Aquaveo & Water Resources Engineering News

Editing DEM Elevations

Do you have a Digital Elevation Model (DEM) that has elevations that need to be adjusted? Editing DEM elevations can sometimes prove difficult. However, with WMS you can edit the elevations of DEM files using several tools WMS provides for editing DEM elevations.

Here are a couple ways DEM elevations can be edited in WMS:

Editing Single Points

Some DEMs have a single point where the elevation is off. You can edit a single point in a DEM by using the Select DEM Points tool and selecting the point. You can then edit the point elevation by double-clicking on the point to bring up the DEM Point Attributes dialog where the elevation value can be changed.

Using Feature Arcs to Edit Elevation

Sometimes, the elevation of a DEM needs to be adjusted to follow a specific line, such as a river bed or proposed irrigation channel. The elevation in this location can be adjusted using a feature arc. This is done by selecting the feature arc then right-clicking and selecting the Edit DEM Elevations command.

Editing DEM Elevation using an Arc

In the Edit DEM Elevations dialog, you can change the elevation of the DEM along the arc. This can be done by selecting and changing elevation points on the arc in the profile window. For editing all of the elevation values along the arc, the dialog provides the following options:

  • You can offset all of the arc elevations by using the Offset elevations by a constant button.
  • You can set all of the elevation values to a constant by using the Set to constant elevation button.
  • Finally, you can use the Interpolate button to interpolate the values to between the first and last values on the arc. This will smooth out the elevation to create an artificial slope.

Using these tools makes adjusting the elevations of DEMs easier. Try them out in WMS today!

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Using the Temporal Tools in the Dataset Toolbox

SMS contains several ways to work with datasets. Perhaps the most useful of these is the Dataset Toolbox. The Dataset Toolbox has several tools for generating new datasets. Among these are the temporal tools which allow adjusting the time steps for a transient dataset. The temporal tools include two options: Sample Time Steps and Merge Dataset.

The Sample Time Steps tool allows the creation of a dataset with a different number of time steps. The time steps can either be increased or decreased. To use the Sample Time Steps tool:

  1. Open the Dataset Toolbox and select the Sample Time Steps tool.
  2. Select the transient dataset you want to use.
  3. Select the starting and end times.
  4. Enter the time step frequency and units.
  5. Give the new dataset a name and click Sample.
Dataset Toolbox showing the Sample Time Steps tool

The other temporal tool is the Merge Dataset tool. This allows us to combine two transient datasets. To use this tool, the transient datasets being combined cannot have overlapping time steps. Most often, this tool is used to append multiple simulation runs together.

For example, if you completed an SRH-2D model run for one day, then created a new simulation for a second day (using a hot start file from the end of the first day simulation run), you could combine the results of the two simulation runs using the Merge Dataset tool.

To use the Merge Dataset tool:

  1. Open the Dataset Toolbox and select the Merge Datasets tool.
  2. Select the first dataset to use, then select the second dataset.
  3. Enter a name for the combined dataset and click Compute.

When using the Merge Dataset tool, make certain that the first dataset selected has time steps that are earlier than the second dataset selected.

The temporal tools in the Dataset Toolbox provide a simple way to adjust transient datasets in your project. Try using these tools in SMS today!

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The HDF5 File Format and MODFLOW

The HDF5 file format is a cross platform binary format for storing scientific data. HDF5 allows you to reduce the size of the file data by compressing repeated values. This allows your data to be read and written much faster than if you stored the data as ASCII (plain text) files. GMS can read and write to HDF5 files, and stores its own HDF5 files with the other MODFLOW data files.

Exporting an HDF5 file

There are no hard file size limits. The number of objects within an HDF5 file is not limited, and the format supports complex relationships through grouping and linking. In addition to support for common metadata types, you can create user-defined metadata to accommodate whatever needs you have in your project. The only limits with these are the capabilities of your computer.

HDF5 was designed to be extensible and to allow for future changes to the platform. GMS takes advantage of this by checking HDF5 data for key values in order to substitute them into your arrays or lists. This allows you to better use transient parameters and very large pilot point sets. GMS handles the pilot point interpolation through an external routine that helps speed up the processing.

There are external HDF5 file viewers and editors, such as HDFView. However, it is very easy for you to modify the data in such a way that it makes the HDF5 unreadable by GMS. Because of this, we recommend only viewing the files using these tools. You should only manually edit the file if given explicit directions by a developer. If modifications need to be made to the HDF5 file, we recommend you make the changes to your project in GMS which will re-export the HDF5 file.

Learn more about the HDF5 file format from the HDF Group, a consortium of scientists worldwide that works on the HDF5 format. You can also read the article on the XMSWiki about using the HDF5 format with MODFLOW. This article goes into more details about multiple specific uses for the file format.

Make use of HDF5 files with MODFLOW in GMS today!

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