Extraction of a floor plan from a points cloud: some metrological considerations

The design of evacuation plans for safety purposes is based on the graphical synthesis and visualization of data derived from high-performance measurement systems. The data post-processing requires some suitable procedures including many steps, to obtain the information needed. These are related to the global use of the measurement system, to the real measurement operating conditions, to the complexity of the building, to the simplifying hypotheses, to the data management. As a preliminary step, this work outlines a procedure for extracting a floor plan from a points cloud acquired by means of a laser scanner. The test case is a baroque cathedral, being a large structure and presenting some elements of irregular geometry. Some critical passages have been examined, presenting similar widths but different characteristics i.e., flat and regular geometries of the elements on the walls, in some cases, statues, columns and adornments, in some others. The data management plays a key-role in the correct interpretation of the outcomes, having a great impact on the results reliability. The obtained estimated variability of the passage width is in the order of few tenth centimeters. This is strictly related to the specific operating procedure. How this affects simulation software for route optimization of emergency paths will be the object of further investigations.