The Riddle of the Crosses: The Crusaders in the Holy Sepulchre

Abstract

This paper describes the rationale, the challenges and the imaging solutions employed in an attempt to uncover a centuries-old riddle. We suggest an answer to the meaning of the hundreds of crosses, inscribed on the walls and behind the altar of the Chapel of Saint Helena, within the Church of The Holy Sepulchre in Jerusalem. Traditionally, these crosses have been ascribed to the Crusaders of the 12th and 13th centuries, but our research suggests a different chronology. A variety of photographic and photogrammetric imaging technologies have been utilised, along with traditional archaeological research, in an intensive attempt to document as much empirical data as possible during a short period when renovations to the chapel created a small window of opportunity for access. Despite considerable difficulties relating to time and location, three primary goals were set: (1) to capture a 3D representation of the curvature and depth information of the walls covering an overall high-resolution grid of all the stones behind the two central apses; (2) to make a detailed RTI representation of selected stones; and (3) to analyse the chiselling technique of the crosses and decipher the inscriptions and heraldic symbols found near the inscriptions. Three main imaging techniques were employed: 2D panoramic high-resolution Gigapan photography, 3D photogrammetry, and Reflectance Transformation Imaging. The results of the data collected are currently undergoing analysis in an attempt to establish the chronology, typology, and stratigraphy of the incisions. We hope that this will assist in confirming, correcting or rejecting the traditional explanations ascribing the graffiti crosses to the Crusader period. Analysis of the chiselled incisions on the stone reveals regular V-profile grooves. The angles are determined by using a photometric stereo ('shape from shading') image processing technique to determine the surface normal-vectors at each pixel position. Issues relating to the non-ideal 'real-world' conditions of capturing the images will be discussed, including camera movement, ambient light, and accuracy of light position coordinates from the highlights on the billiard ball.