You can find the documentation here. Also look at ST_SimplifyPreserveTopology, might be better depending on how strict you are with how your data gets modified.<div><br></div><div><a href="http://postgis.org/docs/ST_Simplify.html">http://postgis.org/docs/ST_Simplify.html</a></div>
<div><br></div><div><br><br><div class="gmail_quote">On Tue, Feb 14, 2012 at 3:09 PM, Bistrais, Bob <span dir="ltr"><<a href="mailto:Bob.Bistrais@maine.gov">Bob.Bistrais@maine.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div lang="EN-US" link="blue" vlink="blue">
<div>
<p class="MsoNormal"><font color="navy" face="Arial"><span style="font-size:10.0pt;font-family:Arial;color:navy">Wow! Where are the ST_Simplify and other
functions docuemented- in PostGIS docs or MapServer docs?<u></u><u></u></span></font></p>
<p class="MsoNormal"><font color="navy" face="Arial"><span style="font-size:10.0pt;font-family:Arial;color:navy"><u></u> <u></u></span></font></p>
<div>
<div class="MsoNormal" align="center" style="text-align:center"><font size="3" face="Times New Roman"><span style="font-size:12.0pt">
<hr size="2" width="100%" align="center">
</span></font></div>
<p class="MsoNormal"><b><font face="Tahoma"><span style="font-size:10.0pt;font-family:Tahoma;font-weight:bold">From:</span></font></b><font face="Tahoma"><span style="font-size:10.0pt;font-family:Tahoma"> <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><span style="font-weight:bold">On Behalf Of </span></b><a href="mailto:pcreso@pcreso.com" target="_blank">pcreso@pcreso.com</a><br>
<b><span style="font-weight:bold">Sent:</span></b> Tuesday, February 14, 2012
2:44 PM<br>
<b><span style="font-weight:bold">To:</span></b> PostGIS Users Discussion<br>
<b><span style="font-weight:bold">Subject:</span></b> Re: [postgis-users]
advice for quicker display?</span></font><u></u><u></u></p>
</div>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12.0pt"><u></u> <u></u></span></font></p>
<table border="0" cellspacing="0" cellpadding="0">
<tbody><tr>
<td valign="top" style="padding:0in 0in 0in 0in">
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12.0pt">Also,<br>
<br>
In Postgis you can use the ST_Simplfy() function in mapserver zoom (scale
dependent) layers. So you have one dataset, and as you zoom out you display
features represented by progressively fewer vertices. You don't need every
headland of a global coastline dataset plotted until you until you zoom
in. This can give vastly better performance than a shapefile when zoomed out.<br>
<br>
You can use pre-prepared geometries, so each record has more than one
geometry column, or you can do the point reduction on the fly (in the SQL
command in the mapfile DATA statement), whichever meets your needs.<br>
<br>
The default Postgres configuration is for pretty basic hardware. You might
find & run pgtune, or look at the postgres admin docs to configure it to
more effectively use the available memory, and see how to use tablespaces to
manage data & indexes across filesystems to increase overall disk
throughput. <br>
<br>
So it takes some work, but overall, Postgis provides spatial data management
tools with substantial performance optimisation capabilities. But you need to
use them.<br>
<br>
For plotting an entire unsimplified dataset, the overhead of a database will
always be somewhat slower than a file streaming from disk. Note that on good
hardware with an well optimised database even this difference can be
minimised.<br>
<br>
Cheers,<br>
<br>
Brent Wood<br>
<br>
--- On <b><span style="font-weight:bold">Wed, 2/15/12, Stephen Woodbridge <i><span style="font-style:italic"><<a href="mailto:woodbri@swoodbridge.com" target="_blank">woodbri@swoodbridge.com</a>></span></i></span></b>
wrote:<u></u><u></u></span></font></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><font size="3" face="Times New Roman"><span style="font-size:12.0pt"><br>
From: Stephen Woodbridge <<a href="mailto:woodbri@swoodbridge.com" target="_blank">woodbri@swoodbridge.com</a>><br>
Subject: Re: [postgis-users] advice for quicker display?<br>
To: <a href="mailto:postgis-users@postgis.refractions.net" target="_blank">postgis-users@postgis.refractions.net</a><br>
Date: Wednesday, February 15, 2012, 8:14 AM<u></u><u></u></span></font></p>
<div>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12.0pt">On 2/14/2012 1:57 PM, Bistrais, Bob wrote:<br>
> As some of you already know, I’m a newbie to PostGIS and have just<br>
> barely got a test PostGIS database up and running. So, my latest<br>
> question is in regards to draw times. I created a statewide parcel layer<br>
> from a shapefile. At statewide scale, when the application loads, the<br>
> parcel data draws far slower than the original shapefile did. How can I<br>
> tune this so that draw times are better?<br>
<br>
If you are drawing all the data, it will always be slower than shapefiles.
The trick is to not draw more than is reasonable at a given scale. So the
answer is don't try to draw all the parcels for the whole state. As you zoom
in and need to only draw a subset of the parcels, you will start to get speed
advantages by using the spatial (GIST) indexes in postgis.<br>
<br>
create index mytable_the_geom_gidx on mytable using gist (the_geom);<br>
<br>
-Steve W<br>
_______________________________________________<br>
postgis-users mailing list<br>
<a href="http://mc/compose?to=postgis-users@postgis.refractions.net" target="_blank">postgis-users@postgis.refractions.net</a><br>
<a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><u></u><u></u></span></font></p>
</div>
</td>
</tr>
</tbody></table>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12.0pt"><u></u> <u></u></span></font></p>
</div>
</div>
<br>_______________________________________________<br>
postgis-users mailing list<br>
<a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
<a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
<br></blockquote></div><br><br clear="all"><div><br></div>-- <br>Juan Marín Otero<br>GIS Consultant<br><br>-------Visita mi blog en---------------------<br><a href="http://guachintoneando.blogspot.com">http://guachintoneando.blogspot.com</a><br>
---------------------------------------------------<br>
</div>