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<div class="moz-cite-prefix">Hmm, I would still think that, as long
as you have a single line per-boat, this would solve your problem.<br>
Because you can find out how often this single line crosses the
bouy area. The combination of ST_Intersection and ST_Dump would do
that for you.<br>
<br>
Try something like:<br>
--------------------<br>
WITH line AS<br>
(<br>
SELECT <br>
gps.gps_track As boat, ST_MakeLine(gps.the_geom ORDER BY
gps_time) As geom<br>
FROM gps_points As gps <br>
GROUP BY gps.gps_track;<br>
)<br>
,intersections AS<br>
(<br>
SELECT boat, (ST_Dump(ST_Intersection(line.geom,
ST_SetSrid(ST_Makepoint(lon,lat),4326)))).geom<br>
)<br>
SELECT<br>
boat, count(boat) As number_of_passes<br>
FROM intersections<br>
WHERE ST_GeometryType(geom) = 'ST_LineString'<br>
GROUP BY boat<br>
--------------------------------<br>
<br>
if your postgres is below 9.0 the gps.tracks might work different.
See manual.<br>
<br>
Cheers,<br>
Tom<br>
<br>
<br>
On 20-7-2012 9:38, Pedro Doria Meunier wrote:<br>
</div>
<blockquote cite="mid:50090AEB.50808@netmadeira.com" type="cite">
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<div class="moz-cite-prefix">On 07/20/2012 07:38 AM, Tom van
Tilburg wrote:<br>
</div>
<blockquote cite="mid:5008FCF7.9010000@gmail.com" type="cite">
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<div class="moz-cite-prefix">Hi Pedro,<br>
<br>
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.<br>
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.<br>
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.<br>
<br>
Cheers,<br>
Tom<br>
</div>
<br>
</blockquote>
<br>
<font face="monospace">Elegant thinking but that would end up in a
*single* line, as I only have the timestamp and (point)geom to
work with.<br>
Thanks for your input though :)<br>
</font><br>
<pre class="moz-signature" cols="72">--
Pedro Doria Meunier
Telf. +351 291 933 006
GSM +351 915 818 823
Skype: pdoriam</pre>
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