A close-range photogrammetry laboratory activity for mechanical engineering undergraduates

This paper describes a new laboratory activity used to introduce undergraduate mechanical engineering students to close-range photogrammetry mechanical engineers typically use close-range photogrammetry for the non-contact dimensioning of objects ranging in area between 10^-3 to 10² m². It is especially useful in cases where an object is visible but cannot be touched (e.g. a contaminated or fragile part), or has a complex geometry (e.g. collision damage in an automobile). While close-range photogrammetry is widely used in industrial and government laboratories and is commonly taught to civil engineering undergraduates, this technique is rarely discussed in most undergraduate mechanical engineering programs. Our photogrammetry laboratory was implemented at a very low cost, using a single consumer-grade digital camera with free photogrammetry software downloaded from the Internet (PhotoModeler Lite). Students achieved mastery of the major features of the software after about 2-3 hours of individual practice, using a series of tutorials and example images integrated into the software package. Working in 3 to 4 person groups, they then took a series of photographs of a small part using the digital camera, processed the images using the software, and compared the measurements calculated by PhotoModeler with those obtained using calipers and micrometers. Issues that affected the students ´ results included (1) quality of the lighting used, (2) camera calibration, (3) number and orientation of images chosen, and (4) ability to discern and consistently mark features of the object that appeared in more than one photograph. In post-project questionnaires completed by the students, most found the lab to be interesting and useful, and a number of them were eager to use the technique to perform measurements and construct solid models for projects they were working on in other classes.