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Scanning into the Grid

In this example each building with a building evaluation symbol assigned to has got a characteristic noise level (via dialog Modify Objects, action „Generate Building Evaluation“).

Example

Path: Examples\Extras\SmallCity03a.cna

In this example, each building has got inhabitants assigned as well...

The noise load LEG shall be evaluated for each building based on the number of residents n and the sound level L of the buildings according to:

\(LEG_{\text{Haus}}=n*2^{0.1*(L-L_0))}\) where L0 is the limiting value.

The noise load LEG shall be summed up for the entire area based on the noise grid using a scanning window with 100 m side length.

Further, a colored map shall be generated showing the noise load LEG per a reference area of 1 square kilometers (=(1000*1000) m² = 1,000,000 m²).

To achieve this, select on dialog Object-Scan via the button „Predefined >>“ the option „LEG/km²“.

Dialog Object-Scan after selection of option „LEG/km²“ from „Predefined >>“

Formula for Summation

The „Formula for Summation“ is:

prop*einw*iif(hb_gw1>0,pow(2, (hb_lp1-hb_gw1)/10), 0)

which refers to the object type „Building“ with the building elevation symbols placed inside. The formula has the following parts:

  • The condition ...iif (hb_gw1>0... is fulfilled if the limiting value for the building noise level (here: hb_gw1) is larger than zero. If this is the case the following expression is evaluated (THEN-case). Otherwise the effect is zero (ELSE-case).
  • The expression ...pow(2, (hb_lp1-hb_gw1)/10)... represents the LEG-formula as above using CadnaA specific operators. The difference hb_lp1-hb_gw1 is the difference of the characteristic building noise level and the limiting value (here, both for evaluation parameter 1).
  • The product with the number of inhabitants EINW has an effect as long as a limiting value exists. The expression PROP*EINW only considers the inhabitants proportional to the area of buildings inside the scanning window.

Formula for Total

The „Formula for Total“ (sum/area_w*1e6) is explained below:

  • The variable „sum“ itself would sum up all values LEG inside the scanning window (with area (100 x100) m² = 10000 m²) and address it to the grid point in its center. Thus, this value would not be an area related value.
  • The expression „sum/area_w“ produces, however, an area related value by division with the area of the scanning window. The result represents therefore the LEG per square meter at every grid point.
  • In order to obtain the LEG per square kilometer the expression „sum/area_w“ is multiplied by the factor (1000x1000) m² = 1,000,000 m ² = 1 km² resulting in the predefined expression „sum/area_w*1e6“.

By clicking OK the scan process starts.

Selecting a Color Palette

The resulting grid is displayed using to the presently selected color palette. Since the value range is larger, a suitable color palette has to be selected (see Color Palettes).

Open the dialog Grid Appearance on the menu Grid and select via the file selector symbol for the first evaluation parameter the global color palette „pal_0_40000_step_4000“.

Example

Path: Examples\Extras\SmallCity03b.cna

Scanning Result for parameter LEG/km² (see file SmallCity03b.cna)