Applicable plans
Lake
Valley
Ridge
Mountain
Peak
You have collected survey data at two different time steps and you want to calculate the volume difference between both surveys.
Principle
To calculate a volume difference you need to perform 2 steps:

It is important to select an arbitrary reference plane that does not intersect with the stockpiles at any of the time steps.
That's why we recommend using sea level (0,00 m) as the Reference Elevation value.
Step 2: Calculate the difference between the obtained values.
Note: This technique provides you with a total cut or fill value for the specified area. The spatial distribution of the materials within the polygons is not taken into account.
Quick guide

Open the terrain created using the data from the 1st survey.

Then add the 2nd survey to this project. Go to the Insert tab > Terrain and click the Elevation button.

Select the elevation terrain created using the data from the 2nd survey.
 Click Open and the elevation terrain will be added to your project. Hence, you will have the elevation data from both time steps loaded in one project.

Draw the polygons around the stockpiles you want to use in the volume calculations (Home > Drawing > Polygon).

Go to the Home tab > Volume Operations and set the Reference to Flat.
 Set the Elevation value in a way that assures that your Reference plane does not intersect any of the stockpiles, e.g., 0,00 m.

Calculate the volumes of the stockpiles (Home > Volume Operations > Calculate Volume). Since the elevation layer from the 2nd survey is enabled, these are the volumes from the 2nd survey.

Uncheck the elevation terrain in the ProjectTree. The elevation of the first survey will become active.

Calculate the volumes again using the same arbitrary Reference level. These are the volumes from the 1st survey.

Export your volume information. Both volume calculations will be exported.
 Calculate the volume difference using the data you exported. This can be done, for example, in Excel.