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I am trying to clean a shapefile to make it usable for routing with pgrouting, postgis, postgresql.

Here an intersection, it seems to be connected but when we zoom …. It is not:

not zoomed 1 zoomed 1

Same here :

not zoomed 2 zoomed 2

Here (it is zoomed at max) there is 2 ways when it seems to be one, and only one is connected :

zoomed at max 2

I am using assign_vertex_id with different tolerances. And QGis and postgis but I don't know what to use in it. Thanks.

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I wonder: are these truly errors? For instance, both situations could be used to represent a two-way street meeting a one-way street. This may be a critical issue, because you don't want to introduce new errors in an effort to eliminate others! –  whuber Aug 1 '11 at 22:05
    
In fact it is just an horribly bad shapefile, I want an extremely simple undirected routing, and what you see is very zoomed. –  hokkos Aug 3 '11 at 8:57

2 Answers 2

up vote 9 down vote accepted

You can use GRASS to do some cleaning. I think you need to break those vectors remove duplicates and then snap them. For that there is the v.clean tool with the options break, rmdupl and snap .

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Within PostGIS, try ST_SnapToGrid to snap vertices to a virtual grid. You need to to some detective work to determine what snapping distance to use. It could be a 0.01 (1 cm), or 1.0, etc.

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