[postgis-users] advice for quicker display?

[Juan Marín Otero]

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>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] *On Behalf Of *
> 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>* wrote:
> ****
>
>
> From: Stephen Woodbridge <woodbri at swoodbridge.com>
> Subject: Re: [postgis-users] advice for quicker display?
> To: 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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>
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-- 
Juan Marín Otero
GIS Consultant

-------Visita mi blog en---------------------
http://guachintoneando.blogspot.com
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