## Intro to Reverse-Engineering

Q. What is reverse-engineering?

A. Stepping backwards from a finished design, analyzing how it can be re-created, usually for the purpose of modification, enhancement, or re-production.

Q. Why would we want to reverse-engineer?

Reverse-engineering is used for far more than simply re-creating commercial products (making a "knock off"). Throughout history, many of mankind's best scientific advances have been the result of reverse-engineering designs from nature.

In modern times, reverse-engineering has become ever more important. Today many products are intentionally made to break or to become obsolete. For such objects to continue to be useful instead of heading for a land-fill, reverse-engineering plays a vital role, allowing makers to extend the life of their tools and every-day items.

Reverse-engineering is also an outstanding outlet for creativity and personal expression, allowing creative people to customize and personalize the items we carry with us every day.

In this third lesson of Practical Printing we will walk through a reverse-engineering exercise based on a common device - a tablet.

### Reference Images

Reference images are vital for reverse engineering and can be obtained any number of ways. We will focus on two methods - a 2D scanner, and a camera.

#### 2D Scanner

The big advantage of using a scanner is that items scanned will be preserved at accurate scale when we attempt to use them in a CAD software.

Of course the down-side of a 2D scanner is that many objects will not fit properly in the scanner so it's use may be limited.

#### Camera

Using a camera allows us to take a wide variety of reference images. But there are a significant number of disadvantages as well:

* Lens distortion - ALL photographic images suffer from lens distortion, and the smaller the lens the more they tend to distort. This can play havoc with the accuracy of reverse-engineering.
* Orientation - it is difficult to orient objects relative to a camera in a way that provides good reference surfaces.
* Shadows, tricks of light, etc. - These can all make it difficult to cleanly re-create designs.

### Exercise 1: Reference Images

We will use a combination of techniques involving both the scanner and a camera.

* Scan the two faces of the ipad
* Using a level, set up a shoot for the other surfaces of the ipad including the bottom, top, and sides

### Exercise 2: Photographic Editing

We will prep our images before bringing them into modelling software. This is important, as it is virtually certain that the images will have a certain amount of rotation in them, along with the lens distortion. Use Inkscape to remove rotation in the scanned images, and clip them.

The images taken by camera will not know their scale, and so they will need to be fixed in scale along with rotation. (They should not have a perspective problem, provided the images were taken at perfect level)

### Exercise 3: Reference Images in CAD

Learn to bring images into FreeCAD and orient them on their correct planes. In Inkscape, a common graphic/vector editing software we will learn to:

* Rotate Images
* Create a clipping mask
* Scale a clipped image
* Export a corrected image

### Exercise 4: Modelling

Learn to model using the photographic reference material. Topics covered include:

* Multi-body modelling
* Use of the "additive pipe" (also known as a sweep)
* Using boolean operations (for cutting out ports)
* Cloning bodies
* Slicing bodies as prep for printing