GMS:2D Grid Creation and Editing

2D Grid Module

2D Grid
Creating and Editing 2D Grids
Converting 2D Grids
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2D Grid Display Options
2D Grid Tool Palette
Cell Properties
2D Grid Commands

GMS provides two methods for creating 2D grids and multiple ways to edit a 2D grid.

Creating 2D Grids

Two types of 2D grids are supported by GMS, mesh centered and cell centered. The two main techniques used to create 2D grids are: the Create Grid command and the Map → 2D Grid command. A 2D grid can also be created from an existing 3D grid using the Grid → 2D Grid command in the Grid menu of the 3D Grid module. A GIS grid may also be imported.

Create Grid

A new grid can be created by selecting the Create Grid command from the Grid menu. This command brings up the Create Grid dialog. The options in the dialog are as follows:

• Origin, Length, Rotation – By default, the rows and columns of 2D grids are aligned with the x and y axes. However, grids can be rotated about the z-axis, if desired. Thus, the information needed to determine the overall size and location of the grid is the xy coordinates of the lower left corner of the grid (the lower left corner prior to rotation), the length of the grid in the x and y directions, and the rotation angle. The xy coordinates of the origin are entered in the Origin edit fields, the dimensions are entered in the Length fields, and the angle of rotation is entered in the field entitled Rotation about Z-axis.
• Bias – Several options are available for defining the number and locations of the cell boundaries. A bias can be defined which controls how the cell size varies from one cell to the next. For example, an X bias of 1.5 causes each cell to be 50% larger than the previous cell when moving in the positive x direction.
• Number of Cells – The total number of cells in each direction (number of rows or columns) can be defined by explicitly entering a number or by entering a base cell size and a limit cell size. The base and limit cell size options are used when a bias other than 1.0 is specified. The base cell size is the size of the first cell in the sequence. The cells are then generated by altering the cell size according to the bias until the limit cell size is reached. The remainder of the cells are constructed using the limit cell size.
• Type and Orientation – The controls at the bottom of the Create Grid dialog are used to define the type and orientation of the grid. The user can specify whether the grid should be a mesh-centered grid or a cell-centered grid. The orientation of the ij axes with respect to the XY axes can also be specified.
The Create Finite Difference Grid dialog

Map → 2D Grid

The Map → 2D Grid command is used to construct a 2D grid using the feature objects in a 2D grid coverage. When the Map → 2D Grid command is selected, the Create Grid dialog appears. If a grid frame has been defined, the size and location of the grid frame are used to initialize the fields in the Create Grid dialog. In most cases, these values will not need to be changed so simply select the OK button to create the grid. If a grid frame has not been defined, the size and location of the grid are initialized so that the grid just surrounds the currently defined feature objects. If desired, the grid dimensions can be edited prior to selecting the OK button to create the grid.

If one or more refine points are defined in the conceptual model (available when Refinement is selected in the Coverage Setup dialog), the number of rows and columns in the grid will be automatically determined when the grid is created. Thus, these fields cannot be edited and will be dimmed. If refine points are not defined, enter the number of rows and columns.

Editing 2D Grids

Each of the cells in a 2D grid can be active or inactive. An inactive cell is ignored when contours, fringes, or vectors are displayed on the mesh.

Each cell in the grid has an associated material type. When a new grid is created, the material type for each cell corresponds to the default material type. The default material type can be set using the Materials Editor command in the Edit menu. A new material can be assigned to a cell or a set of cells by selecting the cell(s) and then selecting the Properties command from the Edit menu.

Inserting Rows and Columns

Rows and columns can be added to an existing 2D grid by using the Add i Boundary tool and the Add j Boundary tool. Also, the interface between a row and a column can be moved by using the Move Boundary tool. (See 2D Grid Tool Palette)

Merging Rows and Columns

Rows or columns can be merged together by selecting the rows or columns using the Select i or Select j tools, right-clicking and selecting the Merge command from the pop-up menu. This command is the same as the Merge Cells command in the Grid menu in the main menu bar.