Stockpile inventory of a BCG quarry

The context

BCG (Bénin Carrière Granulat) operates a granulate quarry in Benin. For the monthly material inventory close, the operator wanted a finer and faster method than the classical ground topographic survey, which took several days and had a ± 2-3 % volumetric tolerance from interpolation. The requirement: move to regular monthly tracking with ± 1 % volumetric tolerance, no operations downtime and no operator risk.

Our method

Double-grid photogrammetric flight (cross-passes, 80/70 % overlap) covering all stockpiles and working faces. Systematic layout of 6 to 8 RTK-georeferenced GCPs to guarantee centimetric absolute accuracy. Flight completed in under 4 hours, no operations downtime. Photogrammetric processing under Pix4D: dense cloud generation, triangulated 3D mesh on each stockpile, volume computed between the mesh and a reference plane agreed with the operator. Post-processing QC with GCP calibration residual check and visual artefact inspection.

What we delivered

• Centimetric orthophoto of the quarry (GeoTIFF)
• DTM and DSM of the complete operating area
• High-resolution point cloud (LAS/LAZ)
• Computed volume for each stockpile (m³, surface, heights)
• Georeferenced centroid coordinates of each stock
• Mapping of operating slope conformity
• Differential vs previous campaign (if comparison requested)
• PDF report with methodology and estimated tolerance

The outcome

BCG switched from quarterly to monthly inventory thanks to the cost and time gain. The first drone campaign surfaced a several-percent material gap vs historical estimates based on ground interpolation — a gap attributed to chronic over-estimation by manual methods. Operating slope geometric conformity is now systematically documented, easing HSE audits and authority reporting. The method has become the internal standard for monthly close.