In Switzerland, aerial photos are indispensable tools for research into ecosystems and their management. Every six years since 1950, the whole of Switzerland has been systematically surveyed by aerial photos. In the forestry field, these documents not only provide invaluable information but also give support to field activities such as the drawing up of tree population maps, intervention planning, precise positioning of the upper forest limit, evaluation of forest damage and rates of tree growth. Up to now, the analysis of aerial photos has been carried out by specialists who painstakingly examine every photograph, which makes it a very long, exacting and expensive job.
The IMT-DMT of the EPFL and Antenne romande of FNP, aware of the special interest involved and the necessity of automated classification of aerial photos, have pooled their resources to develop a software program capable of differentiating between single trees, copses and dense forests.
The developed algorithms detect the crowns of the trees and the surface of the orthogonal projection. Form the shadow of each tree they calculate its height. They also determine the position of the tree in the Swiss national coordinate thanks to the implementation of a numeric altitude model.
For the future, we have the prospect of many new and better uses of aerial photos being available to us, particularly where isolated stands are concerned and also when evolutions based on a diachronic series of photos have to be assessed: from timberline monitoring in the research on global change to the exploitation of wooded pastures on small surface areas.