SMS:Converting Feature Objects

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Feature objects can be converted to other data types in SMS such as meshes, grids, scatter sets and cross sections. This can be accomplished by either right-clicking on a coverage in the project explorer and selecting a convert command or by selecting the following commands from the Feature Objects menu:

Extract Cross Section

The Extract Cross-sections command uses the cross section arcs and a digital terrain model (TINs are the only source that can currently be used) to extract the elevations at vertices of the feature arc cross-sections, or at the intersection points with the triangles.

Cross-sections for individual arcs may be extracted by selecting the arc(s) before choosing the Extract Cross-sections command. If not cross-sections are selected then the Use All Cross-sections option is used.

Point properties (thalweg, left bank, right bank) can be defined from a 1D-Hydraulic Centerline coverage, or by AutoMark. The AutoMark option will examine the elevations of the extracted cross sections and try to infer the thalweg (low point) and the left and right bank points (change of slope) automatically.

Line properties can be determined from an area property coverage by intersecting the cross-section arcs with the area property polygons and marking them in the cross section database.

Cross Section Database

When extracting the cross sections you will be prompted for the name of a cross-section database file. SMS stores all of the cross-section information in a text database file. The cross section database can also be edited independently using the Cross Section Editor tools. Extracting cross sections with feature arcs is only way to generate cross-section information, they also can be imported from spreadsheet files (cut and paste), or entered manually.

Map → 2D Mesh

Once a set of feature objects has been created for a coverage (conceptual model) associated with a finite element based model such as RMA2, FESWMS, ADCIRC or CGWAVE , the Map → 2D Mesh command can be used to generate a 2D finite element mesh from the objects. The Map → 2D Mesh command creates a 2D Mesh on the interior of all of the polygons in the current coverage. The figure domain of a flood plain using the feature objects in the Map Module. The second figure shows a 2D Mesh created from the polygons.

File:Flood plain domain.gif

Flood Plain Domain

File:Map to 2D mesh.gif

2D Mesh created from Map Objects using Map → 2D Mesh command

The recommended method for creating unstructured grids (meshes) in SMS for use with either finite element or finite volume engines is to use the conceptual modeling approach. This method includes the following general steps:

1. Define a bathymetric source (scatter set or raster/DEM).
2. Define a map module coverage consisting of polygons that cover the modeling domain. This is the region to be covered by the mesh.
3. Assign attributes to the points/arcs/polygons in the coverage to control the mesh characteristics.
   • Point meshing attributes:
     • Used to force the creation of a mesh node at a specific location.
     • Used to specify the element density in the area of the point location by assigning refine point attributes.
   • Arc meshing attributes:
     • Used to define linear features such as a river thalweg or an embankment toe/shoulder. Mesh nodes will be created along the arc.
     • Used to control element density if a size function (scalar paving) is not utilized. Vector spacing on the arc controls mesh node spacing for all mesh generation options except scalar paving.
   • Polygon meshing attributes:
     • Specify a bathymetry source for each polygon
     • Specify a meshing type for each polygon. Choose from:
       • Patching – create quad dominant elements conforming to a topographic rectangle.
       • Paving – create triangular elements layer by layer from the polygon boundary inward.
       • Scalar Paving – create triangular elements as with paving with the spacing controlled by a size function defined on an associated scatter set
4. Optionally, define an area property coverage to define the source of material attributes.
5. Issue the Map → 2D Mesh command is used to create a 2D mesh using the feature objects in a 2D Mesh Coverage. When the Map → 2D Mesh command is selected, the 2D Mesh Options dialog opens.

Map → 2D Grid

The Map → 2D Grid command is used to create 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. A grid frame must have 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 and the user can 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.

Grid Frame Properties

The grid frame properties dialog allows the user to specify the attributes applied to the grid frame when performing a "Map → 2D Grid" operation. These properties are as follows:

• Origin
• Orientation
• Directional properties (u and v direction)
  • Define cell sizes – specified uniform cell sizes
    • Cell size – the cell size in the specified direction
    • Number of cells – number of cells in the specified direction
  • Use refine points – refine points will be used to generate the grid
    • Maximum cell size – the max size the should exists when growing
    • Maximum bias – the max growth ratio to be used when growing
    • Use inner growth – specifies whether the cell sizes should grow between two refine points
  • Grid size – the grid dimension in the specified direction

When the user specifies "Define cell sizes", there are a few options available. These options are:

1. Specify cell size – specify the cell size and the number of cells will be computed.
2. Specify number of cells – specify the number of cells and the cell size will be computed.

If the grid is to have square cells, the v direction cell size will always be linked to the u direction cell size.

Refine Points

Refine points for a Cartesian Grid allow a user to change the cell dimensions when generating the grid. They are not available for all models, since some Cartesian Grid models require uniform cell sizes. The user can specify whether to refine in the I and/or J direction and the base cell size for each direction.

When the refining is performed, the base size may be changed in order to fit the other restrictions applied to the refining process. If two refine points are too close to each other to allow the cell size to transition, one will be ignored when generating the grid. See Refine Point Dialog for more information.

Depth and Vector Options

In addition to the options specified on the grid frame, depth and vector interpolation options can be specified during the mapping process for some models. The depth mapping is required for all models, while the vector mapping is optional even for the models it can be performed on. Depth and vector data sets can be constant or interpolated from a scatter set.

Cells a user specified tolerance above the datum can be marked as land (inactive) cells. This option is on by default for BOUSS-2D, but defaults to off for other models.

When specifying a constant vector, the X and Y components are oriented based on global space, not grid space.

The name of the vector dataset can be specified, but the name of the depth dataset is always set to "Depth".

Map → 2D Scatter Points

The Map → 2D Scatter Points command creates a scatter point set from the points and nodes and vertices of the current coverage. The process is different for observation coverages and non-observation coverages.

• Non-observation Coverages

With non-observation coverages, a single elevation data set is created for the 2D scatter points representing the Z location of all the points, nodes and vertices.

• Observation Coverages

With observation coverages, the Observation Points → Scatter Points dialog appears. This dialog allows you to create a data set for the 2D scatter points from one of the measurements associated with the observation points.

Measurement

A dataset is created for the 2D scatter points from the measurement selected in the dialog. The model associated with the selected measurement (if any) is shown, along with whether the measurement is steady state or transient.

Time Step Times

This section of the dialog is only available if the selected measurement is transient. It allows you to define the number of timesteps, and the timestep times to be created for the scatter point dataset.

• Match all unique times

  The Match all unique times option gets the set of unique times from the XY series of all the observation points. This is the union of all the times. If some XY series use dates/times and others don’t, this option won’t be available. Otherwise, the times in the spreadsheet will be displayed as either dates/times or relative times depending on the XY series. The spreadsheet will not be editable. The Use dates/times toggle will be unavailable but set according to whether the observation point XY series use dates/times or not. The Reference time section will be unavailable, but if the XY series use dates/times, the minimum time will be used as the reference time for the scatter point dataset.

• Match time steps from model

  The Match time steps from model option will only be available if the measurement is associated with a model, and the model is transient. If so, this will be the default choice and GMS will get the times to display in the spreadsheet from the stress period and time step info for the model. The spreadsheet will not be editable. The Use dates/times toggle will be unavailable but set according to whether the model uses dates/times or not. The Reference time section will be unavailable, but if the model uses dates/times, the model reference time will be used as the reference time.

• Specify times

  The spreadsheet of times will be editable with this option and you can copy and paste times from another program such as a spreasheet. Also, the Initialize Times button becomes available allowing you to bring up a dialog you can use to create times at a specified interval. If you select the Use dates/times toggle, the Reference time section will become available and the times in the spreadsheets will be displayed as dates/times.