Generate Terrain command

Digital terrain surfaces can be used for the following tasks:

  • Extracting cross section geometry
  • Computing 2D flow areas
  • Determining bank locations
  • Assigning levees and lateral structures
  • Constructing roadway crossings
  • Defining dam structures
  • Extracting storage area volumes
  • Generating flood maps

While the software can read in a variety of terrain surface types, it is sometimes necessary to construct a terrain surface from newly acquired elevation data. This section describes how to do that.

  1. From the Map Edit ribbon menu, click the Generate Terrain dropdown combo box listing and then choose the Generate Terrain command.Generate Terrain command in GeoHECRAS
  2. The Generate Terrain dialog box will be displayed.

Generate Terrain Dialog Box

The following sections describe the Generate Terrain command and how to interact with the above dialog box.

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 be already 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:

  • CAD Drawing
  • GIS Data
  • LandXML Data
  • LIDAR Elevation Data
  • 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 using this command is a rectangular grid. The user can define the rectangular extents of the constructed terrain surface to an area of interest. The following options are available for defining the rectangular extents of the generated terrain surface:

  • Elevation source extents: The generated terrain surface grid will have the same extents as the original source data.
  • User-defined limits: The user can draw the rectangular extents of the generated terrain surface grid to limit to an area of interest. This will can possibly make the generated terrain surface file smaller and easier to work with. Click the [Pick] button to define the limits of the terrain surface. The dialog box will temporarily disappear and an information message will be displayed on the status line. Click and drag a rectangular region to define the limits of the generated terrain surface. 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 user-defined selected 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, cross sections, storage areas and 2D flow areas, plus an additional buffer boundary.

By default, the Crop terrain surface to TIN boundary option is checked if the user selects TIN surface or LandXML Data from the Terrain source entry. The generated terrain surface grid will not extend outside of the TIN boundary.

Terrain Grid Specifications

This section is used to define the specifications for the generated terrain surface.

Click the […] button for the Terrain file entry to specify the file name and directory location to save the generated terrain grid file.

By default, the Load terrain as map layer checkbox option is checked to load the terrain file as a layer in the Map Data Layers panel. Click the pencil icon to rename the layer.

The user can select the CRS to be used for the terrain grid. If there is only one CRS in the project, the software automatically selects it.

By default, the Overwriting existing terrain layer checkbox option is checked. This option controls overwriting an existing terrain layer with the same layer name.

Terrain Grid Resolution

This section is used to define the terrain quality and the cell size for the terrain grid being generated.

From the Predefined terrain quality entry, choose the resolution option to be used. Elevation grid resolutions range from low to ultra-high quality for the terrain surface grid being generated.

From the User-defined cell size entry, the user can manually define the elevation grid cell size. The finer the grid resolution (or smaller the cell size) defined, the greater the detail can be represented in the generated terrain surface.

After the options have been defined, click the [Generate] button and the software will create the elevation grid file and optionally load the grid as a new layer in the Map Data Layers panel.

About the Author Chris Maeder

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