Volume measurement - PIX4Dsurvey

How to create a new volume 

1. On the tools bar, select the Volume measurement tool by clicking or use the keyboard shortcut V.

   

2. To draw a volume, left-click on points in the 3D view. Right-click or press enter to complete the volume base polygon.
3. (Optional) To accurately mark the vertices, select the volume using the simple selection tool . The position of each vertex can be corrected in the 3D view, on the images, or using the vertex editor.
4. (Optional) To assign a common elevation to the vertices of the volume base surface, first select the volume using the simple selection tool . Then, in the Properties panel , click align vertices to choose how to align the vertices.
   

After drawing the volume, details about the volume measurement are displayed in the Properties panel . More specifically:

Note: A new volume layer can be added by selecting the icon of the volume layers on the left sidebar. The volume can be moved to another volume or vector layer by right-clicking on it.

How to compute the volume

Once the volume is drawn, in the Measurements section of the Properties panel, click Compute to trigger the volume computation.

After completing the volume measurements, the cut/fill volumes and errors are displayed.

More specifically:

• Cut volume [units³]: Volume above the volume base. The volume is measured between the volume base and the surface.
• Fill volume [units³]: Volume below the volume base. The volume is measured between the volume base and the surface.
• Net volume [units³]: The absolute difference between Cut and Fill volume (Cut - Fill volume)
• Total volume [units³]: The total volume (Cut + Fill volume).

Important: If the polygon defining a volume is modified (adding/removing/moving vertices), a warning appears in the Volume layers list and the Export tab, indicating that the volume measurement is now outdated.

It is needed to compute the volume again to take the modifications of the volume polygon into account in the volume measurement.

How to export a volume or volume report

After computing the (cut/fill) volume measurements, the Volume report, the volume polygon and the 3D volume are available to be exported.

To export the Volume report:

1. On the Menu bar, click File, then Export. Alternatively, on the top right, click Export. The Export panel opens on the left.
2. (Optional) Unselect the output Volume layers that do not need export.
3. In the Export panel, select the output format (PDF, HTML, or CSV for volume reports. LandXML for the 3D volumes. DXF, ZIP SHP, SHP, or GeoJSON for the volume polygon).
4. In the Destination section, navigate to the path where the files should be saved.
5. Click Export.

How PIX4Dsurvey calculates the Volume measurement

PIX4Dsurvey calculates the volume as follows:

1. A new volume is drawn. For more information on how to draw a volume: How to create a new volume.

2. PIX4Dsurvey projects a grid with GSD spacing on the base.

3. For each cell i of the grid, its volume (V_i) is given by:

V_i = L_i * W_i * H_i

Where:

L_i = the length of the cell.
W_i = the width of the cell.
H_i = the height of the cell.

The Length (Li) and Width (Wi) are equal to the project's GSD.

L_i =W_i = GSD

The Height (H_i) is given by:

H_i = Z_Ti - Z_Bi

Where:

Z_Ti = the terrain altitude of each cell at the center of the cell.
Z_Bi = the base altitude of each cell at the center of the cell.

Therefore, the volume V_i of cell i is given by:

V_i = GSD*GSD* (Z_Ti - Z_Bi)

4. PIX4Dsurvey calculates 2 volumes:

• The Cut volume V_c is the volume between the base and the 3D terrain when the terrain is higher than the base.

Cut volume = V_C = V_C1 + V_C2 +...V_CN

Where:

V_C1...N = Cut volume for cell i..N

• The Fill volume V_F is the volume between the base and the terrain when the terrain is lower than the base.

Fill volume = V_F = V_F1 + V_F2 +...V_FN

Where:

V_F1...N = Fill volume for cell i...N.

5. The Total volume is given by:

Total Volume = V_T =V_C+ V_F