I have a polyline shapefile representing a road network and a second shapefile containing points. I would like to use PostGIS (presumably PgRouting) to identify sub-networks or service areas radiating from these points.
Essentially, I am hoping to ask the question, "Starting from point X, how far could I walk in any given direction, given a total travel budget of 1 km, following the road network?" The result would be a set of clipped polylines representing the total range of travel possibility, given a 1 km travel budget.
For reference, this GRASS analysis appears to be exactly what I want to do (except I want to do this in PostGIS): http://www.gdf-hannover.de/lit_html/grass60_v1.2_en/node57.html#sec:optalloc
This next example appears to be almost what I want to do, except it seems to answer the question "which nodes could I travel to given a travel budget of X distance?" http://underdark.wordpress.com/2011/02/12/drive-time-isochrones/
The second is not quite the answer I'm looking for, as I want the polylines clipped to my travel distance--I don't care if I make it all the way to a node.