Ana Elena Seguí

Integration of Laser Scanning and Imagery for Photorealistic 3D Architectural Documentation

Documentation of architectural and archaeological sites and monuments is an activity that requires the capture of information from different sources. Metric information is mandatory as the basis for documentation, information management, archiving, analysis, monitoring and dissemination activities, among others. In highly weathered environments, accurate 3D models are required for multi-temporal analysis over time in 4D, altogether with imagery. Experience has shown that it is possible to provide the necessary information with the required accuracy and completeness only by integration of multisource data (Georgopoulos & Ioannidis, 2006). Especially in large and complex monuments parallel use of geodetic and surveying measurements, photogrammetric data acquisition with imagery and terrestrial laser scans has proven to be the ideal combination (Haddad, 2007; Haddad & Ishakat, 2007). Furthermore, the multi-sensor integration of surveying data (not only terrestrial but also aerial) and architectural needs should be combined with a multi-resolution approach, spanning from few centimetres down to millimetres, if necessary, both in geometry and in texture (Guidi et al., 2008; Remondino et al., 2009). A general overview of the typical requirements and solutions for cultural heritage documentation based on purpose, product, methodology or eventual emphasis is presented in Patias (2006). Modern technology has changed matters in documentation radically and promises to keep bringing rapid changes. Photographic and non-photographic (graphic) documentation tools are merging in one process, in which the digital photographic technology is the main base (Haddad, 2010; Haddad & Akasheh, 2005). Until the wide spread used of terrestrial laser scanning (TLS) for cultural heritage documentation, most of the multi-temporal information for documentation and conservation activities was based mainly on graphic documentation: 2D drawings of elevation plans, cross-section and last but not least, images (analogue or digital). However, photographs are easier to interpret and recognize than drawings; they contain information about surface detail and can provide information on the condition of a monument, before, during, and after restoration. Nowadays, the afore-mentioned documents are still requested by architects or building personnel but the analysis is starting

Integration of TLS Data and Non-metric Imagery to Improve Photo Models and Recording - A Case Study on Djin Block No. 9, Petra (Jordan)

In this paper we present a methodology to accurately derive 3D photo models of a World Heritage monument by means of terrestrial laser scanning (TLS) and close range photogrammetry. TLS will provide 3D point clouds as well as rough photo models that can substantially be improved draping texture with external imagery. The tomb Djin Block No. 9 in Petra is used to compare texture results delivered by the camera of the terrestrial laser scanner versus an external off-the-shelf digital camera. The issue of image resection and calibration of non-metric single imagery is tackled making use of a digital surface model. The presented approach is suitable for off-the-self digital cameras and can cope with single images without overlap. Results show that it is possible, on the one hand, to enhance photo models draping external imagery onto the 3D model, and on the other, to take advantage of single non-metric images to record cultural heritage.

Grey Level and Noise Evaluation of a Foveon X3 Image Sensor: A Statistical and Experimental Approach

Radiometric values on digital imagery are affected by several sources of uncertainty. A practical, comprehensive and flexible procedure to analyze the radiometric values and the uncertainty effects due to the camera sensor system is described in this paper. The procedure is performed on the grey level output signal using image raw units with digital numbers ranging from 0 to 212-1. The procedure is entirely based on statistical and experimental techniques. Design of Experiments (DoE) for Linear Models (LM) are derived to analyze the radiometric values and estimate the uncertainty. The presented linear model integrates all the individual sensor noise sources in one global component and characterizes the radiometric values and the uncertainty effects according to the influential factors such as the scene reflectance, wavelength range and time. The experiments are carried out under laboratory conditions to minimize the rest of uncertainty sources that might affect the radiometric values. It is confirmed the flexibility of the procedure to model and characterize the radiometric values, as well as to determine the behaviour of two phenomena when dealing with image sensors: the noise of a single image and the stability (trend and noise) of a sequence of images.