SecInterp Plugin Documentation

SecInterp is a QGIS plugin designed to assist in geological interpretation by extracting data along a cross-section line. It integrates topographic data from DEMs, geological units from outcrop polygons, and structural measurements from point layers.

Requirements

To use SecInterp, you need the following layers in your QGIS project:

  1. Raster Layer (DEM): A Digital Elevation Model to extract the topographic profile.

  2. Crossline Layer: A line vector layer defining the location of the cross-section.

  3. Outcrop Layer (Optional): A polygon vector layer representing geological units (outcrops).

  4. Structural Layer (Optional): A point vector layer containing structural measurements (strike and dip).

Layer Data Requirements

Raster Layer (DEM)

The Digital Elevation Model must meet the following requirements:

  • Data Type: Single-band or multi-band raster layer

  • Band Selection: You can select which band to use for elevation (default is band 1)

  • Data Format: Any GDAL-supported raster format (GeoTIFF, IMG, ASCII Grid, etc.)

  • Cell Values: Numeric elevation values (typically in meters or feet)

  • NoData Handling: NoData values should be properly defined in the raster metadata

  • Coordinate System: Must use a projected CRS (not geographic) for accurate distance calculations

  • Resolution: The plugin automatically adapts sampling to the raster resolution for optimal profile extraction

  • Coverage: Should cover the entire extent of the crossline

Crossline Layer

The cross-section line layer must meet the following requirements:

  • Geometry Type: LineString or MultiLineString

  • Features: Typically contains a single line feature defining the section location

  • Line Orientation: The line direction determines the profile orientation (start to end point)

  • Coordinate System: Must use the same CRS as the raster layer (projected CRS recommended)

  • Data Quality: Line should be continuous without gaps

  • Length: No specific length restrictions, but very long sections may result in large output files

Outcrop Layer (Geology)

The outcrop layer must meet the following requirements:

  • Geometry Type: Polygon or MultiPolygon

  • Required Fields: At least one text or numeric field containing the geological unit identifier (e.g., unit name, code, or formation name)

  • Field Format: * Field can be of type String, Integer, or any other attribute type * Examples: “Qal” (Quaternary alluvium), “Kg” (Cretaceous granite), “Unit_1”, etc.

  • Coordinate System: Must use the same CRS as the crossline layer, or a compatible projected CRS

  • Data Quality: Polygons should be topologically correct (no gaps, no overlaps if representing continuous geology)

Structural Layer

The structural layer must meet the following requirements:

  • Geometry Type: Point

  • Required Fields: Two numeric fields containing: * Strike: Azimuth direction of the strike line (0-360 degrees) * Dip: Dip angle from horizontal (0-90 degrees)

  • Field Format: * Both fields must be numeric (Integer or Real/Double) * Strike: 0-360° (geographic azimuth, where 0° = North, 90° = East) * Dip: 0-90° (angle from horizontal plane)

  • Coordinate System: Must use the same CRS as the crossline layer

  • Spatial Distribution: Points within approximately 100m of the crossline will be projected onto the section

Usage

  1. Select Layers: * Choose the Raster Layer for elevation. * Choose the Crossline Layer for the section line. * (Optional) Select the Outcrop Layer and the field containing the unit name/code. * (Optional) Select the Structural Layer and the fields for Dip and Strike.

  2. Configuration: * Band: Select the raster band to use for elevation (default is 1). * Output Folder: Choose a directory where the results will be saved.

  3. Process Data:

    The plugin provides four buttons with different actions:

    • OK: Processes the data (generates CSV files and preview) and closes the dialog window.

    • Apply: Processes the data (generates CSV files and preview) but keeps the dialog window open. Use this to process data and review results without closing the plugin.

    • Save: Saves the profile data as Shapefiles (topo_profile.shp, geol_profile.shp, structural_profile.shp) without generating CSV files. The dialog remains open after saving. Use this to export geometric representations of the profiles.

    • Cancel: Closes the dialog window without processing or saving any data.

Outputs

The plugin generates the following files in the selected output folder:

  • topo_profile.csv: CSV file containing distance and elevation points along the section.

  • geol_profile.csv (if Outcrop Layer selected): CSV file with distance, elevation, and geology code.

  • geol_profile.shp (if Outcrop Layer selected): Shapefile (LineString) representing the geological units draped over the topography.

  • structural_profile.csv (if Structural Layer selected): CSV file with projected structural data.

  • structural_profile.shp (if Structural Layer selected): Shapefile (LineString) representing apparent dip lines projected onto the section.

Indices and tables