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Posted by moltilimits on February 21, 2007, 9:15 am


Hi,
please, someone can tell me how can I to calculate the area of a
polygon on the earth's surface where I know the coordinates (lat/lon)
of its points?
Thanks in advance.

Moltilimits


Posted by Sam Wormley on February 21, 2007, 9:30 am


moltilimits@gmail.com wrote:
> Hi,
> please, someone can tell me how can I to calculate the area of a
> polygon on the earth's surface where I know the coordinates (lat/lon)
> of its points?

Since you know the coordinates of every vertex, break it into
triangles. The area of every triangle is that triangle's base
times its height divided by two. Sum the areas.

Posted by Ed on February 21, 2007, 10:52 am


Wouldn't that only apply to a plane? For small areas, it likely
wouldn't matter much, but ...

Arthur Hass

Sam Wormley wrote:
> moltilimits@gmail.com wrote:
>> Hi,
>> please, someone can tell me how can I to calculate the area of a
>> polygon on the earth's surface where I know the coordinates (lat/lon)
>> of its points?
>
> Since you know the coordinates of every vertex, break it into
> triangles. The area of every triangle is that triangle's base
> times its height divided by two. Sum the areas.

Posted by Sam Wormley on February 21, 2007, 11:13 am


Ed wrote:
> Wouldn't that only apply to a plane? For small areas, it likely
> wouldn't matter much, but ...
>

Polygons http://mathworld.wolfram.com/Polygon.html are made up
of planar surfaces.

Posted by Ed on February 21, 2007, 12:25 pm


Well, in "plane geometry," yes. However, the original poster refers to
the "earth's surface." Clearly the earth's surface is not a plane.

I only mean to point out that your suggestion may not arrive at an
acceptable answer for the posters uses.

Sam Wormley wrote:
> Ed wrote:
>> Wouldn't that only apply to a plane? For small areas, it likely
>> wouldn't matter much, but ...
>
> Polygons http://mathworld.wolfram.com/Polygon.html are made up
> of planar surfaces.

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