Stephan, I have a tool for generating city blocks from street center lines. 1. Given centerlines, street widths and street names (from Google Maps), calculate intersections, blocks and block sides; 2. All geometries are inserted into PostGIS tables; 3. From these table I can generate a virtual city based on building typologies and development histories for any year over a 200 year time interval. 4. Display in Xj3d or Google Earth (COLLADA).
I would like to hear more about your project. Dave van Bakergem -----Original Message----- From: [email protected] on behalf of Stephen Woodbridge Sent: Thu 4/23/2009 2:29 PM To: PostGIS Users Discussion Subject: [postgis-users] How to create block polygons from street network? Hi all, Here is an interesting problem that I could use some suggestions and/or sample code for. I have a street network where all the street segments are noded at intersections. What I need to extract is all the blocks in the coverage. A "block" is the smallest polygon bounded by segments that does not have any segment crossing it. It could have a cul-de-sac protruding into its interior as long as it does not divide the polygon in two. I could create a node adjacency list, but I'm not sure if that helps me. I'm thinking that each edge needs to be tagged with a right and left polygon id, then you can create polygons by grouping on the id. while (current = get_edge_without_rl_pid) { if current.right_side_edge has no pid { get new_pid as this_pid get other edges from end find right most edge if edge has id then { update all new_pid to id mark new_pid as unused this_pid = id } else mark both edges as this_pid } if current.left_side_edge has no pid { get new_pid as this_pid get other edges from end find left most edge if edge has id then { update all new_pid to id mark new_pid as unused this_pid = id } else mark both edges as this_pid } } Does this seem like it would work? Anyone interested in turning this into plpgsql? It might be better to recursively pick an edge and recursively walk connected right most edges back onto itself marking the edges as you go. At some point you may still have edges not included in any of the above that can only be marked by walking the left most edges. Thoughts? -Steve W _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
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