Designing with images
– Augmented reality supported on-site Trompe-l'œil 

1. Overview 
The use of computers in architectural practice is widespread and complements traditional tools such as drawings and physical models. Computers can support the entire design process in three dimensions; however, output devices are still generally ‘traditional’ 2D devices, such as screens.
Rapid technological advances are enhancing the possibilities of architectural design, for instance 3D VR and AR environments. Immersive and semi-immersive projection displays, such as CAVEs are already used to support VR applications in many professional domains, including the field of architecture. However, the visualisation of data using these displays requires dedicated rooms for setting up non-mobile screens, and allows one to interact with purely virtual information only.
Our research project aims to liberate the architect from these artificial environments by enabling the ad-hoc visualisation of interactive 3D (stereoscopic) and 2D (monoscopic) data on arbitrary surfaces in real-world indoor environments. This is a prerequisite for developing systems that can support the design process in real-world environments.
The project is an interdisciplinary research project with two core areas:
1) Technological basis – core technology
2) Computer-supported architectural design

2. Supporting on-site design in existing buildings
The main aim of the project is to develop solutions that support the architectural design process in existing buildings, based upon the new mobile projection technology. The projection technology enables one to project data in real-time onto almost any surface of an existing building, colour-calibrated and geometrically rectified to fit the real context. The setup can be positioned freely, much like pointing a torch. The technology makes it possible to provide both purely immersive virtual environments as well as to augment real situations with additional virtual data to show changes in surfaces of objects. 

The paper describes and discusses the concept behind new novel approaches for the immersive formulation of design intentions such as an ar-based form of (interactive) on-site Trompe-l’œil. Trompe-l'œil is an art technique that employs realistic imagery to create the optical illusion that the objects depicted really exist, although they are actually 2D paintings. 
In the paper we will describe the concept und the core functions of the application in more detail:
1) The use of “predefined” (2D) building element images together with ad-hoc interactive (monoscopic) projection within real environments.

2) The capture and cropping of “real” building elements (e.g. doors) or sections of surfaces (e.g. mural) in real-world indoor environments and the use of these images for formulating design intentions.  

3.) The ‘fading-out’ of “actual” building elements or sections of room-surfaces based on an optical overlay of textures or surface structure from neighbouring regions (using different methods, e.g. tiling textures, texture synthesis).

4) Ad-hoc interactive optical illusion projection (based on an innovative tracking method and a perspective-rectified monoscopic projection with depth effect).

5) Laser-pointer interaction in real environments – a new kind of input device employing a normal commercially available laser pointer. 

Certain aspects of the concept have been implemented and tested as prototypes. These will be presented and discussed at the end of the paper.