Hello @mathias.h​ ,

Am I correct to assume this is a terrestrial 3D point cloud? Yes, creating a solid by surfacing the points is perhaps the most accurate approach. However, a good approximation could be made by dividing the tunnels into sections, using the min/max per section (retrieved from the PointCloudStatsCalculator) to calculate volume (the smaller the tunnel sections, the more accurate the results). Just depends what method you'd like to explore.

Here to help,

Kailin