Georeference Cross Sections Command (HEC-HMS)

When the GeoHECHMS software imports a model, it automatically places the cross sections on the Map View. However, if the original model was not spatially georeferenced, the cross sections will not align with any loaded background base map. While the software can operate without any issues in this situation, it is preferable to have the cross sections georeferenced to the background base map. Therefore, it might become necessary to georeference the imported cross sections.

The Georeference Cross Sections command of the GeoHECHMS software can be used to manually georeference each of the cross sections to the background base map displayed in the Map View. The process of georeferencing a cross section to the Map View can be a trial and error process—especially when the exact location of the original cross section is not known. Using the Georeference Cross Sections command, this process is accelerated.

Note that a CRS should be assigned prior to running this command. Otherwise, the software will display the below informational dialog box.

Refer to this article in our knowledge base to learn how to assign a coordinate reference system to a project.

Follow the steps below to georeference an existing cross section in GeoHECHMS:

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

The following sections describe how to georeference an existing cross section and interact with the above dialog box.

Selecting Cross Section to Georeference

The Select Cross Section to Georeference section allows the user to interactively select the cross section to georeference on the Map View. The user can either select the cross section from the Cross Section ID dropdown combo box or click the [Pick] button to select the cross section from the Map View. Once the cross section is selected, the reach associated with the selected cross section will be displayed in Reach ID read-only field.

Note that the user can click the [Clear] button to cancel the previous selection and redo the entire process.

Once the cross section has been selected, the user can choose between the following options to georeference the cross section:

Snap to Alignment Polyline

If an existing alignment polyline for the cross section exists on the Map View, the Snap to Alignment Polyline option can be used to snap the cross section to the alignment polyline.

Follow the steps below to use the Snap to Alignment Polyline option:

1. Select the Snap to Alignment Polyline radio button option.
2. Click the [Pick] button.
   
3. The Georeference Cross Sections dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user to select the alignment polyline.
4. Select the alignment polyline on the Map View.
5. The Georeference Cross Sections dialog box will be redisplayed and the status of the Select alignment polyline read-only field will change from Not Selected to Selected. Click the [Clear] button to cancel the previous selection and redo the entire process.
6. Then, click the [Snap] button to snap the selected cross section to the alignment polyline. The user can turn on the Scale to fit checkbox option to scale the cross section to fit within the alignment polyline.
   

Note that if the selected cross section polyline does not overlay the previously defined reach, the following informational dialog box will be displayed.

Slide Along Alignment Polyline

This option allows the user to manually slide the cross section along the alignment polyline.

Follow the steps below to use the Slide along Alignment Polyline option:

1. Select the Slide along Alignment Polyline radio button option.
2. Click the [Pick] button to select the alignment polyline from the Map View.
   
3. Selecting the alignment polyline from the Map View displays the following informational dialog box. Click the [Yes] button to select the polyline or abort the selection by clicking the [No] button.
   
4. Once the alignment polyline is selected, click the [Slide] button.
   
5. The Georeference Cross Sections dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user to select the cross section and drag it along the underlying alignment polyline.
   Note that if the cross section does not overlay an alignment polyline, the following informational dialog box will be displayed.
   
6. Click and drag the cross section on the Map View to revise its alignment.
7. When finished, press the [Enter] key or right-click and select Done from the displayed context menu. The Georeference Cross Sections dialog box will be redisplayed.
8. The user can also check the Recompute adjacent node element elevations checkbox option to recompute the elevation of the adjacent node type elements after georeferencing the cross section.

Note: For more precision, the user can use the Snap to Alignment Polyline option first and then use the Slide along Alignment Polyline option.

Draw on Map View

This option allows the user to draw an alignment polyline and automatically snap the selected cross section to the drawn polyline.

Follow the steps below to use the Draw on Map View option:

1. Select the Draw on Map View radio button option and click the [Draw] button.
   
2. The Georeference Cross Sections dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user to draw the alignment polyline on the Map View.
3. Draw the alignment polyline on the Map View. When finished, press the [Enter] key or right-click and select Done from the displayed context menu.
4. The Georeference Cross Sections dialog box will be redisplayed, and the cross section will automatically snap to the drawn alignment polyline.

Extract Elevation Data

This optional section is used to define the elevation data source to be used for extracting the cross section geometry. Depending upon the elevation data source type that is selected, different options are provided 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 constructing cross sections.

Note that if the Extract Elevation Data checkbox is unchecked, then the options under the subsequent sections will be unavailable (i.e., grayed out).

Cross Section Geometry Extraction Control

This optional section is used to control the amount of cross section geometry to extract for the drawn cross section polylines. This assures that an adequately deep enough cross section is created on both sides of the reach. The software will attempt to retrieve the cross section geometry data to the depth specified within the specified maximum cross section width.

If the drawn polyline does not extend outward far enough to get the cross section depth specified, the software will automatically extend the constructed cross section further outward. Similarly, if the drawn polyline extends too far outward for the depth specified, the software will automatically trim the constructed cross section.

Cross Section Extraction Options

This section is used to control which portions of the cross section(s) should 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 contains the following entries: