Introducing Explicit Structured Grids in VTK and ParaView

Data Structure

An explicit structured grid is a new data structure in VTK sharing properties of both structured and unstructured grids. This new dataset is well adapted to represent the reservoir grids that are well known in the Oil&Gas domain.

The data structure of an explicit structured grid uses a structured coordinate system (i, j, k) to determine cell neighborhoods, which also allows the support of cell blanking. At the same time, the geometry of each cell is explicitly defined by its vertices (see Figure 2). This way of defining cells allows to define not only curvilinear grids but also grids with more complex topologies. In an explicit structured grid, cells can be neighboring but don’t need to be connected. These discontinuities in the geometry can model small and large cracks between cells with the same efficiency than unstructured grids, without the need to increase the cell resolution. In contrast to unstructured grids however, explicit structured grids have the advantage of their underlying regular structure for better performance in a data parallel context (see Figure 3).

Pros & Cons

(SG = vtkStructuredGrid; UG = vtkUnstructuredGrid; ESG = vtkExplicitStructuredGrid)

Filters

For now the new data structure comes with an optimized crop filter, several converters and a super class to develop additional explicit structured grid algorithms. The converters make the new data structure more accessible to users by enabling them to easily transform their existing data into explicit structured grids.

The converters include the following:

• To/From UnstructuredGrid;
• From ImageData;
• To PolyData (i.e. extracts the surface mesh);
• Explicit Structured Grid generator source.

Finally, a new data source was also added to Paraview to quickly generate different explicit structured grid reservoir data (see Figure 4).

Data Format

Thanks to the included conversion filters and the data structures similarities to unstructured grids, there is no need for a data format specific to explicit structured grids. Instead, explicit structured grids save their data as unstructured grids without any loss of information.

The ParaView Plugin

ParaView 5.7.0 comes with a new plugin simply called “ExplicitStructuredGrid” that provides the procedural source and some filters (converters to/from UnstructuredGrids, efficient slicing, cropping and cells extractor on structured coordinates criteria) to process the new dataset.

This work was supported by Total SA

Developments were done by Kitware SAS, France