Interpolation can be invoked explicitly or implicitly. The implicit invocation is part of the automatic mesh or grid generation. Explicit interpolation occurs when the user selects an Interp to ... option in the Scatter menu in the Scatter module. These commands require that at least one scatter point set exist with at least one function associated. A mesh or grid must also exist in order for the associated interpolation command to be available.
When the user selects either interpolation command, the interpolation option dialog appears labeled to indicate what interpolation is being performed. The user selects the appropriate options and once the OK button is selected, the interpolation procedure is performed. The options are:
New interpolated data set name - The name of the new data set (or function) created by interpolation.
Map Elevation - For interpolation to mesh nodes, the new data set is mapped to be the elevation function.
Interpolation Method - Since no interpolation scheme is superior in all cases, SMS supports three interpolation techniques. Many other methods are possible, however, since surface water modeling requires a fairly rich data set, the more simplistic interpolation methods are more applicable. The user selects a current method that is used for all interpolation until the user selects another method. The supported methods include:
Natural Neighbor (NN)
Default extrapolation value - If the scatter set does not bound the data being interpolated to, the extrapolation value is used (for Linear and NN interpolation only).
Truncate Values - When interpolating a set of values, it is sometimes useful to limit the interpolated values to a specific range. For example, when interpolating contaminant concentrations, a negative value of concentration is meaningless. However, many interpolation schemes will produce negative values even if all of the scatter points have positive data values. This occurs in areas where the trend in the data is toward a zero value. The interpolation may extend the trend beyond a zero value into the negative range. In such cases it is useful to limit the minimum interpolated value to zero. Interpolated values can be limited to a given range by entering a minimum and maximum interpolation value.
Scatter Set/Function - The user selects the desired scatter point set and the function to interpolate from.
Time Steps - The user selects the option to interpolate a single time step or multiple time steps (if the function is transient).
Time Step Interpolation - If interpolating multiple time steps, the user can select the beginning time, the step size, and the number of time steps to interpolate. The user can also choose to interpolate between time steps or to match time steps that fall within the specified time range.