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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>OK, I am trying to use the ST_simplify
command but I’m not doing it right. I am using a layer called parcels,
it has columns gid and the_geom, this is the DATA line from my MapServer map
file:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> DATA "the_geom from (ST_Simplify(the_geom,
10.0)) USING SRID=26919 USING Unique gid"<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>What am I doing wrong here?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
postgis-users-bounces@postgis.refractions.net
[mailto:postgis-users-bounces@postgis.refractions.net] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Juan Marín Otero<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, February 14, 2012
3:13 PM<br>
<b><span style='font-weight:bold'>To:</span></b> <st1:PersonName w:st="on">PostGIS
Users Discussion</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [postgis-users]
advice for quicker display?</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>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.<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><a href="http://postgis.org/docs/ST_Simplify.html">http://postgis.org/docs/ST_Simplify.html</a><o:p></o:p></span></font></p>
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face="Times New Roman"><span style='font-size:12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>On Tue, Feb 14, 2012 at 3:09 PM, Bistrais, Bob <<a
href="mailto:Bob.Bistrais@maine.gov">Bob.Bistrais@maine.gov</a>> wrote:<o:p></o:p></span></font></p>
<div link=blue vlink=blue>
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<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=2 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?</span></font><o:p></o:p></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'> </span></font><o:p></o:p></p>
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<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><font
size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;font-weight:
bold'>From:</span></font></b><font size=2 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> <st1:PersonName w:st="on">PostGIS
Users Discussion</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [postgis-users]
advice for quicker display?</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
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<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><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:<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;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<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><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>
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_______________________________________________<br>
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<br clear=all>
<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>-- <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>
---------------------------------------------------<o:p></o:p></span></font></p>
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