[postgis-users] Need help constructing a query

[Tom van Tilburg]

Hi Pedro,

You might try to create lines from the boat tracks (see examples in 
manual for ST_MakeLine)  and circles (st_buffer) from the proximity 
areas around the buoy.
Now do a ST_Intersection(boatline, bouycircle). The result should be a 
set of lines within the bouycircle. Every line stands for one pass along 
the bouy.
I think ST_Intersection might result in a geometry collection of lines 
and points so you would have to make a dump of the result with ST_Dump 
and then select only the lines.

Cheers,
  Tom

On 19-7-2012 20:03, Pedro Doria Meunier wrote:
> Hi,
>
> Need help/pointers on how to best construct the following:
>
> 1 known point in a table. (call it buoy)
>
> another table containing the history (with a geom column) of where a 
> particular object (a boat) has been in time/space
>
> What I need to construct is a query that gives me the count of how 
> many times that boat has gone past that buoy.
> (there *will* be more than 1 rows giving proximity of the object to 
> the buoy -- need to get rid of those ;) -- since the boat is slow 
> moving (2-10 knots))
>
> Btw, both tables' geoms srid=4326.
>
> Any help highly appreciated ;)
>
> TIA,
>
> -- 
> Pedro Doria Meunier
> Telf. +351 291 933 006
> GSM   +351 917 999 236
> Skype: pdoriam
>
>
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