[postgis-users] Creating a Flow Diagram with PostGIS

[Sufficool, Stanley]

Here's my possibly buggy 2 cents:

This stores all geometry as geometry, not x,y attribute values. The
intent is to allow moving entities and have the database handle the
updates to related entities. 

=========================================

create table entity(
	entity_id serial not null primary key, 
	the_geom geometry not null, 
	is_calculated bit not null
);

-- Your Entity to Entity relationships with offset multipliers for 
-- placement relative to the parent entity extents and position which 
-- is also relative to it's parent level entity position
create table entity_relation (
	parent_entity_id int not null, 
	child_entity_id int not null, 
	ratio_x float4 not null, 
	ratio_y float4 not null, 
	ratio_z float4 not null,
	primary key(parent_entity_id,child_entity_id )
);


/*
	I havent done triggers, but this should be a trigger function on
UPDATE of parent geomentry
	
	PURPOSE: placement of child entities in relation to the parent
entity, 
		Watch for Recursion!!  1-->2-->3-->1 
		Step 1: Center child on parent
		Step 2: Offset by er.offset_N of parent extents
		Step 3: Mark child as updated to prevent recursion
*/
update c 
SET c.the_geom = 
select st_translate(
	-- Center the child on parent geometry
	st_translate( 
		c.the_geom, 
		st_x(st_centroid(p.the_geom)) -
st_x(st_centroid(c.the_geom)),  
		st_y(st_centroid(p.the_geom)) -
st_y(st_centroid(c.the_geom)),
		st_z(st_centroid(p.the_geom)) -
st_z(st_centroid(c.the_geom))		
	},
	--Translate to the left, right, top, bottom, front, back of the
parent geometry by the ratio (x,y,x)  stored in entity_relation of the
parent entity width/height 
	( st_xmax(p.the_geom) - st_xmin(p.the_geom) ) * er.ratio_x,
	( st_ymax(p.the_geom) - st_ymin(p.the_geom) ) * er.ratio_y,
	( st_zmax(p.the_geom) - st_zmin(p.the_geom) ) * er.ratio_z
),
is_calculated = 1 
from entity as c
join entity_relation as er 
	on c.entity_id = er.child_entity_id
join entity as p
	on er.parent_entity_id = p.entity_id
WHERE is_calculated=0	--To prevent recursive updates
AND p.entity_id = OLD.entity_id	--Update from the OLD trigger record






-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
Pawley
Sent: Sunday, June 01, 2008 2:17 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Creating a Flow Diagram with PostGIS


Hi Robert

I managed to get the function working - in part.

      UPDATE graphics.process_dgm
        Set the_geom = translate(the_geom, (x1 - st_x(the_geom)), (y1 - 
st_y(the_geom)))
 where graphics.process_dgm.id = '178'
 and graphics.process_dgm.id = '181';

This will move a point from one location to another depending on what I 
insert into the x and y column.

But when I attempt to move the geometry that I want moved I get a
message 
"Argument to X() must be a point".

What am I doing wrong??

Bob




----- Original Message ----- 
From: "Burgholzer,Robert" <rwburgholzer at deq.virginia.gov>
To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
Sent: Friday, May 30, 2008 11:54 AM
Subject: [postgis-users] Creating a Flow Diagram with PostGIS


Bob,
I am taking this online, since it is relevant to PostGIS, and I want to
make 
sure that others review my comments for veracity

Original Question:
> At the moment I am importing dxf files, representing process and 
> devices, into Postgis.
>
> Say I want to make two processes A & B.
>
>  I import the DXF graphic representing A and B into Postgis.
>
> I want B to be the first process and the output of B goes to A which 
> is situated to the right of or below B.
>
> Using ST_Translate I need to know the distance in both x and y from 
> the library to where I want to place the images and plug thos values 
> into the Transform function. Perhaps there is a method of building a 
> function to do this?
>
> Bob
>
>

My response:
You do not want to use transform for the location.  It has nothing to do

with the location, only to the projection, i.e., spatial coordinate
system. 
You DO want translate for location, however.  Transform might be useful
if 
your objects are not imported from a standard library that you generate,
or 
are not in the projection that you  wish to use for your interface.

CASE 1 (Objects are in same projection as your "Workspace"):
In this case, we don't really have to "know" where the starting location
is, 
since we have functions that can derive this.  Also, since our shapes
are in 
the same projection as the workspace, we only need the translate
function. 
For this example, we are storing our components in a table called 
"widget_table", and the geometry column is "the_geom".  Let's assume
that 
your original shape location coordinates are (x0, y0, z0), which can be 
obtained from the geometry column by using the function st_x, st_y, and 
st_z, and you want to move them to be located at (x1,y1,z1).  For this,
the 
following translate call would work:

UPDATE widget_table SET the_geom = translate(the_geom, (x1 - 
st_x(the_geom)), (y1 - st_y(the_geom)), (z1 - st_z(the_geom))) ;

CASE 2 (you are importing user defined shapes, or shapes in disparate 
projections):
In this case you WOULD need transform(), to take them from whatever
their 
source projection is, into whatever their base projection is, as follows

(assuming that the workspace coordinate system is decimal degrees):

UPDATE widget_table SET the_geom = transform(the_geom, 4326);

Then, you would need to relocate them to some other point by using the 
function above.  That function could be encapsulated into its own PG 
function of course, something like relocate(x1,y1,z1) which would hide
all 
of the calls to st_x,y and z.


The catch of course, is that it is essential that we KNOW the projection
of 
our shapes before importing them.  That is actually the real sticky part

here, not the movement of them.

HTH,
r.b.


Quoting Bob Pawley <rjpawley at shaw.ca>:

> Robert
>




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