Terminology can be confusing in this area of work. Sometimes words and phrases are completely logical when referring to a particular method or technique such as “front projection.” A phrase can be unfamiliar, but the process it describes is actually quite intelligible as may be the case for "screen resolution." Other times, not only is the term utterly unfamiliar to the average person, but the process it describes seems exotic and highly specialized.
"Mapping" is an example of the exotic. It succeeds in shrouding the process of aligning imagery with architectural features and proportions of two dimensional planes or three dimensional objects completely. It can be daunting to understand mapping even to the point where projection designers simply use the word to describe what they want and then hand the task over to specialists. The first time I modified imagery to fit the proportions of a screen surface, I was completely unaware I was "mapping" anything. I opened my software and adjusted the parameters until the imagery looked right. If this approach works for you then you probably never really have to concern yourself with what "mapping" really means.
Many projects these days require a more sophisticated approach because mapping has been employed successfully on many well publicized projects. It has been used for product launches or opening ceremonies - recordings of which find vast audiences via the internet. This has led to many more directors, designers, creative agencies and promotors to ask for "mapping." Of course, many of these projects had a small army of specialists employed to produce the desired result. The theatre in comparison is a modest environment compared to a product launch for a large, multinational corporation. The technical concept behind the implementation of mapped imagery is the same, but the solutions vary widely depending on what kind of mapping you endeavor to employ. I wrote more about the principle of mapping here, but below is little recap...
The concept of mapping was first employed in large scale theatre projections back in the 1960's. Back then, technicians and designers referred to it as "pre -distortion." Richard Pilbrow describes the process in vivid detail in his recent book A Life In Theater. Together with his colleagues from Theatre Projects, he developed a method that could be employed on any project. He understood the limitations of projectors, optics and what it means to use these within the architectural constraints of the theatre. He put a camera into the scale model of the set design and took a picture of the projection surface. The position of the camera is crucial. It must be in the same position as the projector to be rigged. The lens of the camera also must be equivalent or close to that of the projector. Thus, the camera looks at the projection surface in the model exactly the way the real projector will "look" at the real set. The crucial idea here is the following: when you make the virtual reality match the physical reality, the imagery matches. Virtual reality can also be less virtual as in the the case of Richards’ approach - a scale model instead of a computer model. The important criteria is that the proportions, distances and and positions of all elements, notably projectors, optics and screens are the same as they will be in reality, such as in the theatre venue. There is much more to this in practice depending on the particular application or project. I would like to clarify the different approaches in the hope to demystify some of the phrases commonly used:
2D mapping: mapping to one or more two dimensional objects or planes that are always at the same distance and angle to the projector(s).
2.5D mapping: mapping to one or more two dimensional objects or planes that are at varying distances in 3d space. This can also be decribed as a simulation of 3D mapping, but all objects are two dimensional. These objects can be curved, but they have no depth.
3D mapping: mapping to two or three dimensional objects that are at varying distances and varying angles to the projector(s) in 3d space.
What type of mapping is the most adequate for a given project depends largely on the level of integration the imagery is supposed to have with the physical set and lighting design. A significant factor is whether the projected imagery is supposed to move with a piece of scenery as that piece moves. This is commonly referred to as automation tracking, scenic tracking or simply tracking. In this context, one thing is alreday clear; if a piece of scenery moves and the imagery is supposed to stay aligned with that piece of scenery, it happens in a three dimensional space. Why this matters become clearer as I talk about the types of mapping in more detail in the next couple of parts to this series.