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Georeference Junctions Command

When defining a reach, the user might use multiple cross sections or reach geometries to define each reach. In this situation, several reaches are connected with junctions to represent the extent of the reach in which the defined cross section or reach geometry should be applied. If a junction is not located at the correct location on the river reach, the user can use the Georeference Junctions command to automatically map that junction to a desired location.

The Georeference Junctions command provides three options for mapping junctions to the desired locations, as listed below:
  • Snap to Alignment Point
  • Slide along Alignment Polyline
  • Draw on Map View

Follow the steps below to use the Georeference Junctions command:

  1. From the Input ribbon menu, expand the Routing Junctions menu item and select the Georeference Junctions command.
    Georeference Junctions Command
  2. The Georeference Junctions dialog box will be displayed.
    Georeference Junctions dialog box

The following sections describe how to georeference a junction to a desired location and to interact with the above dialog box.

Selecting Junction to Georeference

The Select Junction to Georeference section allows the user to select the junction that is to be georeferenced. The user can select the junction from the Junction ID dropdown combo box listing all the junctions contained within the model. Alternatively, the user can click the [Pick] button to select the junction from the Map View.

After clicking the [Pick] button, the Georeference Junctions dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user what to do next. The user can then interactively select a junction from the Map View.

Note that the user can select only one junction at a time to georeference.

Upon selecting a junction, the user is immediately returned to the dialog box, and the selected junction is highlighted on the Map View.

Note that the Junction ID dropdown combo box updates automatically to match the selected junction.

Snapping Junction to an Alignment Point

If an existing alignment point for the junction exists on the Map View, the Snap to Alignment Point option can be used to snap the HEC-HMS junction to the alignment point so that the HEC-HMS junction matches that of the alignment point.
Snap to Alignment Point option

The user can click the [Pick] button to select the alignment point from the Map View. On clicking the [Pick] button, the Georeference Junctions dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user on what to do next. The user can then interactively select the alignment point from the Map View.

Upon selecting the point, the user is immediately returned to the dialog box, and the status of Select alignment point read-only field changes to Selected. The user can select only one alignment point to use for georeferencing.

Once the junction alignment point is selected, the user can click the [Snap] button. On clicking the [Snap] button, the software will snap the selected junction to the selected alignment point.

Sliding Junction along an Alignment Polyline

If a HEC-HMS junction has been snapped to an alignment point (on the defined reach) on the Map View but is not precisely located where it should be, the Slide along Alignment Polyline option can be used to slide the junction along the defined river reach.
Slide along Alignment Polyline option

On selecting the Slide along Alignment Polyline radio button option, the [Slide] button becomes enabled (no longer grayed out). On clicking the [Slide] button, the Georeference Junctions dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user on what to do next.

The user can then “slide” the junction along the defined river reach on the Map View. However, the command doesn’t allow sliding when an adjacent cross section is encountered.
Georeference junction slide functionality

Once finished, the user can press the [Enter] key or right-click and select Done from the displayed context menu. The dialog box will be redisplayed, and the junction will be placed at the new location.

If the user slides the junction along a reach, and the project is in a projected CRS, then Recompute adjacent reach lengths checkbox option can be used to recompute the adjacent reach lengths. By default, this checkbox is checked.

Note that the user cannot use the “slide” functionality to change the location of the termination (upstream most or downstream most) junctions on multiple reaches.

Drawing Junction Node on Map View

The Draw on Map View radio button option allows the user to draw a junction node on the Map View to which the selected junction is to be georeferenced.
Draw on Map View option

On selecting the Draw on Map View radio button option, the [Draw] button becomes enabled (no longer grayed out). The user can click the [Draw] button to interactively draw the junction node on the Map View.

On clicking the [Draw] button, the Georeference Junctions dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user on what to do next. The user can then draw the junction node on the Map View. Once finished, the user can press the [Enter] key or right-click and choose Done from the displayed context menu. The dialog box will be redisplayed, and the selected junction will be georeferenced to the drawn node.

Assigning Junction Elevation

The Assign Junction Elevation section uses the elevation data to assign an invert elevation to the georeferenced junction. The user should define the data for this section before georeferencing junctions. Alternatively, the user can use the Assign Junction Elevations command to assign invert elevations to the already drawn junctions. Refer to this article in our knowledge base to learn more about this command.

For assigning elevation data, this section only supports the following surface types:
  • Elevation grids
  • LandXML data
  • TIN surfaces
It does not support the following surface types:
  • CAD drawings
  • GIS contours

The user can also apply an elevation offset to raise or lower the selected junction by the specified amount by checking the Apply elevation offset checkbox. On selecting this checkbox, the entry field next to it becomes available for entering an elevation offset value. For example, the user can define a negative offset value to lower the junction for specific circumstances, such as representing a manhole bottom elevation.

About the Author Chris Maeder

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