Surface comparison - PIX4Dmatic 

Surface comparison

The surface comparison tools allow you to compute volumes by comparing two different surfaces, such as point clouds or TINs, instead of relying on a single base surface.

This approach is particularly useful when you need to quantify changes over time or between design and as-built conditions, for example, measuring earthwork progress, stockpile depletion, or fill and cut between successive surveys. 

From surface

Using this combo box allows to select the reference sufaces for volume computation. It is possible to select one or multiples point clouds or a single TIN.

PIX4Dmatic will prevent mixing these data types. Once a Point Cloud is selected, all TIN options in the list will be disabled (and vice versa).

To Surface

Using this combo box allows for selecting the surfaces to compute the volume against the surfaces selected in the previous section. The surface selected in the "From surface" section will be disabled in this combo box.

Apply boundaries

In this section, you can select the layers that contain geometries to be used as boundaries. Supported geometry types include volumes, polygons, circles, and polylines with more than two vertices.

If a layer contains multiple geometries, PIX4Dmatic will compute one volume for each individual geometry using the inputs selected in To surface and From Surface.

Filter by

If the point cloud used in the computation is classified—either with terrain and non‑terrain classes or following the standard ASPRS scheme— it is possible to select the specific class that contains the relevant data and use only that class for the calculation.

Only the classes that contain points will be displayed in the list of classes.

Resolution

• Default. Average GSD 
• Custom. Since imported point clouds do not have original camera metadata, a 'Synthetic GSD' is calculated. This is based on the Point Cloud Scale, which is the average distance between neighboring points. To ensure the highest level of detail is preserved without creating artificial gaps, the system uses the average point spacing from the most dense point cloud as the project's base resolution.

Layer

The result is stored in a layer. This can either be a new layer created after the computation or an existing layer selected from the project.

Properties panel

For volumes generated with the Surface comparison tool, the Properties panel displays a “From surface” combo box in the Recompute section. If the volume was computed using the Volume tool, this combo box is not available.

Before recomputing a volume, verify that all input parameters are correctly set, including the selected point clouds or TINs and any applied class filters.