[OpenLayers-Users] Square miles from Square degrees?

[cmose]

Hmmn well the formula seems to match what I turned up online for calculating
the area of an irregular polygon...

The units thing makes sense and since I'm using a degree based map a result
in square degrees also makes sense. What doesn't make sense to me though is
that I manually converted the points in my Polygon to Spherical Mercator
values which should be based on meters so I would expect the getArea result
to be somewhat meaningful as a meters/km but it's still way way too high...

Thanks a bunch for the input!


mpriour wrote:
> 
> Looking at the actual source code, I don't think this method works
> properly on irregular polygons. It also makes the calculations in map
> units. So if you are using feet you get square feet, decimal degrees you
> get square degrees, etc..
> 
> To perform the getArea calculation it does rectangular area measurements
> between the points of the line segments making up the polygon. This works
> in a highly predictive manner with any regular polygon, rectangle, or
> trapezoid. However, it is very unpredictable on free-form geometries.
> 
> 
> cmose wrote:
>> 
>> Hmnn after giving this a go I seem to be getting wildly inaccurate
>> results, at least I believe I am. For instance, I used a polygon over an
>> area I know to be roughly 400k square kilometers. Using the getArea on
>> the polygon (after converting points to sphericalmercator) I'm getting a
>> result of 748,912,714 sq. km...
>> 
>> Anyone have any pointers or ideas of where I might be going wrong here?
>> Thanks!
>> 
>> 
> 
> 

-- 
View this message in context: http://www.nabble.com/Square-miles-from-Square-degrees--tp14357316p14375787.html
Sent from the OpenLayers Users mailing list archive at Nabble.com.