Cut and Fill Volumes

You can obtain positive volume (cuts) and negative volume (fills) information from the CUT & FILL VOLUMES section of the VOLUME COMPUTATIONS

report. Cuts are the volume between the upper and lower surface when the upper surface is above the lower surface. Fills are the volume between the upper and lower surfaces where the upper surface is below the lower

surface. For example, you can determine the volume of a pond for which you have generated a grid file. You can define the grid file of the pond as the upper surface, and use a plane set at the level of the surface of the pond as the lower surface. The volume of the pond is the Negative Volume [Fills] volume in the CUTS & FILLS VOLUMES of the VOLUME report.

Blanked regions on either the upper or lower surface are excluded from consideration during the cuts and fills calculations.

Planar Area Calculations

Planar area is computed by projecting the cuts and fills portions of the surface onto a plane and calculating the area of the projection. Positive planar area represents the projection of the cuts (map areas where the upper surface is above the lower surface) onto a horizontal plane. Negative planar areas represents the projection of the fills (the map area where the upper surface is below the lower surface) onto a horizontal plane.

Surface Area Calculations

Volume calculations also provide you with both the positive and negative surface areas. This is the actual area of the surface. Positive surface areas correspond to the area of the surface where the upper surface is above the lower surface. Negative surface areas correspond to the area of the surface where the upper surface is below the lower surface.

As an example, consider a grid file representing the bottom of pond, with the water level at a Z value of 0. If Z = 0 is defined as the upper surface and the grid representing the pond bottom as the lower surface, you can determine the surface area of the bottom of the pond. Suppose you want to drain the pond and line it with plastic. You need to know the area of the plastic necessary to line the pond bottom. In this case, the negative surface area represents the surface of the pond bottom. This would tell us precisely the amount of plastic necessary to line the pond bottom.

Calculating Volumes and Areas

1. Choose the Volume command from the Grid menu. The Open Grid dialog box is displayed. Specify the name of the grid file or USGS DEM file to use in the volume and area calculations. This can be the grid file for either the upper or lower surface.

2. Click OK and the Grid Volume dialog box is displayed. The grid file you specified is shown for both the upper and lower surface.

3. Specify the Upper Surface and Lower Surface parameters.

* The Grid File option allows you to specify a grid file to use as the upper or lower surface. To use the grid file displayed, click the Grid File option. If you want to change the grid file for either the upper or lower surface, click the Grid File option, and then click the Browse button. After you specify the grid file, the name appears in the dialog box.

* The Constant option allows you to specify a horizontal plane to use as the upper or lower surface. You can specify the level of the planar surface by typing the value in the Z = edit box. The value you specify is in Z data units.

4. When you have completed specifying the upper and lower surface, click OK and a Status dialog box is displayed as the volumes and areas are calculated. The results are then displayed in a VOLUME COMPUTATIONS report displayed in an Editor window.

5. You can save the report in an ASCII text file using the Save As command from the Editor window File menu, or you can copy the information to the Clipboard, then paste the selected text to a Plot window or another application.