metria: digital photogrammetry for architecture, heritage, engineering and industry

Singular building with a great architectural and artistic interest, designed by the distinguished architect Antoni Gaudí, located on the street Nou de la Rambla, number 5, in Barcelona. It is an UNESCO World Heritage Site since 1985, and the most great and complex work of his youth, in which Gaudí undertakes a new space and formal expression way that he understands in his own personal manner and where he introduces a great number of contributions that will constitute the basis of his later repertory. The objective of our work was the photogrammetric surveying of the three facades and the building flat roof, obtaining plans at scale 1:50 with the corresponding 0.2 mm lines precision according to the ISO normative. This corresponds to a 1 cm restitution precission.

The approximate dimensions of the main facade are 24×22 meters and the street wide is just 9 meters. Therefore we have chosen a 19 mm focal lens to take the photographs. Due to the very forced angles, the lack of free clearance and the facade relief it was necessary to take the photographs from elevated positions. Covering the majority of the opposite pavement there is a hotel and residential buildings in both sides. Those buildings have terraces at 22-24 meters high, except for the hotel that is 10-12 meters higher but with a setback that hinders the use of the last floors for taking Palau photographs. The street narrowness made impossible the use of aerial photography or crane because there were angles greater than 70 degrees.

Palau Güell. Main facade. Servei de Patrimoni Arquitectònic Local (SPAL). Diputació de Barcelona.
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The back facade dimensions are 18×16 meters and the free clearance is much bigger than in the main facade. We were able to take the main photographs from some flats on the link side and from the contiguous hotel. The third series of photographs was taken from the rear Palau yard, with the limitation that there was a shade zone because of the screen. Next to the back facade we also find the 6x26 meters annexe fabric facade, which descends to the stable. For the documentation of this facade several photographs were taken from the empty space itself and from the windows. References to singular inner points were taken by means of a laser meter, to set their scale.

A redundant net with control and orientation points was established using adhesive 1cm radius circular targets and a series of visual scale and verification references using a laser distance measuring device between singular facade points and targets. The topographic targets references were taken using a total station using reflective targets. The estimated precision of this station in relative measures is 1 cm, to the order of precision necessary for establishing the levelling and control points.

Palau Güell. Rear facade. Servei de Patrimoni Arquitectònic Local (SPAL). Diputació de Barcelona.
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The remaining targets set constituted a 15 points net on the flat roof as a previous reference. The whole building roof were only visible from the hotel, that is why we decided to complete the documentation using oblique aerial photography from an helicopter using 80 and 200 mm lenses. Due to the three-dimensional nature of the roof, spire and chimneys, it was necessary to make a general three-dimensional restitution with the aim of locating each element and allowing detailed drawing of the paving. Adhesive targets were placed on points from prepared station locations that are easily differentiable, to establish the facades general orientation during the whole work.