[BNM] Can this convoluted JavaScript function be simplified?

[Alex]

Ok, I get it now. Interesting one!

Hmm...



Premasagar Rose wrote:
> Yes, that's it.
> And I want them to be intelligently reassigned in this way:
>
>     * Latitude beyond the poles continues around the other side:
>           o Adding an extra 10 degrees beyond 90 degrees (which is the
>             north pole) becomes 80 degrees latitude, with longitude
>             switching over to the other side, e.g. [100, 50] => [80, -50]
>     * Longitude gets wrapped around to the other side of the planet. E.g.:
>           o -190 becomes 170
>           o 190 becomes -170
>
>     Hope that makes sense.
>
>     Prem
>
>
>
>
> -------- Original Message  --------
> Subject: Re: [BNM] Can this convoluted JavaScript function be simplified?
> From: Alex <alex at fatdrop.co.uk>
> To: Brighton New Media <bnmlist at brightonnewmedia.org>
> Date: 08/11/2008 15:52
>   
>> So you just want to confine the Lat values to values between -90 and 90 
>> and the Long between -180 and 180?
>>
>>
>>
>> Premasagar Rose wrote:
>>   
>>     
>>> A little challenge for the weekend, perhaps?
>>>
>>> I've written a JavaScript function that gives me the results that I 
>>> need, but in quite a convoluted way. I've spent all my brain cells now 
>>> and can't think how to further simplify it. It'll probably involve more 
>>> use of modulus (%) or something.
>>>
>>> The function takes two numbers, which represent latitude and longitude 
>>> coordinates. The idea is that it will "normalise" any invalid 
>>> coordinates (e.g. further north than the north pole, or further west 
>>> than Alaska), so that they become valid again. It's part of geo plugin 
>>> for jQuery that I'm working on.
>>>
>>> Latitude runs from -90 at the south pole, to 0 at the equator, to 90 at 
>>> the north pole.
>>> Longitude runs from -180 west of Alaska, to 0 in the UK, to 180 east of 
>>> Fiji.
>>> For consistency, I have -180 longitude always represented as 180 (the 
>>> two coordinates are actually the same).
>>>
>>> The results of a simplified version should be absolutely identical. Any 
>>> suggestions on improving it?:
>>>
>>> ===
>>>
>>> function normalizeLatLng(lat, lng){
>>>     lat = lat % 360;
>>>     if (lat > 90 && lat <= 180){
>>>         lat = 180 - lat;
>>>         lng = lng - 180;
>>>     }
>>>     else if (lat > 180 && lat <= 270){
>>>         lat = 180 - lat;
>>>         lng = lng - 180;
>>>     }
>>>     else if (lat > 270 && lat <= 360){
>>>         lat = lat - 360;
>>>     }
>>>     else if (lat < -90 && lat >= -180){
>>>         lat = 0 - (lat + 180);
>>>         lng = lng - 180;
>>>     }
>>>     else if (lat < -180 && lat >= -270){
>>>         lat = 180 - lat;
>>>         lng = lng - 180;
>>>     }
>>>     else if (lat < -270 && lat >= -360){
>>>         lat = lat + 360;
>>>     }
>>>  
>>>     if (lng <= -180 || lng > 180){
>>>         lng = (lng % 180) - (lng > 0 ? 180 : -180);
>>>         if (lng === -180){
>>>             lng = 180;
>>>         }
>>>     }
>>>     return [lat,lng];
>>> }
>>>
>>> ===
>>>
>>>     I look forward to any suggestions.
>>>
>>>     Cheers,
>>>     Premasagar
>>>
>>>   
>>>     
>>>       
>>   
>>     
>
>   

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