Design of an automatic scaling approach for photogrammetric point clouds of micro features

A novel application of photogrammetry is consisting in measurement of microfeatures. 3D model reconstruction, high resolution measurement and good accuracy can be obtain with a low cost equipment. However, in order to obtain high performance in measurement, 3D geometry obtained by photogrammetry needs to be calibrated for setting the scaling factor. Using commercial software, the scale is commonly retrieved through two different procedures: the first one consists in using a known distance between two markers within the images, the second procedure consists in placing the camera/s in known positions. Both procedures need accurate and expensive facilities when the photogrammetry is applied on microfeatures measurement. In the present work an automatic and low cost method to find the correct scale factor for a photogrammetric 3D model applied at micro-scale is presented. The method is based on automatically retrieving blurring area combined with Depth from Focus method.