This paper describes the projective transformations of the relief perspective of Avila Chapel in Santa Maria in Trastevere in Rome. The little Chapel was designed by Antonio Gherardi and commissioned by Pietro Paolo Avila in 1678. The research is structured according to the following steps. The Survey Model: acquisition of morphological metric data by means of 3D laser scanning and structure from motion procedures and subsequent elaboration of a Survey Model which is a mathematical representation of the current state of the architectural object. The Relief Perspective Camera and the Projective Transformations: experimentation with the ‘perspective camera’ defined by generative digital representation. The Camera is used to study the relations between the projective space and the affine space and vice-versa. Thus we can apply inverse transformations to the Survey Model in order to trace the ideal position of the projection centre. The Ideal Model: construction of the Ideal Model of the illusory architecture conceived by the author and based on the proportions and interpretation of the Survey Model transformed by the Perspective Camera. Transformation of the Ideal Model through the perspective camera and comparison with the Survey Model. History of perspective shows that there is a close connection between the theoretical evolution of relief perspective (intended as science) and its application to art, stage design and architecture. Reviewing this evolution means studying the relationship between space as it is and space as it looks