + 11) / 22.5) % 16 )];
}	// END function windDirVerbose


...

So the html call would be along the lines of:

Code: Select all

<script>
document.write(windDirLang(degrees) );
</script>

[steve]

In addition to steve's code, Wikipedia's Boxing the compass page outlines an algorithm for converting degrees to a compass point.

Actually, there's a bug in that algorithm. Try it for 359 degrees.

[skyewright]

In addition to steve's code, Wikipedia's Boxing the compass page outlines an algorithm for converting degrees to a compass point.

Actually, there's a bug in that algorithm. Try it for 359 degrees.

I presume they just forgot to mention that because the whole thing "wraps around", 32 should be considered the same as 0 in this case?

Here's my 16-point compass C++ implementation of the algorithm. The '% 16' bit handles the case you mention.

Code: Select all

int cardinalDirectionNumber( static_cast<int>( ( ( currentGustDirection / 360.0 ) * 16 ) + 0.5 )  % 16 );
const char* const cardinalDirectionTexts[] = { "N", "NNE", "NE", "ENE", "E", "ESE", "SE", "SSE", "S", "SSW", "SW", "WSW", "SW", "WNW", "NW", "NNW" };
string dirString = cardinalDirectionTexts[ cardinalDirectionNumber ];