Harvesting inventories which involve the counting of all exploitable species are labour intensive operations often neglected by the forestry companies. A full inventory is nevertheless the foundation of a traceability system, which is now required of all companies seeking forest certification as a way of assuring the legal origin of harvested wood. We propose an inventory method that is improved by the use of GPS receptors. The method has the advantage of more precise positioning of each tree, and allows, thanks to the information captured automatically by the GPS, a more effective monitoring of the work of the inventory team. For example, the GPS allows a supervisor to track the exact route walked by each team member and the number of hours worked. Above all, the GPS allows the generation of a digital terrain model based on point measurements of altitude, which resolves the problem, frequently encountered by foresters in the tropics, of inaccurate or inexistent maps.