Point inside/outside area constructed by an expanded path

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От Josi Perez (3T Systems)
Тема Point inside/outside area constructed by an expanded path
Дата
Msg-id AANLkTim6gLxH5G37N+==6Lija4DnNYmb-d6FWED9-R7s@mail.gmail.com
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Ответы Re: Point inside/outside area constructed by an expanded path  (John R Pierce <pierce@hogranch.com>)
Re: Point inside/outside area constructed by an expanded path  (Merlin Moncure <mmoncure@gmail.com>)
Список pgsql-general
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Hi,

I use postgreSQL.8.4.2 and don't have postGIS installed.
I have a geometric type polygon and I know that it is possible to determine if a point it is inside or not of this polygon, using anything like that:
select polygon('(-23.5672,-46.6510),(-23.5670,-46.65095),(-23.5672,-46.6508),(-23.5672,-46.6510)') @> point('-23.567534,-46.64942')

The question:
Anyone knows an algorithm or have ideas how to determine if a point it is inside an area constructed by geometric type path expanded for a known distance?
Graphically:

the path
            x=========x=======x
 
the path expanded by a distance

            |         | A     |
            |         |       |
     -------x=========x=======x-------  C
            |         |       |
        B   |         |       |

the points A and B are inside and the point C are outside .

Suggestions are welcome.
Thanks in advance,
Josi Perez
 


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