SMS:Cartesian Grid Module Overview

Cartesian grid module

Overview

The 2D Cartesian Grid Module contains tools used to construct 2D Cartesian finite difference grids. These grids consist of cells aligned with a rectilinear coordinate system.

Some models limit the grid to be defined with square cells, others limit to constant sized rectangular cells, while others add the flexibility of having variable sizes to the cells (variable row height or column width. It is used to create, edit, and visualize rectilinear grids. Datasets can have values at cells, corners, and midsides.

Functionalities

The 2D Cartesian Grid Module contains tools used to construct 2D Cartesian finite difference grids. These grids consist of cells aligned with a rectilinear coordinate system.

Some models limit the grid to be defined with square cells, others limit to constant sized rectangular cells, while others add the flexibility of having variable sizes to the cells (variable row height or column width.

It is strongly recommended that grids be created through the Map Module. The grid module currently includes interfaces for:

• BOUSS-2D – phase resolving Boussinesq wave energy and circulation model
• CMS-Flow – hydrodynamic circulation specifically adapted for coastal zone
• CMS-Wave – wave energy model
• STWAVE – wave energy model
• TUFLOW – Coastal, Riverine, and Urban hydrodynamic model with emphasis in flooding applications

Grid Types

Types of 2D Grids Supported by models SMS. (a) Mesh-Centered Grid (b) Cell-Centered Grid. In Cartesian grids, row and column boundaries are straight. Each cell center or grid node can have a unique elevation. The grid can also be rotated about the Z axis if desired.

File:GridType1.bmp

Types of 2D Grids Supported by SMS models: (a) Mesh-Centered Grid, (b) Cell-Centered Grid.

Creating and Editing 2D Grids

Create Grid. A new grid can be created by selecting the Create Grid tool from the Cartesian Grid Tools. With this tool active, the user can create a grid by clicking on three points in the graphics window. The first click defines the origin of the grid, the second click defines the orientation of the grid and length of the I axis and the third click defines the length of the length of the J axis. Once the user clicks three times defining the three points, the Map → 2D dialog appears.

Editing 2D Grids. Each of the cells in a 2D grid can be active (water) or inactive (land). An inactive cell is ignored when contours or vectors are displayed on the grid and by the numeric engine during computation. If a cell has the potential of becoming active (due to wetting/drying or a similar process), it should be classified as active. Cells status is specified by selecting the cell and assigning a status through the model menu.

Rows and columns can be added to an existing grid that supports variable row/column size by using the Insert Row, Insert Column, Drag Row, or Drag Column tool. (See 2D Grid Tool Palette)

Smoothing 2D Grids

It may be useful to smooth the spatial data stored on a 2D grid for a number of reasons. These reasons include:

• In order to conserve the amount of disk spaced required to store a DEM, many DEM formats store elevations rounded to the nearest integer value. This causes elevation changes to occur in discrete steps rather than smoothly, as would be the case in nature. In regions of low relief, rounded elevations can cause an area to be artificially "flat."
• Surveys may include anomalies. Smoothing algorithms blend these bad data points into the surrounding values.
• Datasets may include spurious noise either from physical conditions such as waves or numerical filtering. Smoothing can dampen these variations.

When you right-click on the grid in the Project Explorer, operations for the grid appear in a pop up window. One of these is the smooth operation.

Converting 2D Grids

2D Grids may be converted to other types of data used in SMS, such as a Scattered dataset of 2D mesh. 2D Grids can be converted by right-clicking on the grid in the Project Explorer.

Project Explorer

Cartesian Grid Module Root Folder Right-Click Menus

Right-clicking on the Cartesian Grid module root folder in the project explorer invokes an options menu with the following options:

• Display Options

Cartesian Grid Item Right-Click Menus

Right-clicking on a Cartesian Grid item in the Project Explorer invokes an options menu with the following module specific options:

• Smooth – Opens the Cartesian Grid Smoothing Options Dialog.

Model Specific Right-Click Menus

Command	Description	Applicable Models
Create Transformed Grid	Opens the Create Transformed Grid dialog. Creates a copy of the grid with a rotated origin. Used to change the I direction for wave models.	CMS-Wave, STWAVE

Menus

The Cartesian Grid Module Data Menu commands include:

Model Specific Menus

• BOUSS-2D
• CMS-Flow
• CMS-Wave
• STWAVE
• TUFLOW

Model Commands

• Steering Module
• Switch Current Model

Dataset Commands

• Data Calculator
• Dataset Toolbox
• Create Datasets
• Map Elevation
• Zonal Classification

Visualization Commands / Options

• Contour Options
• Vector Options
• Film Loop

Data Conversion Commands

• Grid → Scatterpoint
• Grid → Map
• Grid → Mesh

Grid Commands

• Find Cell

How do I?

To learn more about how to use the Cartesian Grid Module go to the Tutorials section.

Cartesian Grid Tools

The following tools are contained in the Dynamic Tools portion of the tool palette when the Cartesian Grid module is active. Tools specific to a model interface are described with the corresponding model. Only one tool is active at any given time. The action that takes place when the user clicks in the Graphics Window depends on the current tool. The following table describes the tools in the Cartesian Grid module tool palette. Depending on the current model, and the type of grids it supports, some of these tools may not be available.

Tool	Tool Name	Description	Right-Click Menu
File:SMS CGrid Select Cell Tool Icon.bmp	Select Cell	The Select Cell tool is used to select a grid cell. A single cell is selected by clicking on it. A second cell can be added to the selection list by holding the SHIFT key while selecting it. Multiple cells can be selected at once by dragging a box around them. A selected cell can be unselected by holding the SHIFT key as it is clicked. When a single cell is selected, its Z coordinate is shown in the Edit Window. The Z coordinates can be changed by typing in the edit field, which updates the depth function. If multiple cells are selected, the Z Coordinate field in the Edit Window shows the average depth of all selected cells. If this value is changed, the new value will be assigned to all selected points. With one cell selected, the Edit Window shows the point i,j location. With multiple cells selected, the Edit Window shows the number of selected cells. The number and size of the cells can be changed in the Model Control.	When one or more Cartesian grid cells are selected, and there is a scatter set in the project, a right-click in the graphic window will bring up a menu. One of the options is Interpolate Bathymetry.... This option brings up the Interpolation dialog where the desired source scatter dataset can be selected. When OK is clicked, SMS will interpolate the selected cell(s)' elevations based on the chosen scatter dataset.
File:SMS CGrid Select Row Tool Icon.bmp	Select Row	The Select Row tool is used to select cell rows. Rows are selected in the same manner as selecting individual cells.	N/A
File:SMS CGrid Select Column Tool Icon.bmp	Select Column	The Select Column tool is used to select cell columns. Columns are selected in the same manner as selecting individual cells.	N/A
File:SMS CGrid Split Grid Column Tool Icon.bmp	Split Grid Column	Insert a new column into an existing grid. This tool splits an existing column into two columns at the location selected by the user.	N/A
File:SMS CGrid Split Grid Row Tool Icon.bmp	Split Grid Row	Insert a new row into an existing grid. This tool splits an existing row into two rows at the location selected by the user.	N/A
File:SMS CGrid Drag Column Boundary Tool Icon.bmp	Drag Column Boundary	Edit column boundary. This tool makes one column narrower while making its neighbor wider.	N/A
File:SMS CGrid Drag Row Boundary Tool Icon.bmp	Drag Row Boundary	Edit row boundary. This tool makes one row taller while making its neighbor shorter.	N/A
File:SMS CGrid Select Cell String Tool Icon.bmp	Select Cell String	Select a “Cell String”. Allows assignment of boundary conditions.	N/A
File:SMS CGrid Select Cell String Tool Icon.bmp	Create Cell String	Create a “Cell String”. This tools allows the user to define a string of cells for later assignment of boundary conditions or flux observations.	N/A

Related Coverages

The grid module currently includes interfaces for:

• BOUSS-2D – phase resolving Boussinesq wave energy and circulation model
• CMS-Flow – hydrodynamic circulation specifically adapted for coastal zone
• CMS-Wave – wave energy model
• STWAVE – wave energy model
• TUFLOW – Coastal, Riverine, and Urban hydrodynamic model with emphasis in flooding applications