3D Modeling of Architectural Heritage Using UAV Photogrammetry. Case Study: Deir-e Gachin caravansary

Document Type : Research Paper


1 Master Student of Restoration and Conservation of Architectural Heritage, Department of Restoration of Historic Buildings and Textures, School of Architecture, College of Fine Arts, University of Tehran, Tehran, Iran

2 Professor, Department of Photogrammetry and Remote Sensing, Faculty of Surveying and Spatial Information Engineering, College of Engineering, University of Tehran, Tehran, Iran

3 Assistant Professor, Department of Photogrammetry and Remote Sensing, Faculty of Surveying and Spatial Information Engineering, College of Engineering, University of Tehran, Tehran, Iran.

4 Associate Professor, Department of Architecture, School of Architecture,College of Fine Arts, University of Tehran, Tehran, Iran.


Traditional survey and 3D documentation methods of Architectural Heritage are challenging, tedious, time-consuming, and error-prone due to the spatial geometry, ornament, and texture complexity in most of these structures. Recent developments in Unmanned Aerial Vehicles (UAVs) photogrammetry technology have provided a precise, rapid, and cost-effective method to generate accurate 3D models of Architectural Heritage for documentation and conservation operations, individually or in combination other methodologies. This study aims to evaluate the ability of UAV photogrammetry to produce a 3D model of a relatively complex Architectural Heritage. Deir-e Gachin Caravansary is one of the 56 Caravanserais in the Persian Caravanserais file -nominated in the UNESCO World Heritage List- which has specific architectural features chosen for this study. This caravansary is situated on the ancient route from Ray to Isfahan, located in the center of the Kavir National Park. This building bears several structural interventions during the past centuries and witnesses historical phases, from its construction in the Sasanian era to its abandonment and negligence in the late Qajar era, right up to the 21st century, when restored and adaptively reused as a tourism destination. The general workflow of this study contains three steps. The first step involves drawing data acquiring plans. Considering the features and complex characteristics of Deir-e Gachin and the possible presence of obstacles at this site to be surveyed is decided to employ aerial and terrestrial platforms to gathering photogrammetric images. In order to acquire complete documentation of the caravansary for photogrammetric purposes, two right cross flights with a ground sampling distance (GSD) of 2 cm are planned. On the other hand, four epochs are determined to acquire terrestrial photogrammetric images. At the second step, the aerial data acquisition of the rooftop and site plan is carried out by a fixed-wing UAV equipped with a non-metric camera. Afterward, two terrestrial photogrammetric processes are applied to acquiring the exterior and central courtyard facades pictures. To be able to record the exact geographic positions of the images, a post-process kinetic (PPK) GPS is attached to the camera during the terrestrial photogrammetric survey. The captured Aerial images are geotagged using the flight logs. The third step is the photogrammetric process to create an integrated and textured 3D model. In this step, aerial and terrestrial images are aligned separately by the software. The outputs of this process were two individual sparse points clouds. Then each aerial and terrestrial dense points clouds are created. Eventually, the aerial and terrestrial meshed surfaces aligned and merged to create an integrated coarse 3D model. After applying texture to the beforehand produced 3D model, the caravansary`s textured model is created. Accuracy evaluation of the result using GCPs shows an accuracy of ±2 cm in the 1:200 scaled 3D model of Deir-e Gachin caravansary. This study demonstrates the high potential of UAV photogrammetry as a fast, accurate, and reliable data acquisition method in producing a detailed exterior 3D model of Architectural Heritage structures, containing high resolution spatial, spectral, and textural information.


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