Al Nasri House
Building Conservation
The Al Nasri House is an historic earthen structure located in Al Ain Oasis, within the UNESCO World Heritage serial property ‘The Cultural Sites of Al Ain’ (Hafit, Hili, Bidaa Bint Saud and Oases Areas). Although it has deteriorated substantially over time, the structure that remains alludes to an example of vernacular architecture in the oasis.
Photo of the northern wall, with scaffolding.
Terrestrial photogrammetry.
Photogrammetric model of the northern wall with the scaffolding masked.
Damage mapping of the north façade. Mapping on orthophoto (left).
Drawing of damage mapping (right).
Materials mapping. Mapping on orthophoto (left). Drawing (right).
The team members discussed the methodology for documentation which included determining the desired outcomes for the case study and the survey techniques to be used. As the earthen building had deteriorated substantially and was at high risk of further decay.
The survey comprises
spatial level 2 and 3.
The goal of the case study was to develop a metrically accurate model of the surviving elements of Al Nasri House at a high level of detail 3 with high quality imagery to identify the current condition.
Photographs were taken with a
high-quality digital camera to produce a photographic portfolio for the site, and for use in the photogrammetric applications. Careful consideration was given to the lighting and quality of the captured photos, and a colour correction palette was used for photo enhancement prior to the development of the
photogrammetric models.
Colour correction was performed on the photographs taken for the photogrammetric model. This was necessary to produce an accurate, quality graphic image of the model.
Following colour correction, metrically accurate photogrammetric models were created using Agisoft Metashape photogrammetric software. This included masking the scaffolding to produce an unobstructed model for easier pathological analysis.
Damage mapping was conducted for the north wall of the house which displayed significant damage due to water infiltration, fallen palm trees and inappropriate interventions. Intervention mapping was conducted for the west façade which had undergone several alterations over time, many of which were inappropriate from a conservation standpoint.
The photogrammetric model was used to create orthophotos for the desired façades. Orthophotos allowed for an accurate and highly detailed representation of an element projected onto a given plane — and therefore provided a useful tool for the documentation of the historic environment.
The orthophotos were exported as .TIF files and were imported into AutoCAD to create the damage/intervention map drawings. The drawings were created following the standardised AutoCAD template, including use of the appropriate layering system and legend of decay, as discussed in the HED Standards. Drawings: Intervention map of the west façade, identifying the various alterations that have been implemented over time. Damage map of the north façade, identifying the various conditions and damages that had developed over time.