[postgis-users] flow direction (pointer) indexing

[Steffen Macke]

> I am interested in an indexing scheme that will order line segments and
> polyogn "cells" by a flow network, for the purposes of optimizing
> hydrologic models done uysing postgis.

I've used a simple 'on-the-fly topology' water and wastewater networks 
consisting of lines and nodes in ArcView. The flow direction is simply
defined by the digitizing direction of the line. If the flow direction 
changes, you have to flip the line. Traces through the network look
up nodes and lines connected at the start and end points of a line.
While the performance of this approach is not optimal, it is a very
simple and intuitive way of storing the information. It should also
be quite easy to visualize the flow direction. As PostGIS allows multiple
geometry columns, you can add the start and end points of the lines
as separate columns, which could help to improve the performance (depending
on how many vertices your lines contain).

How do you create/edit your networks? I'm currently trying to implement a
network editor for water/wastewater networks in Java that uses PostGIS
for storage.

Steffen