Exercise 4: Smoothing a Surface

In this exercise, you will smooth a surface using the Natural Neighbor Interpolation (NNI) method.

This exercise continues from Exercise 3: Adding a Hide Boundary.

Smooth a surface using NNI

1. Open Surface-4D.dwg, which is located in the tutorials drawings folder.
2. In Toolspace, on the Prospector tab, expand the XGND surface Definition collection and right-click Edits.
3. Click Smooth Surface.
4. In the Smooth Surface dialog box, specify the following parameters:
   • Select Method: Natural Neighbor Interpolation
   • Output Locations: Grid Based

     The Grid Based output location interpolates surface points on a grid defined within specified polygon areas selected in the drawing. After the areas are defined, you can specify the grid X and Y spacing and orientation properties.

5. For the Select Output Region parameter, click the Value column. Click .
6. On the command line, enter Surface for the output region. This option will smooth the whole surface, rather than just the area within a specified rectangle or polygon.
7. In the Smooth Surface dialog box, specify the following parameters:
   • Grid X-Spacing: 10
   • Grid Y-Spacing: 10
8. In the drawing window, notice where some of the contour lines are especially angular. Click OK to smooth the surface.

   The display of the surface is smoothed; contours are less angular. A Smooth Surface item is added to the Edits list view on the Prospector tab.

   Note:

   The Description column in the list view displays the type of surface smoothing that was used (Natural Neighbor Smoothing). You can delete the Smooth Surface edit from the list, but this does not reverse the smoothing operation until you rebuild the surface. You can also reverse the smoothing operation by using the U (undo) command.

To continue to the next tutorial, go to Creating a Watershed and Water Drop Analysis.