[postgis-users] Re: flow direction (pointer) indexing

[rajsingh at attbi.com]

The Massachusetts-Rhode Island USGS did something like
this awhile ago. Information is here:
http://ma.water.usgs.gov/streamstats/ and 
http://water.usgs.gov/pubs/wri/wri004135/

I haven´t looked at the project in a few years, but my
understanding is that, as Paul Ransey suggests, they
went the raster route, implementing indexing schemes in 
arcinfo GRID, then in arcview spatial analyst. This was
done to get the processing time down to tens of seconds. 
I have heard that there is a project afoot to replicate 
the project on the national level. This is all 
government work, so I think the code should be 
obtainable if you ask.

- Raj Singh