Calculating the Z Value of the Surface at a Point
The Grids  Calculate  Point Sample command samples Z values from a grid at any point. To perform the operation, create a data file with X and Y coordinates for the points you'd like to sample and click the Grids  Calculate  Point Sample command.
Example
Consider a grid file that ranges from zero to 10 in the X and Y dimensions, and you want to determine the value of the surface at the points (1,3) and (4,2) on the surface.

Open a new worksheet window with File  New  Worksheet.

In column A, type the X coordinates for the points you wish to find the Z value, e.g. type 1 in Row 1 and 4 in Row 2. In column B, type in the Y coordinate, e.g. type 3 in Row 1 and 2 in Row 2. Add as many points as you want into the data file by entering the coordinates for each point into a different row in the data file.

Use the File  Save As command and enter a name for the data file, for example PointSample.dat. Click Save and the XYZ data file is created.

Click the Point Sample command.

Specify the Input Grid, XY Data, and Data Columns in the Point Sample dialog.

Click OK and a worksheet is opened with the Z values from the points you entered.
See Also
Calculating the Agreement between a Grid and the Original Data File