DepthmapX remote analysis
Once both map and unlinks layers have been verified, and no problems are reported, the user can use this axial model to run a space syntax analysis using depthmapX. Instead of manually exporting the layers and importing them into depthmapX, the SST offers a “depthmapX remote” tool that takes care of the entire process without leaving QGIS.
Note: DepthmapXnet must be installed and running before starting an analysis (see Additional requisites for details).
The “depthmapX remote” tab controls the analysis in depthmapXnet of the model consisting of the selected map and unlinks layers. The analysis settings in this panel emulate what one would find in depthmapX, but in a more compact layout. One can choose between axial (topological) and segment (angular) analysis. In the first case, the axial map and the unlinks are submitted, analysed and the analysis results returned. In the second case, the axial map and the unlinks are submitted, a segment map is created from these two layers, the segment map is analysed and the results are returned in the form of a segment map.
The radius distance is “n” or “0” by default, meaning a full global analysis without radius restriction. The field accepts a list of comma-separated values for different radii, which are by default topological steps in the case of axial analysis, and metric distance in the case of segment analysis. The topological steps respect the way depthmapX works, where radius 1 corresponds to connectivity, and radius 2 corresponds to the most local analysis, referred to as R3 in most literature.
Additional “Advanced settings” are available via the “Settings” button. Here the user can choose to calculate a full set of graph measures that are not used very often (unchecked by default), and to include choice measures in the analysis (checked by default). In the case of segment analysis, there are additional parameters: the type of radius distance (metric by default) can be metric, angular or topological; and the stubs removal percentage used when converting an axial map into segment map (40% by default).
The “depthmapX remote” tool automatically suggests an output table name for the analysis results, which can be edited by the user. By default, the analysis output name is the same as the axial map layer, and the results are added to the layer in the form of new or updated attributes. If a different name is given in the “Output table” field, a new table is created. The segment analysis results always create a new table, with the suggested “_segment” suffix. The new tables are stored in the current data store location, and the user should confirm that it is the desired location. When a new table is created, the tool checks for an existing table or file with the same name, and if a duplicate name is found it asks the user if she wishes to overwrite it.
Once all the settings are correct, clicking “Calculate” sends the model data and analysis parameters to depthmapXnet for analysis. depthmapXnet must be already running in the background, or a warning is given. A summary of the analysis settings is written in the report window for verification. If there is a problem with the map layer, the analysis stops with an error. If there is a problem with the unlinks layer, a warning is given and the analysis continues without unlinks. In either case the user should run the layer verification steps on both layers. While the analysis is running, both QGIS and depthmapXnet must be kept running throughout, otherwise the connection is broken and the analysis results are lost. The analysis can be cancelled midway through using the “Cancel” button. When the progress bar reaches 100%, the analysis is complete and the report displays the analysis running time.
The post-processing stage takes place on the QGIS side. The results are filtered to include only the standard attributes (i.e. ref, connectivity, choice, integration, node count, total depth, line length) or include the full set. In segment analysis NACH and NAIN are calculated. Finally, the attributes are renamed to be compatible with the selected data store format. Shape files in particular are very restrictive when it comes to attribute names, being limited to 10 alphanumeric characters. Therefore, the names are shortened as much as possible using a predefined conversion table (attribute names conversion) to avoid duplicate unintelligible names (e.g. Choice1, Choice2, Choice3, etc.).
Spatialite and PostGIS tables do not have an attribute name size restriction, but having capital letters, special characters (such as square brackets), or spaces in the names requires the use of double quotes when creating SQL queries, which should be avoided. Therefore, the names are converted to lower case and spaces and special characters are replaced by underscores '_'.
The results layer is added to the layers panel of QGIS. The attributes with the results can be seen in the attributes table of the results layer. However, the best way to explore the analysis results is using the “Attributes Explorer” tool.