[postgis-users] Creating a Flow Diagram

[Sufficool, Stanley]

Comments below


> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net 
> [mailto:postgis-users-bounces at postgis.refractions.net] On 
> Behalf Of Bob Pawley
> Sent: Monday, June 02, 2008 9:30 AM
> To: PostGIS Users Discussion
> Subject: [postgis-users] Creating a Flow Diagram
> 
> 
> Hi Stanley
> 
> I'm still in the primary learning stage with Postgis.
> 
> I would appreciate you critiquing my thoughts.
> 
> With the two tables - entity and entity_relationship - the idea is to 
> establish a parent geometry (perhaps a point known to be 
> within established 
> boundries) and establish the position of  child entities ( in 
> my case, 
> process graphics) in relationship to the parent.

That is correct. The entitity table would contain 2d/3d Polygons of your
diagram entities. Points in this table would not work due to st_centroid
in the would-be trigger function. A slight modification would fix this.

> 
> Furthermore, you seem to indicate that any entity can be both 
> a parent 
> and/or a child to another entity.
> 

Yes, this allows for one to many relations of parent to child (1-->2 &&
1-->3) and for network diagrams

> You also indicate that the placement of the child entity can 
> be established 
> in relation to the relative geometric sizes of the entities.
> 

Yes, examples:
For a parent entity (1) with a child (2) placed to the right of the
parent, you would have entity_relation (1,2,1,0,0)
For a parent entity (1) with a child (2) placed to the top of the
parent, you would have entity_relation (1,2,0,1,0)
For a parent entity (1) with a child (2) placed to the left of the
parent, you would have entity_relation (1,2,-1,0,0)
*If anyone actually produces a 3d diagram using the ratio_z, this would
be a first in my book and would be very interesting to see.

> Have I been somewhat correct so far?
> 
> Bob 
> 
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