Il quartiere storico di Raksila a Oulu, Finlandia. Rilievo laser scanner e analisi per la tutela e gestione del patrimonio archtiettonico ligneo nel paesaggio urbano scandinavo

The survey has been performed at the urban scale, considering the relationship between historic architecture and new buildings. The strong characterization of the houses has been fully documented by using the laser scanner technology, allowing the creation of a detailed metrical archive that has produced inventories and typological analysis on the elements constituting this architecture.

Two main objectives settled in this research for defining the structure of the documentation:

• The need to improve and develop updated digital survey techniques applied specifically on Nordic Heritage;
• The need to produce detailed inventory analysis with the main scope to increase the state of the art on the cases analysed.

The study started with a careful planning of the practical phases involved. Different scales of investigation, which from the general aspects include progressively the details, produce different levels of analysis and consequently different levels of values. This system of investigation contributes the elaboration of a multidisciplinary research that considers the object in its whole material and immaterial configuration. Three main criterions guided the actions:

• Preliminary recognition of the area, with archival investigations;
• Definition of the objectives, expected results and limits;
• Organization of the practical survey activities.

During the preliminary recognition, it is important to define the activities involved in the process, elaborate operational schemes in order to identify all the different typologies of the data obtained and to understand the achievable results. “Input-Output” schemes, tables and lists can help the researcher in the organization of the work and give important insight in the elaboration of cross checks and transversal implementations.

During the second and third steps, the identification of the different objectives and expected results helped the recognition of the scale of investigation and the organization of the practical activities that, in general, go from the general aspects includeing progressively the details.

The analysis of the case study of Raksila has been conducted through three main steps:

• Realization of an updated digital documentation of the site;
• Evaluation of the tangible and intangible values by making cross checks of the data (archival materials and information obtained on field);
• Definition of the actions and strategies of interventions for the preservation of the authenticity of the place.

In addition to the survey and to the technical activities, the case study of Raksila has represented the testing ground for the application of the main articles of the Venice Charter and demonstrating one of the main point fixed in the Declaration of Amsterdam: “The architectural heritage includes not only individual buildings of exceptional quality and their surroundings, but also all areas of towns or villages of historic or cultural interest”[1].

According with the objectives defined, the second part of the work concerns the practical activities concentrated in collecting updated information and metrical data on site:

• Laser scanner survey, from which obtain a complete point cloud both of the architecture and its environment;
• GPS survey, in order to georeferenced the point cloud and be able to allocate different parts of point cloud in a mutual geometrically and georeferenced correct position. The GPS survey helped also the reduction of the error during the registration phase of wide areas;
• Direct survey by using simple tools for measuring details and parts which cannot be surveyed by the laser scanner;
• Photo Documentation not only for general observations, but mainly for the elaboration of the photo-maps of the facades, and for the construction of a digital Photographic Archive;
• Photo modelling reconstructions, by using the possibility to reproduce from 2D photos 3D mesh models with the structure-from-motion SFM process;
• Census activities, for the creation of descriptive inventories and technical atlases of the buildings investigated;
• Additional activities: landscape analysis, studies related to environmental and cultural aspects by using interviews and external supports from other specialized technicians.

Objectives, criterions, practical survey steps have defined an interdisciplinary and wide method essential for the analysis at the urban scale and understanding of this context.

Survey activities produced a big amount of data and updated documentation, characterized by different typologies of information: metric databases of the point clouds, vector 2D drawings, 3D models and thematic maps produced by the combination of the different levels of information.