### 30.1.2. Three Dimensional Interpolation

3D interpolation functions can be used to specify any quantity in CFX-Pre for which a standard CEL function (for example, `sin`, `cos`, `step`, and so on) can be used. The function is created by interpolating values between a “cloud of points” using a distance weighted average based on the closest three points. Common applications include setting an initial guess or a profile boundary condition from experimental data values.

For a 3D interpolation using the `Interpolation (Data Input)` option, you should set X, Y, and Z coordinate values and a single value associated with the coordinate. The coordinates and the value are interpreted in the local coordinate frame, which will depend on where the function is used. For example, if the function is used to set a boundary condition value, the coordinate frame selected for that boundary condition will apply. For details, see Coordinate Frames and Coordinate Frames in the CFX-Solver Modeling Guide. If the local coordinate frame is cylindrical, the units for the Argument List should still be those of a Cartesian frame.

Data for 3D interpolation can be entered manually or read from a file. If the file contains data in the profile data format, then it can be imported as described in Profile Boundary Conditions in the CFX-Solver Modeling Guide. Otherwise, numerical values for the 3D interpolation can be imported directly into CFX-Pre using the instructions below. Also see Importing Data from a File for more information on how to import the numerical values from a file.

1. Enter a unique function name that you will use when setting the value of a quantity using an expression.

2. Argument Units: Enter a comma separated list of the units used for the coordinates.

   These will usually be coordinate axis dimensions (for example, `[m]`, `[cm]`, and so on).

3. Under Result Units, enter a single unit.

   This unit should be a valid unit for the quantity you will be specifying (for example, [`m s^-1]` for a velocity).

4. Right-click in the window to import data from a file or delete an entry.

5. Enter a comma, separating X, Y, Z coordinate values.

   The coordinates are interpreted in the local coordinate frame, which will depend on where the function is used.

6. Enter a Value associated with the Coordinate.

7. Click Add to add the point to the list (or Remove to remove a highlighted value from the list).

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