## Interpolation Methods

VS2DHI provides two interpolation methods to estimate values at
cell nodes from contours that specify the initial distribution
of pressure head, moisture content, and temperature.

To select an interpolation method for an initial condition, first
make sure that the initial condition is selected in the
"Active Data" Selector. Then

- Click the Edit menu and select "Interpolation Method..."
The Interpolation Method dialog box is displayed.
- Select the desired interpolation method - "Continuous" or
"Step (using closed contours only)".
- Click OK.

The **"Continuous" Interpolation Method** is suitable for initial
condition distributions that vary continuously (without breaks) in the
domain. This method performs a triangulation of the contour lines to
generate a triangular mesh (see figure).
The value at a point is computed by finding the triangle that contains
the point, and then performing a linear interpolation over the triangle.
If the point lies outside the triangular mesh, it is assigned the value of
the nearest contour. This might or might not yield the desired result. To
avoid surprises, it is recommended that either a closed contour completely
encircles the domain, or that open contour lines extend sufficiently far
outside the domain so that the triangular mesh completely covers the domain.

The **"Step" Interpolation Method** is suitable for initial condition
distributions that vary in a step like manner. *The step interpolation method
works only with closed contours. Open contour lines are ignored.* The value at
a point is assinged the value of the closest contour that encloses the point.
In the example figure all points
in the blue region is assigned a value of 0, and all points in the red region
is assigned a value of 1.

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