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UAV-DAP (unmanned aerial vehicle-digital aerial photogrammetry) has become one of the most widely used geomatics techniques in the last decade due to its low cost and capacity to generate high-density point clouds, thus demonstrating its great potential for delivering highprecision products with a spatial resolution of centimetres. The questions is, how should it be applied to obtain the best results? This research explores different flat scenarios to analyse the accuracy of this type of survey based on photogrammetric SfM (structure from motion) technology, flight planning with ground control points (GCPs), and the combination of forward and cross strips, up to the point of processing. The RMSE (root mean square error) is analysed for each scenario to verify the quality of the results. An equation is adjusted to estimate the a priori accuracy of the photogrammetric survey with digital sensors, identifying the best option for µ (weight coefficients depending on the layout of both the GCP and the image network) for the four scenarios studied. The UAV flights were made in Lorca (Murcia, Spain). The study area has an extension of 80 ha, which was divided into four blocks. The GCPs and checkpoints (ChPs) were measured using dual-frequency GNSS (global navigation satellite system), with a tripod and centring system on the mark at the indicated point. The photographs were post-processed using the Agisoft Metashape Professional software (64 bits). The flights were made with two multirotor UAVs, a Phantom 3 Professional and an Inspire 2, with a Zenmuse X5S camera. We verify the influence by including additional forward and/or cross strips combined with four GCPs in the corners, plus one additional GCP in the centre, in order to obtain better photogrammetric adjustments based on the preliminary flight planning.

[EN] Special Section Preface, [ES] Prefacio de la Sección Especial

Augmented Reality (AR) applications have experienced extraordinary growth recently, evolving into a well-established method for the dissemination and communication of content related to cultural heritage-including education. AR applications have been used in museums and gallery exhibitions and virtual reconstructions of historic interiors. However, the circumstances of an outdoor environment can be problematic. This paper presents a methodology to develop immersive AR applications based on the recognition of outdoor buildings. To demonstrate this methodology, a case study focused on the Parliament Buildings National Historic Site in Ottawa, Canada has been conducted. The site is currently undergoing a multiyear rehabilitation program that will make access to parts of this national monument inaccessible to the public. AR experiences, including simulated photo merging of historic and present content, are proposed as one tool that can enrich the Parliament Hill visit during the rehabilitation. Outdoor AR experiences are limited by factors, such as variable lighting (and shadows) conditions, caused by changes in the environment (objects height and orientation, obstructions, occlusions), the weather, and the time of day. This paper proposes a workflow to solve some of these issues from a multi-image tracking approach.

The use of photogrammetry and terrestrial laser scanning for building information modelling (BIM) in the documentation and conservation of Cultural Heritage (CH) is now well established. By combining BIM with the latest visualization technologies, powerful, semi-immersive experiences can be developed to enhance the dissemination of CH. In semi-immersive experiences such as Augmented Reality (AR), digital content can be overlapped on to physical spaces, providing a new way to interact with both the physical space and the digital content. This paper discusses the translation of a digital object created using BIM, into a physical object and the utilisation of this physical object as a trigger for an AR experience. The case study looks at one of the neo- Gothic window frames from the House of Commons in the Centre Block of the Parliament Hill National Historic Site, in Ottawa, Canada. The window frame is one in a series that represents a Canadian province or territory with a stained glass feature that includes floral emblems and heraldic symbols from the respective provincial or territorial shield. The frame in this case study corresponds to the stained glass window of five provinces. Using the replica frame as a target, the user can select which stained glass windows they would like to view in the AR application. Through these combined technologies, we argue that CH can be revealed in a more interactive way and therefore more engaging manner - making even inaccessible architectural details readily available to the public.

In recent years, Augmented Reality (AR) technology has experienced considerable progress and the combination of AR and 3D modeling opens up new opportunities regarding 3D data visualization and interaction. Consequently, the dissemination of cultural heritage can benefit from these technologies in order to display the cultural assets as realistically and interactively as possible. In this way, high-Accuracy 3D models are integrated in the real world.