[postgis-users] advice for quicker display?

[Stephen Woodbridge]

DATA "the_geom from (select ST_Simplify(the_geom, 10.0) as the_geom from 
mytable) as foo USING SRID=26919 USING Unique gid"


On 2/15/2012 11:03 AM, Bistrais, Bob wrote:
> 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:
>
>    DATA "the_geom from (ST_Simplify(the_geom, 10.0)) USING SRID=26919
> USING Unique gid"
>
> What am I doing wrong here?
>
> *From: * postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] *On Behalf Of
> *Juan Marín Otero
> *Sent:* Tuesday, February 14, 2012 3:13 PM
> *To:* PostGIS Users Discussion
> *Subject:* Re: [postgis-users] advice for quicker display?
>
> 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.
>
> http://postgis.org/docs/ST_Simplify.html
>
> On Tue, Feb 14, 2012 at 3:09 PM, Bistrais, Bob <Bob.Bistrais at maine.gov
> <mailto:Bob.Bistrais at maine.gov>> wrote:
>
> Wow! Where are the ST_Simplify and other functions docuemented- in
> PostGIS docs or MapServer docs?
>
> *From: * postgis-users-bounces at postgis.refractions.net
> <mailto:postgis-users-bounces at postgis.refractions.net>
> [mailto:postgis-users-bounces at postgis.refractions.net
> <mailto:postgis-users-bounces at postgis.refractions.net>] *On Behalf Of
> *pcreso at pcreso.com <mailto:pcreso at pcreso.com>
> *Sent:* Tuesday, February 14, 2012 2:44 PM
> *To:* PostGIS Users Discussion
> *Subject:* Re: [postgis-users] advice for quicker display?
>
> Also,
>
> 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.
>
> 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.
>
> 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.
>
> So it takes some work, but overall, Postgis provides spatial data
> management tools with substantial performance optimisation capabilities.
> But you need to use them.
>
> 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.
>
> Cheers,
>
> Brent Wood
>
> --- On *Wed, 2/15/12, Stephen Woodbridge /<woodbri at swoodbridge.com
> <mailto:woodbri at swoodbridge.com>>/* wrote:
>
>
> From: Stephen Woodbridge <woodbri at swoodbridge.com
> <mailto:woodbri at swoodbridge.com>>
> Subject: Re: [postgis-users] advice for quicker display?
> To: postgis-users at postgis.refractions.net
> <mailto:postgis-users at postgis.refractions.net>
> Date: Wednesday, February 15, 2012, 8:14 AM
>
> On 2/14/2012 1:57 PM, Bistrais, Bob wrote:
>>  As some of you already know, I’m a newbie to PostGIS and have just
>>  barely got a test PostGIS database up and running. So, my latest
>>  question is in regards to draw times. I created a statewide parcel layer
>>  from a shapefile. At statewide scale, when the application loads, the
>>  parcel data draws far slower than the original shapefile did. How can I
>>  tune this so that draw times are better?
>
> 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.
>
> create index mytable_the_geom_gidx on mytable using gist (the_geom);
>
> -Steve W
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>
> --
> Juan Marín Otero
> GIS Consultant
>
> -------Visita mi blog en---------------------
> http://guachintoneando.blogspot.com
> ---------------------------------------------------
>
>
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