Calcul des surfaces. Atouts et limites des récepteurs GPS "grand public"

Abstract

General-purpose GPS receivers are becoming increasingly popular as a result of their low cost and ease of use. Some offer a function for computing surface areas directly in the field, a major benefit for many foresters. Experiments have been conducted to assess the limitations of these devices for the purpose of direct surface area calculations. In open landscapes, the mean over-estimation of one hectare is 1.6 % with an error margin of ±1.6 %. The actual surface area therefore lies (for a probability threshold of 5 %) within an interval [- 3.2 %, 0 %] from the measured value. Accuracy improves and bias decreases the larger the surface area measured. On the other hand, a forest canopy increases the bias and adversely affects accuracy: on a surface area of one hectare, the over-estimation is 4.1% on average with an error margin of ±12 %. The actual surface area therefore lies within (for a probability threshold of 5 %) an interval [- 7.9 %, + 16.10 %] from the measured value. The acceptability of this error margin is discussed.