The Data menu provides options for bathymetry interpolation as well as accessing online bathymetry data. Being able to view bathymetry underneath the grid helps determine the resolution required in the deep and main channel regions compared to shallow regions, which can often have lower resolutions. The Grid Bathymetry Interpolation and Download Online Bathymetry options are shown in Figure 1 and their use is described below.
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The grid is displayed as shown in Figure 17. We can see that only some grid cells in two head ends of the grid cover the cross sections. We should interpolate for those cell's bathymetry first.Draw
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Figure 16 Cross-sections loaded and located in the river segment.
Anchor Figure 17 Figure 17
Figure 17 High-resolution grid covers the cross-sections.
Click Add a polyline button from the Main Toolbar to draw a polygon to cover the grid cells near the cross-sections, as shown in Figure 18. Then, change the cursor to select object mode (press the S key or select the Select Object in the main toolbar). Select the overlay layer (the layer that contains the new polygon), then LMC on the polygon to select it (it will be highlighted by changing color to red), then RMC to display options, and select the Interpolate Grid Elevations option as shown in Figure 19. A message will be shown as in Figure 20 when the interpolation process is complete. Click the OK button to close the message.
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Apply similar steps to interpolate the bottom elevation of grid cells near the second cross-section.
Anchor Figure 18 Figure 18
Figure 18 Draw two polygons covering grid cells and cross-section.
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Figure 19 Interpolate grid cells near the cross-section.
Anchor Figure 20 Figure 20
Figure 20 Grid Bathymetry Interpolation message.
To view the bottom elevation of cells that are interpolated, RMC on the grid layer and select Show Properties / Bottom Elevation as shown in Figure 21. Then the grid's bottom elevation will be displayed as shown in Figure 22.
Next, we will interpolate the bottom elevation for entire of the grid based on grid cells with the existing bottom elevation in two grid
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heads. Select the grid layer in the
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Control Panel and
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set the cursor
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in selection mode. Select the
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first grid node
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and hold the Shift key to select the second node
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(select two grid nodes to define the grid block we want to interpolate). In this case, we select two grid nodes to cover the entire grid. The grid block will be highlighted by changing the color to red
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, then RMC to display options
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and select the Interpolate Elevations in I Direction option as shown in Figure 23.
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After the interpolation process is done, the grid bottom elevation
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Figure 16 Cross-sections loaded and located in the river segment.
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Figure 17 High-resolution grid covers the cross-sections.
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Figure 18 Draw two polygons covering grid cells and cross-section.
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Figure 19 Interpolate grid cells near the cross-section.
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is displayed as Figure 24.
Anchor Figure 21 Figure 21
Figure 21 Show the grid bottom elevation of grid cells.
Anchor Figure 22 Figure 22
Figure 22 Grids with bottom elevation at two cross-sections.
Anchor Figure 23 Figure 23
Figure 23 Interpolate the grid block in I direction.
Anchor Figure 24 Figure 24
Figure 24 Grid with bottom elevation.
Besides the interpolation feature, Grid+ has a feature to replicate the grid elevation. For example, in an extrapolation feature. In this case, some upper grid cells cells in the two head ends of the grid are missing the data of bottom elevation. FirstlyTo fill in their bottom elevation, select the grid layer in the control panel Control Panel and change set the cursor to in selection mode. Select a grid node and hold the Shift key to select the second node, the block that covers both cells missing bottom elevation and cells having bottom elevation. The grid block will be highlighted by changing the color to red. Note that the number of grid cells having bottom elevation values should be similar to the cells missing data. Then RMC to the grid cells to display options , and select the Extend Elevations in I Direction option as shown in Figure 25. The bottom elevation values will be expanded extended to the upper cells . Figure 26 presents the grid bottom elevation after extensionthat are missing values. As a result, the bottom elevation for those cells is assigned as shown in Figure 26.
Anchor Figure 25 Figure 25
Figure 25 Extend elevation in I-direction.
Anchor Figure 26 Figure 26
Figure 26 Grid cells after extension bottom elevation.
Download Online Bathymetry
After selecting the Download Online Bathymetry option, the Download Online Data form will be displayed as shown in Figure 27. Users are able to select data set using the drop-down Data Set. The currently available open-source sites are:
- GEBCO 2021: This is 2021 GEBCO’s gridded bathymetric data set, the GEBCO_2021 Grid, is a global terrain model for ocean and land, providing elevation data, in meters, on a 15 arc-second interval grid. The data information can be found on GEBCO's website GEBCO 2021.
- GEBCO 2014: This is 2014 GEBCO’s gridded bathymetric data set. The data information can be found on GEBCO's website GEBCO 2014.
- GEBCO 08: a continuous terrain model for ocean and land with a spatial resolution of 30 arc-seconds released by the General Bathymetric Chart of the Oceans (GEBCO) in 2009. Bathymetric data is available to download, and the user manual can be found on the website GEBCO 08.
Depending on the data set selected, different data information is provided in the Spatial Information section. The Data Extraction Limits is auto-set to the whole model domain, but the user can manually select the specific area by checking to Using Polygon File and browser to the closed polygon that contains the area inside.
Click on Download button and Grid+ will download and apply the bathymetry data of the selected Data Set to the specific defined area.
Anchor Figure 27 Figure 27
Figure 27 Download online data for bathymetry.
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