1. A method for correcting a volume imaging equation for more accurate determination of a velocity field of particles in a volume, said volume being captured from different directions by at least two cameras, a coarse calibration of the position of the cameras relative to each other and relative to the volume of concern being carried out first by determining an imaging equation that associates with the coordinates (X, Y, Z) of a point in the volume the corresponding camera picture coordinates x i , y i , of each camera i, all the cameras then capturing simultaneously in the same unchanged position particles in a volume, the position (X, Y, Z) of a particle in the volume being approximated by means of a known triangulation method using the calculated position x i , y i , of a particle in the camera pictures, this position (X, Y, Z) being imaged through the original imaging equation onto a position in the camera images of the at least two cameras, a correction factor for the imaging equation being calculated from the difference (dx i ′,dy i ′) between the coordinates (x i , y i ) and (x i ′, y i ′) so that, thanks to an amended imaging equation, the point (x i , y i ) becomes identical with the point (x i ′, y i ′) M for all the cameras i, this correction occurring for many particles in the volume.