Terrain surfaces can be used for the following tasks:
- Extracting cross section geometry
- Assigning levee elevations
- Generating flood maps
While the software can read in a variety of terrain surface types, it is sometimes necessary to construct a new terrain surface from raw elevation data. This section describes how to do that.
To generate a terrain elevation surface, select the GIS Edit | Generate Terrain command.
The software will display the Generate Terrain dialog box.
Need to recapture this dialog box when the user-defined cell size field is auto-computing the cell dimensions based upon the user’s terrain quality selection.
The following sections are contained within the dialog box.
Map Layer Details
This section defines the layer name to be created in the Map Data Layers panel for the generated elevation terrain surface.
Terrain Elevation Source
This section controls the selection of the elevation data source to be used for generating the terrain surface. If a map data layer was selected prior to selecting this command, the map data layer will already be selected within this section.
From the Terrain source entry, select the terrain source type to be used for generating the terrain surface. The following terrain source types are supported:
- AutoCAD Drawing
- GIS Contours
- GIS Points
- Point Elevation Data
- TIN Surface
Based upon the terrain source type selected, additional fields are provided for selecting the map data layer and attribute information.
Terrain Grid Limits
The terrain surface that is constructed from the Generate Terrain command is a rectangular grid. The grid location and size are controlled by this section. The grid location and size can be specified by the following options:
- Elevation source limits
The generated terrain surface grid will be the same size as the original source data.
- User-defined limits
The user can define the location and size of the generated terrain surface grid. Click on the [Define] button to define the limits of the terrain surface. The dialog box will temporarily disappear and a status line information message will be displayed to the user. Click and drag a rectangular region for extracting terrain elevation data. After releasing the mouse, the user will be returned to the dialog box. A layer will be created with a rectangular box to represent the selected user-defined region.
- HEC-RAS model extents
If a HEC-RAS model has been defined, this option will create a bounding rectangular region the same size as the HEC-RAS model reaches and cross sections, plus an additional buffer boundary.
Terrain Grid Resolution
This section is used to define cell size for the terrain surface grid to be generated. The user can either select from predefined grid resolutions or can manually define the grid cell size. The finer the grid resolution (or smaller the cell size) selected, the greater detail can be represented in the generated terrain surface.