OR/13/050 Model workflow
| Gow, H, Cripps, C, Thorpe, S, Horabin, C, and Lee, J R. 2013. Model metadata report for the Somerset levels 3D geological model. British Geological Survey Internal Report, OR/13/050. |
GSI3D geological modelling software uses a series of files to setup the working project file. These are:
- Geological Vertical Section (GVS) — a file which contains the stratigraphical order of the geological units
- Geological Legend (GLEG) — a file describing the colours for the geological units
- Borehole ID (BID) — a file containing the location and start height of each borehole
- Borehole Log (BLG) — a file containing the geological information found within the borehole and its depths
- DTM — capping surface to the model
- Rockhead Elevation model
- Map data
The standard GSI3D workflow (Kessler and Mathers, 2004[1]; Kessler et al., 2009[2]) allows the modeller to create cross-sections across the project area by connecting boreholes and correlating the baselines for each of the geological units. Once a series of cross-sections have been created a distribution for the outcrop and subcrop for each unit can be described. Using both the information from the cross-sections and the distribution of each unit a calculation algorithm creates the triangulated surfaces for the top and base of each unit. The modeller can then view all the units in 3D and iteratively return to the cross-section to make amendments or add further cross-sections to refine the model. This whole process is a standard methodology for creating superficial geological models and is documented in the following publications (Kessler & Mathers, 2004[1]; Kessler et al 2009[2]).
Two exceptions to the standard methodology have been employed to enable a better model to be produced. Firstly, alluvium can be a very thin and discontinuous unit and this can cause problems with the model calculation. To improve the quality of model calculation, a depth of 2 m has been applied to the DTM and exported as a grid of points. This grid has been trimmed by the alluvium surface distribution polygon (which was further buffered by 2 m around its outline) and where any cross-section correlation has been drawn, a buffer distance of 100 m has been applied to the section. The resulting grid has been used to form the base to the unit. The second exception relates to the model calculation of bedrock units and uses a similar gridding technique. Due to the nature of the geology (some units extend to depths greater than the base of the model) an arbitrary base has to be drawn to create a neat model base. This has been drawn at -28 m OD. For each of the bedrock units the distribution envelope has been taken and applied to a -28 m grid to create a flat surface for each unit. This surface has then been loaded into the model and the calculation takes into account the base surface together with the correlation points along all sections.
References
- ↑ 1.0 1.1 KESSLER, H, and MATHERS, S J. 2004. Maps to models. Geoscientist, Vol. 14, 4 6.
- ↑ 2.0 2.1 KESSLER, H, MATHERS, S J, and SOBISCH, H-G. 2009. The capture and dissemination of integrated 3D geospatial knowledge at the British Geological Survey using GSI3D software and methodology. Computers & geosciences, Vol. 35, 1311–1321.