User Guide QGIS BETA

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NetworkGT Toolbox
Version 0.1
Björn Nyberg1*, Casey W. Nixon1, David J. Sanderson2
Department of Earth Sciences, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway.1
Faculty of Engineering and the Environment, University of Southampton, Southampton
SO17 1BJ, UK2
*Corresponding Author: bjorn.nyberg@uib.no

Contents
1.0

Background.................................................................................................................................. 2

1.1 Citation and Acknowledgments .................................................................................................... 2
1.2 License ........................................................................................................................................... 2
2.0

Installation ................................................................................................................................... 3

2.1

NetworkGT Download ............................................................................................................. 3

2.2

Python Installation .................................................................................................................. 3

2.3

NetworkGT Toolbox Installation.............................................................................................. 3

3.0

Workflow ..................................................................................................................................... 4

3.1

Digitizing Fracture Network..................................................................................................... 4

3.2

Geometrical Analysis ............................................................................................................... 4

3.3

Topological Analysis ................................................................................................................ 6

3.4

Spatial Analyses ....................................................................................................................... 7

4.0

Contact Information & Feedback ................................................................................................ 8

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1.0 Background
1.1 Citation and Acknowledgments
The NetworkGT (Network Geometry and Typology) Toolbox is a set of tools designed for the
geometric and topological analysis of fracture networks in QGIS 3.4 >. This is a pre-release beta
version that is currently under construction. The toolbox provides a range of tools that allow the user
to utilize a number of traditional sampling methods in order to automatically conduct a robust
characterization of the networks geometric and topological properties as well as assessing its spatial
variability. The toolbox has been designed and made publically available by the authors of this
workflow, all of whom are academic geoscientists. The different types of analyses are described and
discussed in detail within the corresponding article by Nyberg et al., 2018 published in Geosphere. If
you use this toolbox for your own analyses or research we require that any corresponding results,
reports, publications or presentations to CITE AND ACKNOWLEDGE both:
a) The NetworkGT Toolbox
b) Nyberg, B., Nixon, C.W., Sanderson, D.J., 2018, NetworkGT: A GIS tool for geometric and
topological analyses of two-dimensional fracture networks. Geosphere, v. 14, no. 4, p.1-17,
doi:10.1130/GES01595.1.

1.2 License
The scripts used in this program are written in the Python programming language under
a GNU General Public License V3 which states:
“This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see .”

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2.0 Installation
2.1 NetworkGT Download
Download the latest release of the NetworkGT toolbox
https://github.com/BjornNyberg/NetworkGT/releases

2.2 QGIS Installation
QGIS is an open source GIS software that is available Linux, OSX and Windows from
https://www.qgis.org/en/site/forusers/download.html. Download the OSGeo4W
Network Installer (64bit) and follow the instructions.

2.3 Python Installation
2.3.1 Python module installation
The toolset utilizes a set of scientific third-party modules that are typically not available
in a standard QGIS installation. To install these modules requires admin rights and the
following procedure:
1. Navigate to the python 3.X folder that contains a python.exe file of your QGIS
installation. On windows this is located in
‘C:\OSGeo4W64\apps\Python37’
2. Double click the python.exe
3. Type import subprocess and hit enter
4. Type import sys and hit enter
5. Type subprocess.call([sys.executable,’-m’,’pip’,’install’,’pandas’]) and hit enter
Python modules have now been installed!

2.4 NetworkGT Toolbox Installation
1.
2.
3.
4.
5.

Unzip the NetworkGT-version.zip file into a working directory
Open QGIS
Find the Toolbox by navigating to the tabs Processing  Toolbox
Click on the Scripts icon  Add Script to Toolbox…
Navigate to the NetworkGT/QGIS/Scripts folder, select all and open the files

The toolbox is now ready for use under the Scripts -> NetworkGT tab!

Tip - Install the Data Plotly plugin for interactive visualization of your fracture
network attributes!
1. Navigate to Plugins -> Manage and Install Plugins…
2. Search for Data Plotly
3. Press Install Plugin

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3.0 Workflow (Under Construction)
3.1 Digitizing Fracture Network
3.1.1

Interpretation of Fracture Network
The fracture network needs to be digitized correctly as polylines at the
interpretation stage.
It is important to always use the ‘snap’ function when creating fracture
polylines.
This should be used to snap to another fracture polyline if the two fractures
are intersecting or to the interpretation boundary polygon if the fracture
leaves the interpreted region.

3.2 Geometrical Analysis
3.2.1

Fracture Sets
The ‘Define Sets’ tool will define sets by orientation.
This uses the fracture network polyline feature class as the input.
Note that set orientations ranges must between 0-180 degrees and defined
within brackets, with each set separated by a comma – (0,90), (90,180)
Set definitions by bin size will define sets into a series of equal bin size
increments – e.g. bin size 10 = (0,10),(10,20),(20,30)…
The orientations and set numbers will be added automatically to the fracture
network attribute table, allowing the user to then visualize the fracture
network based on these.

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Plot the orientations using the interactive DataPlotly package using the Plot
Type ‘Polar Plot’ or ‘Scatter Plot’ – Select ‘Length’ for the X Field and ‘Orient’
for the Y Field.

3.2.2

Fracture-Size Distributions
 Using the fracture network polyline feature class as an input, distributions of
fracture lengths, displacements or apertures etc can be analysed using the
‘Distribution Analysis’ tool.
 These generate a series of fields in the attribute fields including Cumulative
Frequency (Cum_Freq), Weighted Length Field (LEN), normalized standard
deviation (NSD), log normal standard deviation (LNSD). Display the data using
the DataPlotly Plugin selecting the ‘Scatter Plot’ for the Plot Type,
‘Distribution Analysis’ as the Layer, ‘LEN’ for the X Field and ‘Cum_Freq’ for
the Y Field. In the setting tab select ‘Logarithmic’ for both X Axis Mode and Y
Axis Mode to show a power law distribution.
 For histograms of fracture size distributions use the DataPlotly plugin, select
Plot Type as ‘Histogram’ and X Field as Shape_Length

5

3.3 Topological Analysis
3.3.1

Branches and Nodes
 Branch and node types can be automatically extracted using the ‘Branches
and Nodes’ tool.
 The inputs for this tool are the fracture network polylines, the sample area(s)
polygon, and optionally an interpretation boundary polygon can be used.
 The interpretation boundary is important as it defines the limit to which the
fracture network can be interpreted. Any fracture that intersects the
interpretation boundary polygon creates an edge node.
 The outputs of this tool are two new feature classes: Point Feature Class for
Nodes; Polyline Feature Class for Branches.
 The feature classes will have corresponding attribute tables detailing the
different node and branch type, each node and branch.
 Nodes identified as errors mean that the network has some inconsistent
digitized fracture polylines. This can be useful for identifying if the network
needs repairing.

3.3.2

Topological Analysis and Plots
 Once the branch and node feature classes have been extracted in workflow
3.3.1, specific topological parameters can be calculated using the ‘Topology
Parameters’ tool.
 The inputs into this tool are the extracted branch and node feature classes as
well as the sample area(s) polygon.
 A duplicate polygon feature class of the sample area(s) is output with a
number of calculated parameters added to the attribute table for each saaple
area, such as node and branch counts, 1D and 2D fracture intensity,
connecting node frequency, connections per branch, connections per line…
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 The ‘Topology Parameters’ output feature class can be used to create
triangular plots of the different node and branch proportions using the
DataPlotly Plugin. Select Plot Type as Ternary Plot, populate the X, Y and Z
fields with I,Y,X or I –I, I - C and C – C and hit Create Plot.
 Each sample area will be plotted as a dot that may be selected and visualized
interactively within the map window.

3.4 Spatial Analyses
3.4.1

Grid Sampling and Contour Plots
 A network of polylines can be sampled by a grid within the interpretation
boundary polygon using the ‘Contour Grid’ tool.
 The tool outputs a polygon feature class of grid cells within the
interpretation boundary that systematically sub-samples the network and
can be used later to create a contour plot illustrating spatial variations in
network properties.
 The tool allows the user to specify the size of the grid cells as well as applying
a search radius for sampling branches and nodes associated with each grid
cell.
 Branches and nodes should be extracted using the’ Branches and Nodes’
tool, following workflow 3.3.1, by using the grid cell polygon feature class as
the input for the sample areas.
 This extracts branches and nodes for every grid cell using the search radius
to define a circular sample region.
 Topological parameters can be calculated following workflow 3.3.2, by using
the extracted branches and nodes for each grid cell as inputs and the grid cell
polygon feature class.

7

4.0 Contact Information & Feedback
Please report any bugs or requests for enhancements on the GitHub NetworkGT repository issues tab
https://github.com/BjornNyberg/NetworkGT/issues

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Author                          : Bjørn Burr Nyberg
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Create Date                     : 2019:02:06 18:30:42+01:00
Modify Date                     : 2019:02:06 18:30:42+01:00
Producer                        : Microsoft® Word 2016

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