|
The paper presents a method for photogrammetric documentation of historic frescoes using workflow in photogrammetric station SocetSet designed for orthophoto production from aerial photographs. Adapted for the needs of frescoes documentation method allows variation of the internal orientation elements of images and minimizes field work by reducing the amount of test images and photogrammetric control points. Method described in the article has been tested in the documentation of Gothic frescoes behind the choir stalls in the Sandomierz cathedral. Photogrammetric registration of frescoes was made in two stages. In the first photographs were taken in the way to allow stereoscopic observations with low resolution (1 mm) and minimal amount of control points. In the second stage photographs were taken with the object resolution of approximately 0.25 mm with overlay about 10%. Stereoscopic measurement (both manual and automatic) were conducted to increase amount of control points (aerotriangulation) and to obtain digital surface model. Whereas single, high resolution photographs were taken to create resultant orthophotoplans. The adoption of a solution in which the orthophoto is generated from different pictures than those who underwent the aerotriangulation and were used to obtain digital surface model minimizes field work and reduces time-consuming computing. Collecting of stereoscopic images was conducted using quasi-aerial technique of taking series of photos with overlay around 55%. Calibrated SLR-camera Canon 5D - Mark II with 50 mm lens was used in the process. Control points were determined with an accuracy of ± 1 mm. High resolution photographs were taken with SLR-camera Canon 5D - Mark II with 150 mm lens. The pictures were taken using autofocus mode which provided highest possible sharpness. Conducted analysis of influence of variability of internal orientation elements on resultant orthophotoplans showed that in this conditions automatic focus shouldn’t reduce orthophotoplans accuracy. Digital photogrammetric station SocetSet was used to perform aerotriangulation of basic images. Then automatic measurement was performed to create digital surface model. Afterwards, using resection exterior orientation elements of high resolution images were calculated. In the end orthoimages were created and put together into one resultant orthophotoplan. The results showed that with no loss to accuracy, field and desk work can be reduced. Therefore, the described method can be successfully applied to the high resolution documentation of frescoes in other historic buildings.
|