New release of qProf

qProf is a QGIS plugin for creating topographic and geological profiles.
A new version has been just released at: https://github.com/mauroalberti/qProf
This new version allows to create multiple topographic profiles, when the input profile lines are defined in a source line layer.
An example of a created profile is below.

To download the zipped plugin folder:

https://github.com/mauroalberti/qProf/releases

 Installation instructions are available at the main page:

https://github.com/mauroalberti/qProf

It's your fault

If you want to display your georeferenced faults in stereonets using QGIS you can use also the new functionalities in the geocouche plugin.

It uses apsg by Ondrej Lexa (apsg vers. 0.4.3 is incorporated in the plugin) for plotting geological data in stereonets. It allows to plot normal and reverse faults, while pure transcurrent faults are not explicitly treated in the used apsg version.

Input fault data format can follow two alternative formats:

1. slickenline dip trend and plunge, plus movement sense ("N" for normal faults and "R" for reverse faults)
2. rake angle according to the Aki & Richards (1980) convention (see Fig 1).

Fig. 1. Rake angle convention as defined from Aki & Richards (1980). Originally Figure 1 in Alberti (2005).

Take note that if you provide both line trend/plunge/movement sense and rake angle, rake angle takes precedence and shadows the data provided in the trend/plunge/movement sense format.

Now an example of using the geocouche tools for faults, using fault data stored in a point layer (this same layer is provided as a shapefile in the example data folder in the gihub repository).

You define the input data with the "Input data" button.  If you choose a (point) layer as source and there is a selection in the layer, only selected points will be considered.

Fig. 2. Example data with three records selected in a point layer, plus, on the right, the geocouche plugin activated.

 In the "Layer" tab of the input windows, you define the source fields for the different data types. Remember that definining (also) rake would override any data defined in the line orientation trend/plunge/movement sense fields.

Fig. 3. Definition of input fields for record dip direction, dip angle and rake angle.

You define which type of data to plot for the "plot data" button. You could also previously have changed the default plot style via the "Plot style" button.
Here we plot faults with slickenlines. Also T-L diagrams are available.

Fig. 4. Choice of faults with slickenlines data type for stereonet plot.

Et voilà..

Fig. 5. The stereonet of the faults and slickenlines data is displayed on the right.

Clear the stereonet with "Clear stereonet". Obviously you can suporpose multiple plots into a single stereonet.
Save a figure with the tool from "Save figure" button.

To install the plugin, clone the repository or download and extract the zip file from https://github.com/mauroalberti/geocouche/releases in your local QGIS Python plugin folder (for instance: /home/mauro/.qgis2/python/plugins/geocouche) and activate the plugin in the installed section of QGIS "Manage and install plugins" command. 

For any question: alberti.m65 at gmail.com

 

References

Aki, K., Richards P.G., 1980. quantitative Seismology Theory and Methods. Vol. I, W.H. Freeman and Company, San Francisco, CA,, 557 pp.

Alberti, M., 2005. Apllication of GIS to spatial analysis of mesofault population. Computers & Geosciences, 1249-1259.

Plotting geological attitudes in stereonets using QGIS

A new plugin for QGIS, geocouche, allows to plot geological data attitudes stored in stereonets, using the plotting utilities provided by the apsg module by Ondrej Lexa. Data can be stored in geological layers or entered as text, and plotted as great circles or axis. The current release, as of April, 4th,  is vers. 1.0 and  can be downloaded from: https://github.com/mauroalberti/geocouche/releases

How it works? The following description derives from the tool help. 
With the current geocouche  release, it is possible:

1. to calculate the angles between planes stored in a layer and a reference plane
2. to plot data from layers or texts in stereonets

These two tools are available from the QGIS plugin interface.

Fig. 1. geocouche interface.

Geological angles

This tool allows to calculate the angles (as degrees) between a reference plane and the (eventually selected) features in a point layer (Fig. 2).

Fig. 2. Geological angles calculation interface.

It can be applied to determine the degree of misalignement between a reference (for instance, regional) measure and local geological measures.

Definition of parameters

The user has to define the two fields storing the azimuth (dip direction or RHR strike) and the dip angle of each feature, the attitude of the reference plane, and the name of the output shapefile with a new field storing the calculated angle (Fig. 3).

Fig. 3. Definition of parameters for angle calculation.

Geological stereonets

It allows to produce stereonets depicting geological plane and axis attitudes (Fig. 4). There are three steps:

1. Choice of input data
2. Definition of plot style
3. Data plotting

Fig. 4. Stereonet interface.

Choice of input data

It is possible to use input data from data stored in a point layer (Layer tab, Fig. 5) or to use text input (Text tab, Fig. 6).

Input from point layer

When using a point layer (already loaded in the TOC), plane and/or axis attitudes are defined via the fields storing their values (Fig. 5). When a selection is defined, only the selected features will be considered.

Fig. 5. Input from point layer interface.

Input from text

The input can be inserted into a text window (Fig. 6), defining if data consist of:

• planes

• axes

• planes and axes

Fig. 6. Input from text interface.

Another option to take care of, is,  for plane data, whether orientations are expressed using dip direction or RHR strike.

Plot style

Styles can be defined for both great circles and poles: color, width/size, line/marker style, and transparency (Fig. 7). Settings are stored in memory.

Fig. 7. Plot style interface.

Stereonet plotting

Plots can use a new or a pre-existing stereonet (provided it has not been previously closed) (Fig. 8).

Fig. 8. Stereonet plot interface.

Planes can be plotted as great circles or as plane normals, axes as poles or as normal great circles. An example of stereonet is shown in Fig. 9.

Fig. 9. Stereonet example.

A Linux tool for calculating local best-fit plane attitudes from geological traces

The topographic traces of geological surfaces store information on the 3D attitudes of the geological surfaces. Knowing the coordinates of the intersection points between a topographic surface and a geological surface, it is therefore possible to estimate the local attitudes of a geological surface.

 

The tools

 

A short description of geoSurfDEM: it is composed of two tools, IntersectDEM and the new BestFitGeoplanes.
The former allows to calculate the intersection points between a geological surfaces (stored in the VTK format) and a DEM. The latter, that will be described in the current post, allows to estimate the local attitudes given a set of 3D points, all deriving from the intersection between a single geological surface and a topographic surface. BestFitGeoplanes is developed using C++ and Fortran. The algorithm uses Singular Value Decomposition (SVD) in order to invert the local traces into local best-fit planes. 

The input data is constituted by a set of points (their x, y and z coordinates), all related to a single, continuous geological surface. How to process them in order to derive the local attitudes? Since the source points are unconnected points (not lines), all deriving from a single, continuous surface, the 2D space is discretized into a raster, using a user-defined cell size.
Based on the points falling into a cell, we have three possible cases:

1. no points falling into the cell;
2. one or two points falling into the cell;
3. three or more points in the cell.

In the first and second case, no attitude inversion via SVD is possible.
In the third case, when the points are not all collinear, a solution is provided by the SVD method. This solution is attributed to the grid cell.
The algorithm output will therefore consist in a gridded set of points for which the local attitudes have been inverted.
 
What is the difference with deriving the attitude via a spatial interpolation using for instance kriging? These interpolations implicitly assume a 2.5D surface and do not allow 3D surfaces. Geological surfaces, on the other hand, due to folding, can be 3D surfaces, i.e. with more then one point for each x-y position. Local inversion via SVD does not constrain the geological surfaces to be 2.5D,  but that may be locally modeled via a planar surface.

 

Compilation

 

This application is developed in Linux and is available at: https://github.com/mauroalberti/geoSurfDEM.
A makefile is available for compiling this tool in a Linux environment.
The compilation sequence is:
cd path/to/source/files
make
make clean

Lapack and BLAS libraries must be available. The makefile assumes that Lapack is available in usr/lib/lapack (with name lapack) and BLAS in usr/lib/libblas (name blas). Modify the makefile accordingly, to adapt to your settings. Alternatively, an example of commands to build it (always in a Linux environment and with same libraries settings) is in https://github.com/mauroalberti/geoSurfDEM/blob/master/BestFitGeoplanes/compile

 

Use

 

Having compiled the application, it is possible to run it as console application (Fig. 1). The only user interaction after launching the application is providing a parameter file name ("param.txt" in Fig. 1 example).

Fig. 1. Example of a run of the application.

 

The input parameter file is a text file that lists six pieces of information:

1. the path of text file storing the 3D coordinates (x, y and z) of the intersection points of a single, continuous, geological surface;
2. the number of header lines in the file referenced in point 1;
3. the path  of the text file in which the georeferenced results will be stored;
4. the path to the analysis report file;
5. the path of the output grid (in ESRI ASCII grid format) that will list the number of intersection points for each grid cell;
6. the output grid cell size;

 An example is available in https://github.com/mauroalberti/geoSurfDEM/tree/master/BestFitGeoplanes, in the param.txt file:

/home/mauro/Documents/Ricerca/Codice/Geostrutturale/geoSurfDEM/test_data/BestFitGeoplanes/inters_malpi_135_35.csv
1
/home/mauro/Documents/Ricerca/Codice/Geostrutturale/geoSurfDEM/test_data/BestFitGeoplanes/bfg_malpi_13535_100.txt
/home/mauro/Documents/Ricerca/Codice/Geostrutturale/geoSurfDEM/test_data/BestFitGeoplanes/rep_malpi_13535_100.txt
/home/mauro/Documents/Ricerca/Codice/Geostrutturale/geoSurfDEM/test_data/BestFitGeoplanes/pts_malpi_13535_100.asc
100 

The application output is represented by the three files listed in points 3-5 of the previous list. The more important is the inverted result file (point # 3), that consists in a csv file listing a few fields (see Fig. 2):

1. x: x coordinate of the cell grid center;
2. y: y coordinate of the cell grid center;
3. pt_num: number of points used for the inversion. Required minimum is 3.
4. dip_dir: inverted dip direction for geoplane points in cell;
5. dip_ang: inverted dip angle for geoplane points in cell;
6. x_range: spatial range along the x-direction (E-W) for the inverted points in the considered cell;
7. y_range: spatial range along the y-direction (N-S) for the inverted points in the considered cell;
8. z_range: spatial range along the z-direction (vertical) for the inverted points in the considered cell;
9. pseudo-volume: "pseudo"-volume defined by the inverted points in the cell, given by the product of the three previous ranges (i.e., x_range, y_range and z_range) - possibly removed in successive releases.

Fig. 2. Tabular view of the content of the inversion result file, as viewed by importing the file in QGIS.

 

A theoretical case study 

 

This post presents a practical assessment of the result, by using a theoretical surface for which the expected local attitudes are known (currently, as of February 2017, all example data are available at https://github.com/mauroalberti/geoSurfDEM/tree/master/test_data).
A theoretical plane has been generated using simSurf, with dip direction equal to 135° and dip angle of 35°.
This plane, saved in VTK format from within simSurf, has been used as input plane to be intersecated with a natural topographic surface, of the Mt. Alpi zone (Lucania, Southern Italy), using the IntersectDEM of geoSurfDEM.
The resulting intersection points are saved as a csv file, that can be used as input for the BestFitGeoplanes. The intersection points, to be used for the best-fit-plane local inversions, are represented in Fig. 3.

Fig. 3. Input points (yellow) representing the theoretical intersection between a geoplane oriented 135°/35° (dip dir. and dip angle) and a DEM topography (Mt. Alpi zone, Lucania, Southern Italy). Visualization using QGIS.

 

Using BestFitGeoplanes with the previously described param.txt file, we obtain a result that, for the georeferenced point part, imported in QGIS is shown in Fig. 4.

Fig. 4. The same as in Fig. 3, plus superposed the gridded points with inverted results (orange dots). Visualization with QGIS.

 

How much the inverted results conform to the theoretical input source, that as said is a plane with a dip direction of 135° and a dip angle of 35°?
A stereoplot, created with the geocouche plugin for QGIS, illustrates the degree of  concordance between the source attitude (135°/35°, blue great circle in Fig. 5) and the inverted local attitudes (semi-transparent orange great circles in Fig. 5).
The majority of inverted data conform closely to the expected result, while a few inversions show a minor deviation from the expected result.

 

Fig. 5. Stereonet representing the inferred local plane attitudes as semi-opaque orange great circles, and the source geological plane attitude (135°/35°) as blue great circle. Created with geocouche.

The deviations of the inverted results from the expected value were calculated using the "Geological angles" of geocouche and the statistics calculated with QGIS (see Fig. 6). The maximum is 9.3° and the minimum almost zero, while the median and mean deviation values are lower than 0.5°. The standard deviation is about 1.2°. So in general we can be quite confident in the generated results. More in-depth analyses of the deviations of expected-versus-inferred results could be the subject of a still to-be-written paper.

Fig. 6. Statistics for angular deviations of the calculated results from the theoretical test case.

Edits

2022-12-29: improved paragraph styling; modified input parameters description (items 5 and 6)