Two apparatuses developed in our laboratory and based on the same principle are described and tested. They semi-automatically acquire the 3D location of dots making up a network at the surface of wood-products in order to measure the resulting displacement field. The location of each dot is achieved by means of an image analyser coupled with a 2-axis robot to determine the location of the barycentre in the corresponding plan. The third co-ordinate is obtained through a displacement sensor. The accuracy of each device is studied and discussed through the analysis of repeated measurements performed on three products such as: small oak plank (150x120x27 mm), commercial size oak plank (1930x150x30 mm), 3ply cross-laminated douglas fir panel (390x390x6 mm). Two kinds of testing are performed: A-Test without motion of the sample to assess the accuracy in dot detection, and B-Test corresponding to a real measurement where no variation of moisture content has occurred and which theoretically leads to displacements equal to zero.