Area of Irregular Polygon

[Roger Guay]

Beautiful, Alex. I was working on this idea myself, but your scripts is so much more elegant!

Thanks,

Roger



> On Nov 7, 2015, at 4:43 PM, Alex Tweedly <alex at tweedly.org> wrote:
> 
> Actually, you should shorten the maths - makes it a bit more efficient
> 
> 
> function getArea pPts
>   if line 1 of pPts <> line -1 of pPts then return 0
>   put 0 into tArea
>   put empty into oldL
>   repeat for each line L in pPts
>      if oldL is not empty then
>         --         put item 1 of L - item 1 of oldL into dx
>         --         put item 2 of oldL + (item 2 of L - item 2 of oldL) / 2 into avgY
>         --         put dx * avgY into thisArea
>         --         add thisArea to tArea
>         add (item 1 of L - item 1 of oldL) * ( item 2 of oldL + item 2 of L) / 2 to tArea
>      end if
>      put L into oldL
>   end repeat
>   return abs(tArea)
> 
> end getArea
> 
> -- Alex.
> 
> On 08/11/2015 00:09, Alex Tweedly wrote:
>> Roger,
>> 
>> try this (I've done some minimal testing, so do please check it ...)
>> it assumes the polygon is closed
>> 
>> function getArea pPts
>>   if line 1 of pPts <> line -1 of pPts then return 0
>>   put 0 into tArea
>>   put empty into oldL
>>   repeat for each line L in pPts
>>      if oldL is not empty then
>>         put item 1 of L - item 1 of oldL into dx
>>         put item 2 of oldL + (item 2 of L - item 2 of oldL) / 2 into avgY
>>         put dx * avgY into thisArea
>>         add thisArea to tArea
>>      end if
>>      put L into oldL
>>   end repeat
>>   return abs(tArea)
>> end getArea
>> 
>> NB you could shorten it, but I left each math step separate to make it easier to debug / check
>> 
>> -- Alex.
>> 
>> On 07/11/2015 22:29, Roger Guay wrote:
>>> Thanks very much, Scott. I do have a long points list that I would have to manipulate even before apply this technique. I’m not looking forward to that, but I may have to go this route.
>>> 
>>> Cheers,
>>> 
>>> Roger
>>> 
>>> 
>>>> On Nov 7, 2015, at 12:05 PM, Scott Rossi <scott at tactilemedia.com> wrote:
>>>> 
>>>> It looks like this could translate to LC if you have the point locations
>>>> of your polygon:
>>>> 
>>>> https://www.mathsisfun.com/geometry/area-irregular-polygons.html
>>>> 
>>>> 
>>>> Regards,
>>>> 
>>>> Scott Rossi
>>>> Creative Director
>>>> Tactile Media, UX/UI Design
>>>> 
>>>> 
>>>> 
>>>> 
>>>> On 11/7/15, 2:01 PM, "use-livecode on behalf of Roger Guay"
>>>> <use-livecode-bounces at lists.runrev.com on behalf of irog at mac.com> wrote:
>>>> 
>>>>> Can anyone think of an easy way of getting the area of an Irregular
>>>>> polygon?
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> Roger
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