Traditionally for a custom made orthotic to be made, a negative cast needed to be taken of the foot. Now with all the lines being blurred between the different types of foot orthotics and the newer technologies being developed and the older methods being more widely used, I prefer to use the term: Negative Model Production to encompass all the different methods.
These methods include things like:
1) The traditional slipper plaster cast
2) The STS sock
3) Optical scanner
4) Digital photography
5) Foam box methods
6) Pins (eg Amfit)
7) Wax sheets
8) Silicon beads
10) Mental imagery
Obviously, we have to stop using the term 'casting' to cover the wider concept of negative model production.
To expand on the last two methods. Extrapolation refers to those methods that use 2D plantar pressures to determine the 3D shape of a foot (even thought I think that this is a scam, its still out there in the marketplace and needs to be added to the classification).
I included 'mental imagery' as a negative model production method as this is the process we go through in visualising the foot before deciding on which prefabricated foot orthotic to use.
All the methods have there pros and cons (and have you noticed that the proponents or marketers of each method all claim theirs is the best?). Whichever method is used depends if it can achieve the orthotic design parameters for the prescription variables needed.