Reverse Engineering (RE) is a multidisciplinary scientific method that can be applied to several different fields. Although in broad sense the term Reverse Engineering is used in many different areas (e.g., from software code development for decode the mechanism of a function, to Internet network security), the version of the concept considered in this course is the digital reconstruction of a physical object or environment, starting from a set of 3D data captured in the real world.

The course aims at illustrating the operating principle of the various 3D sensors currently available on the market, framing them in a general context, specifying their functions and motivating their performance. A substantial practical laboratory activity is planned, during which the students, through two group exercises, develop digital 3D models of real objects both with active and passive techniques.

After passing the exam, the student:

1. knows the theoretical principles of 3D measurement;
2. knows the basic terms and principles of active and passive sensor measurement technologies;
3. knows the characteristics of the principal instruments usable for a 3D survey;
4. Knows the process workflow to go from a real object to a digital 3D model;
5. Is able to analyse an object or scene to survey and identify the most appropriate measurement system;
6. Is able to determine in advance the problems of a survey and adopt the appropriate solutions;
7. Is able to characterize or calibrate an instrument;
8. Is able to select and execute the working pipeline to obtain a result appropriate to the requirements of the specific work (for example accuracy, resolution, number of model polygons);
9. Is able to motivate its design choices and communicate the results of its activities in a clear and convincing way.

Theoretical introduction

General information on 3D measurement methods, with and without contact.

Nature of light.

Light-matter interaction.

Taxonomy of non-contact systems based on different forms of radiant energy.

Passive and active 3D sensing techniques.

Active 3D sensors

3D measurement for triangulation:

Laser scanner with single spot, single light plane, multiple light plane.

Full-field measurement based on fringe projection.

Active systems based on measurement of distances:

3D flight time measurement (TOF); direct estimation of flight time (PW); indirect estimation of flight time (CW); indirect estimate of flight time (FM-CW).

Principles of 3D metrology

Characterization of the errors of a range device.

Study of the possible artefacts generated by an active sensor.

Construction of polygonal models from acquired data

Topological concepts.

Working pipeline: draft project; acquisition, meshing; alignment; (Iterative Closest Point algorithm); merge; optimization; editing.

Passive 3D sensors.

Principles of photogrammetry.

Chamber calibration.

Structure from motion, image matching, generation of dense 3D clouds.

Creating models from images.

Standard software packages for the realization of the entire Reverse Modeling process with active and passive techniques.

Previous knowledge of photography and CAD modeling are welcome.

The overall evaluation will be based on:

• 1 multiple choice theoretical test, based on the contents illustrated in class and the bibliography texts (personal evaluation).

The test is structured in order to verify the expected learning outcomes from 1 to 4.

• 1 exercise with active acquisition techniques (group assessment).

The exercise aims at verifying the learning related to the expected outcomes from 5 to 8.

• 1 exercise with passive acquisition techniques (group assessment).

The exercise aims at verifying the learning related to the expected outcomes from 5 to 8.

• A critical presentation of the work carried out at the end of the course (group assessment).

The presentation aims to verify mainly the learning outcome expected in point 9.

In Modeling and Simulation in Engineering, Catalin Alexandru (Ed.)