#Rcl Simplification
##About This is a plug-in to simplify a road centre line map to a segment map in preparation for angular segment analysis using Depthmap or the Space Syntax Toolkit plug-in in QGIS.
This plug-in was developed by Space Syntax Open Digital Works (C) 2016 Space Syntax Ltd.
The plug-in takes as an input a road centre line map and produces a segment map optimised in terms of angular change and number of nodes in its dual graph representation. The simplification consists of two processes, which are recommended to be made in the following sequence:
- Simplification of angle
- Simplification of intersections
Dependencies: networkx
##Simplification of angle The simplification of angle converts a road centre line map to a segment map that has a simplified dual graph representation with reduced number of nodes and reduced angular change between segments.
The user has to specify the following parameters:
- snap endpoints precision: Avoid disconnections between lines caused by different precisions in the number of decimals of endpoint coordinates.
- minimum segment length: A line is removed if its length is below the minimum segment length parameter.
- minimum angle deviation: Two lines become a straight line if the angle between them is below the minimum angle deviation parameter.
- maximum angle deviation: This parameter is to avoid converting multiple consecutive lines into one when the cumulative angular change is greater than the maximum angle deviation parameter.
##Simplification of intersections The simplification of intersections converts complex intersections into a single node in a primal graph representation and collapses all connected edges to that node.
The user has to specify the following parameters:
- snap endpoints precision: same as above
- intersection distance: Endpoints of multiple lines collapse in a single point (centroid) when the distance between them is less than the specified intersection distance parameter .
- length difference between two segments: The longest line of two lines that share the same endpoints is removed when their length difference is less than the parameter.
- length difference between three segments: The longest line of a triangle of lines is removed when the length difference of it from the sum of the length of the two other lines is less than the parameter.
##Installation Currently the plugin is not available through the QGIS plugins repository. To install you need to download the latest Plugin.zip file from the releases page (link). Unzip and copy the entire folder into the QGIS plugins directory. This directory can be found here:
- MS Windows: C:\Users(your user name).qgis2\python\plugins\
- Mac OSX: Users/(your user name)/.qgis2/python/plugins/
- Linux: home/(your user name)/.qgis2/python/plugins/
This directory is usually hidden and you must make hidden files visible. Under Mac OSX you can open the folder in Finder by selecting 'Go > Go To Folder...' and typing '~/.qgis2/python/plugins/'. If you haven’t installed any QGIS plugins so far, you need to create the ‘plugins’ directory in the ‘.qgis2/python/’ directory. After copying the plugin, it will be available in the plugin manager window once you (re)start QGIS. Check the box next to the plugin to load it.
##Depedencies installation To install networkx install first pip tools. If needed download https://bootstrap.pypa.io/get-pip.py . Open OSGeo4W shell in windows or terminal in mac and go to the directory where the file was saved (type 'cd and the directory path'). Then type 'python get-pip.py' to install pip tools. To install networkx type 'pip install networkx'. To upgrade networkx type 'pip install networkx --upgrade'.
##Notes This plug-in is currently under development. Research and experimentation to define the best graph optimisation processes and to speed up simplification processing time is currently in progress. It has been tested with OSM and OS maps.
##Software Requirements QGIS (2.0 or above)