[BNM] Can this convoluted JavaScript function be simplified?

[Alex]

Ah yes you're right... I'm guessing it's a bug with > should be >= or 
something, I don't have time to look for it now. It's a good one though. 
My thoughts are that splitting into quarters is a good way to approach it.

Good luck with it anyway, I'm shutting down for the evening...

=]


 

Premasagar Rose wrote:
> Thanks Alex.
> Hmmm - no, that doesn't seem to do it.
> I wrote a little test function to highlight differences between my 
> original function and the new, simplified function. It'll log these in 
> the Firebug console:
>
> ====
>
> var lat, lng, testFunc, normLatLng, testLatLng;
> testFunc = getLatLong;
>
> for (lat=-360; lat<360; lat+=45){
>     for (lng=-360; lng<360; lng+=45){
>         normLatLng = normalizeLatLng(lat,lng);
>         testLatLng = testFunc(lat,lng);
>         if (normLatLng[0] !== testLatLng[0] || normLatLng[1] !== 
> testLatLng[1]){
>             console.log([normLatLng, testLatLng]);
>         }
>     }
> }
>
> ====
>
>
> -------- 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 17:19
>   
>> Bit of a headbender that one!!
>>
>> I *think* this works. haven't tested much.. dunno if it's simpler or not:
>>
>> function findQuarter(coord){
>>   var qtrs = Math.floor(coord/90);
>>   qtrs -= (Math.floor(qtrs/4)*4);
>>   return qtrs;
>> }
>>
>> function findCoord(i) {
>>   if( i > 0 )
>>     i = (i % 90) + (findQuarter(i)*90);
>>   else
>>     i = (90-(i % 90)) + (findQuarter(i)*90);
>>   if( i > 180 ) i = 360 - i;
>>   return i;
>> }
>>
>> function getLatLong(lat, lng) {
>>   lat = findCoord(lat);
>>   lng = findCoord(lng);
>>   if( lng > 90 || lng < -90 ) lat = 0 - lat;
>>   return [lat, lng];
>> }
>>
>>
>>
>> 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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