On 10/14/10 12:00 PM, Josi Perez (3T Systems) wrote:
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 .
that's pretty tricky. are the 'end caps' on that expansion
rectangular or circular? if circular is acceptable, you could perhaps
calculate the shortest distance of your point from the path (non trivial
if the path is complex), then if that distance is < your 'expansion',
its 'inside'. probably be a good idea to use an overall bounding box to
reject points that are far away to save a lot of overhead.
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