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Area-like Objects

The geometry of area-like objects (e.g. area source, parking lot, building, ground absorption) is defined by a list of polygon points with coordinates x, y and the height z. Area-like objects represent with respect to their geometry a closed polygon. In the same way, spatial objects (i.e. objects having a height, e.g. buildings) are defined by a closed polygon representing the building‘s outline in 2D projection and a height in addition.

Dialog Geometry of an area source

Dialog Options Polygon: Geometry

List of polygon points: shows the coordinates x, y, z and the ground height at the respective point. A double-click into a table row opens the dialog Polygon Point. Using the command from the context menu of the table offers - for example - to delete or insert polygon points.

List Box Height

The options are consistent with those of line-like objects (see Line-like Objects). In addition, the 2D surface is displayed:

2D-Area

area (in m²) of the polygon projected into the xy plane

Additional Information for object „Building“

Besides the geometry options for area-like objects as described above the following further points are noteworthy with buildings:

  • With reference to the underlying calculation procedures buildings are, in fact, modeled from a sequence of barriers, forming a closed polygon in the xy plane and making up an „open“ box, having no roof which is acting as a reflecting surface. Therefore, the directivity index K0 or DΩ of point, line or area sources that are located within a building‘s outline is considered based on their respective the height above the ground (and not above the roof, since there is no actual roof accounted for).
  • When a building has assigned different heights at its polygon points, the height of building will be determined based on the height of the first polygon point of the building (see Modify Order of Points in the manual „Introduction to CadnaA“).
  • When the option „Roof“ is activated, an area source that is located inside a buildings outline will receive a uniform height at all polygon points based on the height at the first building point. If necessary, select the option „absolute height at every Point“.
  • A building may also be defined with a relative height on top of a further building. To this end, activate the option „Roof“ for the inner building. In this case, the input sequence is not relevant. The underlying calculation standards just calculate the screening effect correctly with smaller buildings on top of larger buildings (like a pyramid), but not vice versa.