Principle of Pre-Processing


WallMan can pre-process urban and indoor databases. This is required to enable intelligent ray-tracing in ProMan (faster than standard ray-tracing), and is optional for several other simulation methods. In the pre-processing, the building data are prepared for the prediction. Also, errors in the database are corrected.

The main advantage of pre-processing for ray-tracing is that the simulations will be faster. On the other hand, depending on the settings, prediction height and discretization are specified before pre-processing and cannot be changed later in ProMan.

Empirical Models

The pre-processing for the empirical prediction models consists of a check of the different objects within the building database. Both the definition of every single object itself and the interaction between different objects are verified. In the urban mode, the pre-processing for the vertical plane models (COST 231 Walfisch-Ikegami, knife edge diffraction model) determines also the pixels which are located inside the buildings. This means that the prediction grid is fixed (concerning lower-left corner and resolution) after the pre-processing.

Standard Ray Tracing

The pre-processing for the standard ray-tracing performs the same building check as for the empirical models. Additionally, for the urban mode, the visibility relations between walls can be computed and stored, which increases the computation time of the pre-processing slightly but reduces the time at the prediction.

Intelligent Ray Tracing

The pre-processing for the intelligent ray-tracing requires a longer computation time because detailed visibility relations are computed and stored in a file. This procedure reduces the computation time of the prediction significantly.

Parameter Files

Multiple parameter files for one input database (IDB file for indoor and ODB file for urban) are possible. This allows the user to compute different types of pre-processing (different parameters, different areas) for the same database.

These parameter files (suffix PIN for indoor and suffix PRE for urban) can easily be generated with WallMan using clear dialogs. The pre-processing itself is also performed in WallMan.

Coordinate System

In principle, WallMan can work with all Cartesian coordinate systems (for example, UTM or Gauss-Krueger) for both urban and indoor applications. Although the coordinates are referred to as metric unit, other units can be used.

When computing a pre-processing to do a prediction, the database must be converted to the metric unit at first. This can be done with the function Scale all objects from the Objects menu.

This is important because the calculations of free space losses are calibrated to the metric unit.