Anomaly Extractor

An algorithm to automatically vectorize anomalies caused by archaeological features in magnetograms and calculate a number of statistical parameters.

The tool is being developed by the German Archaeological Institute.

The source code is a result of the QGIS modeler used for designing the algorithm workflow.

See an article about the tool:

Goldmann, L. and Komp, R. (2025), The Anomaly Extractor—An Open-Source GIS-Tool for Object-Based Image Analyses of Large-Scale Geomagnetic Data.

Archaeological Prospection.

https://doi.org/10.1002/arp.1987

Installation

In QGIS open Processing Toolbox and choose Add Model to Toolbox ...

Tested QGIS Version: 3.34.8

Usage

Input parameters

• input_threshold
  
  Formula to define at which threshold (usually in nT) anomalies will be vectorized:
  

  • 1.1) Default: if(abs("A@1")>5,1,0/0) = +/- 5 nT
    
  • 1.2) Example 1: if("A@1"<-5,1,0/0) = -5 nT
    
  • 1.3) Example 2: if("A@1">5,1,0/0) = +5 nT
    
    Notes:
    • The cipher "5" in these examples is the relevant term, which defines the desired theshold (to be modified according individual needs).
      
    • The term "0/0" is an expression for "NULL".
      

• input_extent
  
  Optional, used to run algorithm on a part of a dataset only:

  • 2.1) Default: No input ([0,0,0,0]) = uses the entire input raster.
    
  • 2.2) Possible inputs are manual coordinates, mask layers, map canvas extent or manually drawn rectangles.

• input_holesize
  
  Optional, deletes interior holes/rings within a vectorized polygon that are smaller than the given value in the unit of the chosen CRS:

  • 3.1) Default: 1 (usually m²)
    
  • 3.2) Delete all rings: 0
    
  • 3.3) Option: Float, 0 - 100000
    

• input_raster
  
  The input raster has to be a GeoTiff holding numeric measurement values, usually in nT.
  

Outputs

• ExtractedAnomalies
  
  Extracted anomalies as single polygon features.
  

Algorithm author: Rainer Komp/Lukas Goldmann 2024-08-01

Help author: Lukas Goldmann 2024-08-01

Algorithm version: 1.6.4 2024-08-01