Extract Cross Section Geometry Command (GeoSTORM)

The Extract Cross Section Geometry command allows the user to extract the cross section geometry from an underlying elevation grid where valid elevation data are present. The software will automatically recognize the limits of the elevation data and extract the cross section geometry for that data. It will not try to extract cross section geometry data where valid elevation data are not present.

For example, the underlying elevation grid might be of the river channel only. Previously, extracting the cross section geometry for this area required that the user define the channel bank stations at the limits of the elevation data and then extract the cross section geometry only for the cross section channel. If the user tried to extract the cross section geometry for the overbank areas, the overbank geometry would be flat.

Follow the steps below to use the Extract Cross Section Geometry command:

1. From the Input ribbon menu, click the Cross Sections dropdown menu and select the Extract Cross Section Geometry command.
   
2. The Extract Cross Section Geometry dialog box will be displayed.
   

The following sections describe how to use the Extract Cross Section Geometry command and interact with the above dialog box.

Selecting Cross Sections

The Select Cross Sections section is used to manually select single or multiple cross section(s) to extract geometry. This section includes a table listing all cross section(s) in the current scenario of the project, as shown below.

The user can select the cross section(s) using any of the following methods for extracting geometry:

• Check the checkboxes corresponding to each cross section in the Select Cross Sections section.
• Click the [Pick] button, the Extract Cross Section Geometry dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user to select the cross section(s) from the Map View. Either select cross sections one by one or click on the reach and all associated cross sections will be selected from the Map View. After selecting the cross section(s), press the [Enter] key or right-click and choose Done from the displayed context menu. The Extract Cross Section Geometry dialog box will be redisplayed.
• Alternatively, press and hold down the [Ctrl] key while selecting the cross section(s) directly from the Map View. When finished, open the Extract Cross Section Geometry dialog box, and the selected cross section(s) will be shown as selected/checked within the Select Cross Sections section.

After selecting the cross section(s), the total number of selected cross section(s) will be displayed in the Total selected read-only field, as shown below.

Other Specifications

The Other Specifications section is used to define additional specifications for extracting cross section geometry, including elevation data sources, extraction limits, roughness values, and bank station assignments. The following panels are available in this section:

• Extraction Data
• Other Data
• Roughness

Extraction Data

The Extraction Data panel is used to define the data extraction specifications for the selected cross sections.

Extracting Elevation Data

The Extract Elevation Data subsection is used to define the elevation data source(s) to be used for extracting the cross section geometry. Depending on the terrain elevation source selected, the content of this subsection changes to specify additional elevation data information. Refer to this article in our knowledge base for information on the types of terrain elevation data that can be used for extracting cross sections.

The following options are available in the Terrain elevation source dropdown combo box:

• CAD Drawing
• Elevation Grid
• GIS Contours
• LandXML Data
• Terrain Surface
• TIN Surface

CAD Drawing

If the user selects CAD Drawing as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following options are displayed when CAD Drawing is selected as the terrain elevation source:

• CAD drawing layer: This dropdown combo box allows the user to select the CAD drawing layer available in the project.
• Drawing layers: Clicking the [Define] button adjacent to the Drawing layers entry displays the CAD Drawing Layers dialog box, allowing the user to define the properties of the drawing layers, as shown below.
  

Elevation Grid

If the user selects Elevation Grid as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following option is displayed when the Elevation Grid is selected as the terrain elevation source:

• Elevation grid layer: This dropdown combo box allows the user to select the elevation grid layer available in the project.

GIS Contours

If the user selects GIS Contours as the terrain elevation source, the contents of the Extract Elevation Data subsection changes, as shown below.

The following options are displayed when GIS Contours is selected as the terrain elevation source:

• GIS polyline layer: This dropdown combo box allows the user to select the GIS polyline layer type.
• Elevation attribute: This dropdown combo box allows the user to select the elevation attribute type.

LandXML Data

If the user selects LandXML Data as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following options are displayed when the LandXML Data is selected as the terrain elevation source:

• TIN surface layer: This dropdown combo box allows the user to select the TIN surface layer type.
• TIN surface: This dropdown combo box allows the user to select the TIN surface type.

Terrain Surface

If the user selects Terrain Surface as the terrain elevation source, the contents of the Extract Elevation Data subsection changes, as shown below.

The following option is displayed when the Terrain Surface is selected as the terrain elevation source:

• Terrain surface layer: This dropdown combo box allows the user to select the terrain surface layer type.

TIN Surface

If the user selects TIN Surface as the terrain elevation source, the contents of the Extract Elevation Data subsection changes, as shown below.

The following options are displayed when the TIN Surface is selected as the terrain elevation source:

• TIN surface layer: This dropdown combo box allows the user to select the TIN surface layer type.
• TIN surface: This dropdown combo box allows the user to select the TIN surface type.

Cross Section Geometry Extraction Control

The Cross Section Geometry Extraction Control subsection is used to control the amount of cross section geometry data to be extracted from the terrain model for the selected cross section polylines. These controls provide additional intelligence on whether to extend or limit the cross section cutting, based upon whether specific criteria have been met. This ensures that adequately deep cross sections are created on both sides of the river reach. The software will try to compute the cross section geometry data up to the specified depth and within the maximum cross section width defined in this subsection. Note that the checkbox at the Cross Section Geometry Extraction Control subsection should be checked to enable the content of this subsection. Otherwise, the content of this subsection is disabled (i.e., grayed out).

If the selected polylines do not extend outward far enough to get the cross section depth specified, the software will automatically extend the cross sections further outward. Similarly, if the selected polylines extend too far outward for the cross section depth specified, the software will automatically trim the cross sections.

Cross Section Extraction Options

The Cross Section Extraction Options subsection is used to control which portions of the cross section(s) are to be extracted.

For example, the user may have survey data for the cross section channel and a LIDAR digital terrain surface for the overbank areas. In this example, the user would only want to extract the cross section geometry for the overbank areas since the surveyed channel geometry is already accurate.

The Extract cross section geometry for dropdown combo box entry contains the following options:

• Both Overbanks
• Channel Only
• Entire Cross Section (default)
• Left Overbank Only
• Right Overbank Only
  

The Retain existing cross section geometry checkbox option is used to retain the geometry of the cross sections that were extracted previously using the CAD file. By default, this checkbox is unchecked.

Other Data

The Other Data panel allows the user to assign bank stations for the cross sections using channel width, channel depth, or bank polylines/polygons. The checkbox at the Assign Bank Stations subsection should be checked to enable the content of this panel. Otherwise, the content of this panel is disabled (i.e., grayed out).

Assign Bank Stations

The Assign Bank Stations subsection is used to extract channel bank locations based on the selected option.

The following options are available in this subsection:

• Define by channel width
  This radio button option is used to assign the bank stations using a defined channel width. The software first identifies the thalweg location on the cross section, then extends outward from the thalweg symmetrically until the required channel width is achieved. Clicking the […] button allows the user to measure the channel width from the Map View.
• Define by channel depth
  This radio button option is used to assign the bank stations using an assumed normal flow depth and a maximum channel width search distance. The software first identifies the thalweg location on the cross section, then extends outward from the thalweg until the required channel depth is reached while staying within the specified maximum channel width. Clicking the […] button allows the user to measure the maximum channel width from the Map View.
• Define by bank polylines/polygons
  This radio button option is used to assign the bank stations using selected polylines or polygons. Using the corresponding [Pick] buttons, the user can interactively select individual polylines or polygons on the Map View to be associated as bank stations. The user can click the [Clear] button to cancel the previous selection and redo the entire process. The software first identifies the thalweg location on the cross section, then extends outward from the thalweg until it reaches a previously selected bank polyline or polygon edge.

Assigning Manning’s Roughness and Flow Lengths

During the extraction of the cross section geometry, the software will automatically assign a default Manning’s roughness for the left overbank, channel, and right overbank areas. However, the user can adjust these Manning’s roughness values in the Roughness panel, as shown below.

Note that, while defining the Manning’s n values, the user can click the […] lookup buttons adjacent to these Manning’s roughness entry fields to display the Manning’s Roughness dialog box. This dialog box provides a reference to Manning’s roughness coefficients for some commonly used surface materials.

Extracting Cross Section Geometry

When all the options have been defined in the Extract Cross Section Geometry dialog box, click the [OK] button. The software will then extract the cross section geometry from the elevation terrain.