1. A method of determining a triplet of parameters defining a ground plane in a three-dimensional reference frame on the basis of a depth image obtained from a sequence of images, comprising: selecting valid points from the current depth image, the valid points being the points of the image whose distance from a point of origin of the three-dimensional frame of reference is in the range between a predetermined minimum distance and a predetermined maximum distance, determining an indicator R 3d for the current depth image, said indicator being dependent on the number of valid points in the current depth image, and on the total number of points in this image, selecting a set of points of interest in the current depth image, each point of interest being selected if a distance between said point of interest and the ground plane determined for a previous image in the sequence is below a threshold d sel , determining a triplet of spatially filtered parameters on the basis of points of interest, and determining a triplet of temporally filtered parameters as a function of the indicator R 3d determined for the current depth image or for a previous image in the sequence.