Say I have a road network defined by a table, indicating, for each arc, its ID, and its head and tail node. In other words, my network is defined as a directed graph.

For example, we have two points, A and B, linked by a two-way road ; each way is thus represented by a specific arc. It gives us the following table :

Arc_ID | Head_node | To_node
Arc_01 |     A     |   B
Arc_02 |     B     |   A

Each node (A and B) has (X,Y) coordinates, so I drew the network using "LINESTRING" in WKT.

The problem is, Arc_01 and Arc_02 lines are overlapping. I am trying to find a way to draw them so that they do not overlap, and that they are drawn in respect with the way traffic flows on them (right-hand driving).

For that, I thought about calculating the normal vector of each arc, and forcing an offset of a certain number of pixels based on that (so that changing the scale of the map doesn't cause the lines to overlap again), but I have no idea on how to implement it, since I am fairly new to QGIS (I have version 2.0.1 installed) and programming in general.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.