[postgis-users] images in postgresql

[Paragon Corporation]

Ben,
 
My understanding is the same (as long as you don't select the column that
is) otherwise has to be detoasted. As I recall, I think a small bit will be
stored and then the rest that doesn't fit into (I can't recall maximum
space), gets chunked into toast records.
 
Its true for most of the databases I've worked with - e.g. large text or
blobs just the pointer is stored in the main table, except PostgreSQL makes
this decision conditionally on size and other databases make it beforehand
based on data type.
 
However -- UPDATES will be painful I think because even though the data is
toasted, PostgreSQL will still create an MVCC copy of the whole record when
doing updates and slushing around big pictures and geometries can be
painful.  So if your other wind turbine info gets changed more often than
the photos, I would keep them separate.
 
 
Leo
http://www.postgis.us
 

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Ben
Madin
Sent: Monday, March 07, 2011 8:31 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] images in postgresql


Robert, 

On 06/03/2011, at 4:28 PM, Robert Buckley wrote:



The windturbine table exists in EPSG:4326. I made a seperate table for the
images because I didn´t wan´t to blow the size of the wind turbine table out
of proportion and jeopardize performance.



My understanding - and if I'm wrong I need to know(!) - is that the sort of
data you are talking about (large geometries or blobs - for your pictures)
are not stored in the primary table, but in associated storage space, known
as TOAST tables. 

This has important implications for indexing, but is brilliant because the
content of these data fields does not directly impact on the number of pages
that the table takes, hence rapid searching is still possible.

cheers

Ben







I am making a simple application to show wind turbines as wms and I wanted
to show the turbine in a popup. I´m not sure how to get the popup to display
though.

Any examples?
Thanks,

Rob




  _____  

Von: Paragon Corporation <lr at pcorp.us>
An: PostGIS Users Discussion <postgis-users at postgis.refractions.net>
Gesendet: Samstag, den 5. März 2011, 18:21:49 Uhr
Betreff: Re: [postgis-users] images in postgresql


Robert,
 
Is there a reason why you have the points in a separate table or do you have
points in both tables and you want to relate by a spatial join?
 
  If its a 1 to 1 relationship, we would just put them in the same table.
 
As far as foreign keys go, you should have some identifier the same in the
two tables.  Do you? 
 
So it would be of the form
 
SELECT wt.wt_id, wt.geom, p.picture
FROM windturbines As wt INNER JOIN pictures As p ON wt.wt_id = p.wt_id
 
or if they are spatially related by space
 
 

SELECT wt.wt_id, wt.geom, p.picture
FROM windturbines As wt INNER JOIN pictures As p ON ST_DWithin(wt.geom,
pt.geom, 10)
 
 
The 10 depends on the spatial reference system or if you are using geography
type then it means 10 meters.  So I'm treating the wind turbine location and
picture location as the same if they are within 10 meters apart.
 
BTW: you might want to read the first chapter of our upcoming book.  It's a
free download and answers this type of question with concrete examples.
http://www.postgis.us/chapter_01
 
Leo
http://www.postgis.us
 
 

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Robert
Buckley
Sent: Saturday, March 05, 2011 5:39 AM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] images in postgresql


Hi,

I am just experimenting at the moment with a project and could do with some
advice.

I have created a database which contains photos of Windturbines.  I also
have a postgis database with the locations (points) of the wind turbines and
would like join the photos to the points via a link table or foreign key.

As you can tell, I haven´t too much experience with postgresql and
relational database design. But i can imagine that the task should not be
too difficult.

I am just a bit unsure how to go about it. The photos are on the linux
server and the creation of the table and the insert of the image was
successfull. But how do i get the  join and how would I display this photo
in a geoext project?

thanks for any tips,

Robert





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