Unstructured Grid

What is an Unstructured Grid?

An unstructured grid, or UGrid for short, is spatially referenced information made up of points (x, y, z locations). An unstructured grid may also have information about connections between the points. The connections between the points may define lines and faces; the faces may also be connected to define volumes.

Vocabulary

Some individuals have strong feelings about how the words 'grid' and 'mesh' should be used and what type of geometry each should refer to. Some prefer to reserve the word grid for structured spatial data and the word mesh for unstructured spatial data. Traditionally the XMS programs (GMS, SMS) have followed this same approach.

Therefore, UGrids were introduced into XMS as a new type of geometry that could represent both grids and meshes (as defined by XMS).

The vision for UGrids is to encompass all of the functionality present in 2D Grids, 2D Meshes, 2D Scatter Points, 3D Grids, 3D Meshes, 3D Scatter Points, and TINs without having separate modules and tools. Additionally, UGrids can also be used with other types of "grids" that were previously not supported in XMS: quadtree grids and voronoi grids. Future users of XMS will not have to learn what differences exist between TINs, meshes, grids, and scatter or wonder why some tools or commands only operate on scatter sets but not meshes. Display options, tools, and workflows will functions with UGrids.

Confusion can also exist by the words used to describe components of a grid or mesh: points vs. nodes and cells vs. elements. Traditionally in XMS, different names have been used for different modules. For example, the x, y, z locations for scatter points are referred to as points in contrast to the locations of a mesh being referred to as nodes while the locations of a grid have either been ignored or been referred to as nodes. Also, the word element has been used to describe the connections between points in a mesh and the word cell has been used to describe the connections between points in a grid.

UGrids refer to the x, y, z locations as points and connections between points are referred to as cells.

UGrids defined by points only

scatter points 3d scatter points

2D UGrids

meshes, grids

3D UGrids

3d meshes, 3d grids

Constrained UGrids

Quadtrees, 2d, 3d, all triangles...

Why UGrids?

• One set of tools for working with all types of grids
• One set of display parameters for visualizing the grids
• One type on grid to be used with the toolbox
• Smaller code base with increased test coverage to make sure the tools and visualization works
• Support for point datasets and cell datasets