MACRO PHOTOGRAMMETRY IN INVENTORY OF HISTORICAL ENGRAVINGS AT THE ROYAL CASTLE IN WARSAW
Keywords: macro photography, SfM/MVS, engravings, the Royal Castle in Warsaw (Poland)
Abstract. In the community historical objects play the role of witnesses of the past history. This creates an obligation to preserve and reconstruct them for future generations. Photogrammetric methods have been applied for those purposes for many years. In the process of development of inventory documentation, the key aspects related to the selection of appropriate measuring methods for particular objects and the creation of appropriate working conditions. At present, digital measuring techniques allow developing 3D photogrammetric documentation which is particularly valuable both, for conservators of historical objects, as well as for creating virtual museums. Particular attention should be paid to the utilisation of macro photography for that purpose which allows for recreating small fragments of historical details. The objective of this paper is to present possible use of macro photography for inventory of historical patterns engraved in brick walls of one of the cellars of the Royal Castle in Warsaw (Poland); they are called engravings or house marks. The cellar walls were made of bricks (20 × 10 cm) on the stone foundations, where a prison was located in the 17th century. Prisoners left their drawings of signs and crests. Bricks are destroyed, some of them are moss-grown, so many engravings are hardly visible and their depths vary between 3 and 5 mm. The Canon 5D Mark II camera with the 50 mm macro lens was used to inventory engravings together with the shadow-free flash, mounted on the lens and a special frame with bolts, being the photogrammetric control network. To ensure the high quality of the 3D model, a network of photographs were acquired from two different distances; they were processed with the use of SfM/MVS algorithms implemented in Agisoft PhotoScan software. The aim of this paper is to discusses the impact of selection of control points on the accuracy of the orientation process, the impact of the point cloud density on correct projection of the digital surface, the influence of the DSM resolution on details of projection of shapes and selection of orthorectification and mosaicking parameters on the accuracy of orthoimage generation.