You can select the interval between minimun and maximum timestamp outside each polygon. Interpolate to get a value "when entering" the polygon (intersection between line and polygon) and when leaving.<br><br>Then you can subtract both values to get an estimate of time.<br>
<br>You probably can write a simple function for this.<br><br>George<br><br><div class="gmail_quote">On Tue, Oct 6, 2009 at 11:18 PM, Masanao Yajima <span dir="ltr"><<a href="mailto:yajiyajijp@yahoo.co.jp">yajiyajijp@yahoo.co.jp</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Thank you for your response.<br><br>However, would it be possible to elaborate on the 2nd part?<br>
If my reading of the manual is correct, <br>I believe st_intersection is not implemented to handle the 4th dimension.<br><br>
Masanao Yajima<br><br><div class="gmail_quote"><div><div></div><div class="h5">On Tue, Oct 6, 2009 at 6:47 AM, Suhr, Ralf <span dir="ltr"><<a href="mailto:Ralf.Suhr@itc-halle.de" target="_blank">Ralf.Suhr@itc-halle.de</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div></div><div class="h5">
<div link="blue" vlink="purple" lang="DE">
<div>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);">Hello </span>Masanao Yajima,</p>
<p> </p>
<p>for db-design you can go with ogr2ogr (GPX -> PostGIS). Ogr2ogr
creates point and line geometrys from gpx files. In case of linestring you have
to add the 4. Dimension from the point table.</p>
<p>A optimal query would be the intersection from gps-linestrings
and your polygon area. The result can be many sublinestrings with start and end
time.</p>
<p> </p>
<p>Gr Ralf</p>
<p><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div style="border-style: solid none none; border-color: rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color; border-width: 1pt medium medium; padding: 3pt 0cm 0cm;">
<p><b><span style="font-size: 10pt;">Von:</span></b><span style="font-size: 10pt;">
<a href="mailto:postgis-users-bounces@postgis.refractions.net" target="_blank">postgis-users-bounces@postgis.refractions.net</a>
[mailto:<a href="mailto:postgis-users-bounces@postgis.refractions.net" target="_blank">postgis-users-bounces@postgis.refractions.net</a>] <b>Im Auftrag von </b>Masanao
Yajima<br>
<b>Gesendet:</b> Montag, 5. Oktober 2009 23:03<br>
<b>An:</b> <a href="mailto:postgis-users@postgis.refractions.net" target="_blank">postgis-users@postgis.refractions.net</a><br>
<b>Betreff:</b> [postgis-users] PostGIS to calculate time spent within polygon</span></p>
</div><div><div></div><div>
<p> </p>
<p>Dear PostGIS users<br>
<br>
I am new to PostGIS and I would like expert opinion on how to deal with my
situation.<br>
<br>
I have 2D GPS data and time associated with each points and they represents
line of a trip.<br>
I also have few geographic polygon data representing some area on a map.<br>
<br>
what I want to get out is length of time that is spent within polygon area for
a trip.<br>
<br>
What is the optimal way to design a database and what kind of query would you
use to get such a number.<br>
<br>
One constraint is the time interval for GPS is not accurate so sampling rate
vary alot with in a trip.<br>
<br>
I thought of using time as 4th dimension but I believe st_intersection is not
implemented on the 4th dimension..<br>
<br>
I could do this by bruit force but I am looking for something fast.<br>
<br>
I appreciate your help.<br clear="all">
<br>
-- <br>
Masanao Yajima</p>
</div></div></div>
</div>
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<br></blockquote></div><br><br clear="all"><br>-- <br><font color="#888888">Masanao Yajima<br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>George R. C. Silva<br><br>Desenvolvimento em GIS<br><a href="http://www.sextantegeo2.blogspot.com">www.sextantegeo2.blogspot.com</a><br>