A QGIS and ArcGIS Pro plugin for subsampling geological orientations, faults, and polygons. This plugin provides various methods to reduce the complexity of geological datasets while preserving important structural information.
GeoSubSampler is designed to help geologists and GIS professionals manage large geological datasets by providing intelligent subsampling methods. The plugin supports processing of:
- Structural orientation data (dip/strike measurements)
- Geological polygons (rock units, formations)
- Fault and contact lines
- Install the QPIP plugin through QGIS Plugin Manager
- Download the plugin files (works with QGIS 3.x and 4.x)
- Place them in your QGIS plugins directory
- Restart QGIS. QPIP will offer to install any missing Python packages listed in
requirements.txt - Enable the plugin through QGIS Plugin Manager
- The plugin will appear as a dockable widget in QGIS
An ArcGIS Pro equivalent of the plugin is in the ARCGIS folder. It is a Python toolbox
(ARCGIS/GeoSubSampler.pyt) whose Launch GeoSubSampler GUI tool opens a Tkinter window with the same
groups and settings as the QGIS dock widget (orientation subsampling, fault processing, geology polygons and
Töpfer & Pillewizer scaling), using the same calcs code. The window lists the point, line and polygon
layers in your project, and results are added to the map automatically with the symbology of the layer they
were made from.
The ArcGIS Pro Python environment needs geopandas (not included by default) and, if not already installed,
scikit-learn, networkx, scipy, matplotlib, fiona and triangle. See ARCGIS/README.md for
installation and usage notes.
The toolbox has a tool that sets up the environment for you. ArcGIS Pro's default environment
(arcgispro-py3) cannot be changed, so the tool clones it into a new environment called
arcgispro-py3-geotools, installs the missing packages, checks that they all import, and makes the new
environment the one ArcGIS Pro uses.
Note: the tool creates a new environment,
arcgispro-py3-geotools, as a copy ofarcgispro-py3. It does not changearcgispro-py3or any other environment you already have. It then makes the new environment the one ArcGIS Pro uses, so restart ArcGIS Pro when it has finished. To go back, choose another environment in Project > Package Manager and restart ArcGIS Pro. The tool cannot change or delete the environment ArcGIS Pro is using at the time, so to run it again with Delete the environment first, switch to another environment and restart first.
- In the ArcGIS Pro Catalog pane, go to Toolboxes > Add Toolbox and select
ARCGIS/GeoSubSampler.pyt. - In the GeoSubSampler toolbox, open Setup > Set Up Python Environment and click Run. It needs an internet connection and takes about 10 minutes. Click View Details in the Geoprocessing pane to follow its progress.
- When it has finished, restart ArcGIS Pro, then run Launch GeoSubSampler GUI.
The same tool is in the SGTool, tomofast_x_q and GeoSubSampler toolboxes and installs what all three need, so you only need to run it once. Running it again only adds what is missing. Its options let you choose a different environment name, leave ArcGIS Pro's active environment unchanged (activate it later in Package Manager), or delete the environment and start again from a new clone.
The tool runs the script ARCGIS/setup_arcgispro_env.py, which can also be run from a Windows Command Prompt
(change the paths if ArcGIS Pro or this repository are somewhere else):
"C:\Program Files\ArcGIS\Pro\bin\Python\envs\arcgispro-py3\python.exe" "C:\path\to\GeoSubSampler\ARCGIS\setup_arcgispro_env.py"
- Layer Selection: Choose the point layer containing structural measurements
- Dip Field: Field containing dip angle values
- Type: Numeric field from selected layer
- Description: Angle of dip from horizontal (0-90°). If this field holds values outside 0-90° the tools stop with a message, because the Dip and Dip Direction/Strike fields have most likely been swapped
- Dip Direction/Strike Field: Field containing directional information
- Type: Numeric field from selected layer
- Description: Either dip direction (0-360°) or strike direction
- Dip Direction Checkbox: Toggle between dip direction and strike convention
- Description: Check if using dip direction, uncheck if using strike
- Polyline Layer: Layer containing geological contacts or boundaries
- Type: Line layer
- Description: Used for first-order subsampling relative to geological boundaries
Randomly samples a percentage of orientation points.
Parameters:
- Retain Percentage: Percentage of points to keep (0-100%)
- Type: Float
- Range: 0.0 - 100.0
- Description: Controls what fraction of the original dataset is retained
Averages the orientations within each grid cell (the normalised vector mean) and reports Kent distribution
statistics for the cell. Each output point sits at the mean position of the cell's measurements and carries
count, kappa (concentration) and beta (ovalness) attributes. (A plain grid-cell average is the same
calculation without kappa and beta, so it is no longer offered separately.)
Parameters:
- Grid Size (Kent): Grid cell size for Kent statistical averaging
- Type: Float
- Units: Layer units
- Description: Grid size for applying Kent distribution statistics
- Min kappa (optional): Keep a cell only if its Kent kappa (concentration) is at least this value
- Type: Float; leave blank (or 0) for no filter
- Description: Drops cells with a single measurement and cells whose orientations are scattered
(the thesis models used 5). Cells that survive carry
count,kappaandbetaattributes (-998 where undefined). Not applied by the Töpfer & Pillewizer tool.
Applies Kent statistics while removing the largest outliers within each grid cell.
Parameters:
- Grid Size (Kent Outlier): Grid cell size for Kent averaging with outlier removal
- Type: Float
- Units: Layer units
- Outlier Threshold: Threshold for outlier identification and removal
- Type: Float
- Description: Statistical threshold for identifying and removing outliers
- Iterative (experimental): Remove several outliers per cell instead of one. Points are taken out in order of how much their removal raises Kent kappa (up to half the cell) and the sequence is cut at its largest kappa jump, but only if that jump is at least 5 times the typical step; otherwise nothing is removed (removing any point from a small sample raises kappa a little, so a plain "stop when kappa stops rising" rule over-trims). This differs from the Carmichael method below, which orders points by angle from the cell mean.
Kent averaging that can remove several outliers per grid cell (Carmichael & Ailleres, 2016), where
Kent Outlier removes at most one. In each cell the measurements are ranked by angle from the cell's mean
direction (farthest first) and removed one at a time while Kent kappa is recomputed; everything removed up
to the biggest jump in kappa is treated as outliers (at most half the cell). Cells with 3 or fewer
measurements are skipped. Output points carry count, kappa, beta and n_removed attributes.
Parameters:
- Grid Size (Carmichael): Grid cell size, in layer units. "Auto-fit to N pts" works as for the other grid methods.
Retains orientation points based on proximity to geological contacts and angular relationships.
Parameters:
- Distance Buffer: Buffer distance around geological contacts
- Type: Float
- Units: Layer units
- Description: Points within this distance of contacts are prioritized
- Angle Tolerance: Angular tolerance for point retention
- Type: Float
- Units: Degrees
- Description: Tolerance for angular relationships between measurements and contacts
Merges connected fault segments based on geometric criteria.
WARNING: This is not particulary optimised and may take hours to complete on large (>10k polylines) datasets
Parameters:
- Distance Tolerance: Maximum distance between line endpoints for merging
- Type: Float
- Units: Layer units
- Description: Endpoints closer than this distance are candidates for merging
- Search Angle Tolerance: Maximum angle difference for parallel lines
- Type: Float
- Units: Degrees
- Description: Lines with orientations within this tolerance are considered parallel
- Join Angle: Minimum angle at connection points
- Type: Float
- Units: Degrees
- Description: Rejects connections that create angles smaller than this value
Filters fault lines based on minimum length criteria.
Parameters:
-
Minimum Fault Length: Calculate length for faults
- Does not actual filter, just creates new layer
-
Fault Graph: Calculate Network Graph parameters for fault network
- Does not actual filter, just creates new layer
-
Fault Stratigraphic Offset: Maximum stratigraphic offset accross fault for start-, mid- and end-points for fault network
- Does not actual filter, just creates new layer
Removes small polygons and fills holes based on area thresholds.
Parameters:
- Minimum Polygon Diameter: Threshold diameter for polygon retention
- Type: Float
- Units: Kilometers
- Description: Polygons with equivalent diameter smaller than this are removed/merged
- Node Tolerance: Tolerance for node snapping during processing
- Type: Float
- Units: Layer units
- Description: Distance tolerance for merging nearby vertices
Define the hierarchy for polygon merging decisions:
- Priority 1-5 Fields: Stratigraphic fields in order of importance
- Type: Attribute fields from polygon layer
- Description: Used to determine which polygon attributes are preserved during merging
- Order: Priority 1 has highest importance, Priority 5 has lowest
- Lithology Field: Field containing lithological information
- Type: Attribute field
- Description: Used for lithological classification during polygon processing
- Ignore Field: Field identifying polygons that are removed by triangulation then merging, not by merging
- Type: Attribute field
- Ignore Codes: Comma-separated list of codes identifying dykes/intrusions/alluvium that are best removed by triangulation, given their aspect ratio
- Format: Text list (e.g., DY1, DY2, INTX-D )
- Description: Special processing applied to polygons with these codes
- Series Checkbox: Enable processing of multiple scales
- Description: When checked, creates multiple outputs at different scales
- Increment Value: Step size for series processing
- Type: Float
- Units: Same as minimum diameter
- Description: Increment between successive processing scales
- Area Tolerance (m2): Area threshold for exterior vertices
- Description: Decimates map polygons and associated faults composed of line segments to a similar curves with fewer vertices. Vertices to be removed are those whose triangular area (area defined by the vertex and its two neighbours) exceeds the threshold. When a polygon vertex is to be removed that coincides with a fault vertex, the two will be removed together to maintain their topological relationships.
The TP scaling rule: TN = ON * (OS/TS)^(x/2)
- TN — target number of objects after generalisation
- ON — original number of objects before generalisation
- OS — original map scale denominator (e.g. 50 000)
- TS — target map scale denominator (e.g. 500 000)
- x — object type: 1 = points, 2 = lines, 3 = polygons
This will use the currently set parameters for each type of data to calculate a series of subsampling calculations to try to match the TP rule. The Old Scale/New Scale ratio defines the amount of subsampling, and Increment term defines how many steps (and hence sets of layers) will be calculated.
- Geographic Coordinates: Grid sizes are automatically converted from meters to degrees (÷110,000)
- Projected Coordinates: Grid sizes are used directly in the specified units
- Input layers must be saved as shapefiles on disk
- The plugin cannot process temporary or memory layers
Output files follow the pattern: [original_name]_[method]_[parameters].shp
- If a file with the same name exists, a random 5-digit suffix is added
- Segment Merging: Very slow for large datasets (>1 second per object)
- Large Datasets: Consider using subsampling methods before applying computationally intensive operations
The plugin includes validation for:
- Missing required fields
- Invalid layer selections
- File access permissions
- Coordinate system compatibility
- QGIS Python API (PyQt, qgis.core)
- Shapely (2.0 or later; its STRtree is used for polyline merging)
- NumPy
- pandas
- GeoPandas
- Fiona
- SciPy
- Matplotlib
- scikit-learn
- NetworkX
- triangle (only needed for polygon triangulation)
These are listed in requirements.txt and are installed automatically by QPIP. Most of them ship with QGIS; scikit-learn, NetworkX and triangle usually need to be installed.
This program is free software under the MIT License.
- Add Ranee's code for simplification of fault/polygon sets preserving topology
- Simplify fault arrays suing topological constraints
Ranee Joshi-most calculation code
Email: raneejoshi@gmail.com
Mark Jessell-some calculation code & GUI
Email: mark.jessell@uwa.edu.au@gmail.com
- Begin Date: 2025-07-28
- Generated by: Plugin Builder
- Plugin Builder: http://g-sherman.github.io/Qgis-Plugin-Builder/
Note: This plugin requires layers to be saved as shapefiles for processing. Ensure your data is properly saved before attempting to use the subsampling functions.