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Grid Arithmetics

By the grid arithmetics different grids can be combined with each other. For example, effects resulting from reflection, screening or triangulation can be rendered visible in a easy and informative way. The dialog Grid Arithmetics (on the Grid menu) enables to load up to six grid files and to perform calculations thereof.

Example

Let us see how a barrier changes the sound contours. Proceed for this as follows:

  • Enter a point source at (x,y,z)=(100,100,0.5), and a receiver at (x,y,z)=(200,100,1.5).
  • Enter a calculation area using the mouse or the keyboard (e.g. with the corner coordinates ((x1,y1)=(50,150), (x2,y2)=(250,150), (x3,y3)= (250,50) and (x4,y4)=(50,50)).
  • Start the grid calculation with a receiver spacing of 1x1 m and with appearance setting „Raster, Oversampling=1".
  • Save the grid (menu Grid|Save as) with the file name "without barrier“.
  • Enter a barrier via the keyboard reaching from (x1,y1)=(150,75) to (x2,y2)=(150,125) having a height of 6 meters (dialog Geometry).

Editing a barrier height of 6 m

  • Recalculate the grid and save the resulting grid again via menu Grid|Save as using the file name „with barrier“.

grid (with progressive colors) showing the barrier effect, using the gobal color palette pal_35_85_step_5

Calculating the Level Difference on the Grid

  • Open the dialog Grid Arithmetics and select using the respective file selector symbols the grid file named "without barrier" for grid R1 and the file "with barrier“ for grid R2.
  • Enter for the first evaluation parameter (here: Lde) the expression r2. Thus, the resulting grid for the first evaluation parameter is the level distribution with barrier.
  • Enter in the line for the second evaluation parameter (here: Ln) the expression r1-r2. Since the screening effect is added in the calculation of the receiver level, this expression will return the barrier attenuation Abar in dB on the grid (Abar = Lw/o barrier - Lwith barrier).
  • Click the button OK to apply those expressions.

Dialog Grid Arithmetics: Calculating the grid of level differences

Selecting a Color Palette for Evaluation Parameter 2

The color palette "pal_35_85_step_5" selected in the grid appearance for the evaluation parameter 1 is, by default, also applied to all further evaluation parameters 2..4 and the ground grid. Consequently, this color palette is not suitable for the second evaluation parameter Ln as this grid is showing a difference level: The entire grid is displayed in green colors. To improve the representation for evaluation parameter 2 proceed as follows:

  • Open the dialog Grid Appearance and activate the tick mark in front of evaluation parameter 2.
  • Select via the file selector symbol in line „Eval. Parameter 2“ the color palette „pal_0_20_step_2“ from the global library of color palettes by a mouse click and then click the button OK.

Color palette „pal_35_85_step_5“ for evaluation parameter 1 andcolor palette „pal_0_20_step_2“ for evaluation parameter 2 selected

  • Close the dialog Grid Appearance by OK.

With those settings for each of the evaluation parameters a different color palette is used.

Difference grid (with progressive colors) showing the screening effect (barrier attenuation Abar)

Modifying the Evaluation Parameters Name

Now, the name of evaluation parameter 2 shall be corrected for as it is a level difference.

  • Open the dialog Configuration in the Calculation menu and select the „Evaluation Parameters“ tab.
  • Activate the tick mark in column „Name“ of evaluation parameter 2 and enter the text „DeltaL“.

  • Close the dialog with OK

Now, on the list box for the evaluation parameter on the CadnaA main „DeltaL“ instead of „Ln“ is displayed.

Displaying a Grid Legend

The object „Symbol“ () from the toolbox enables to display a grid legend with respect to the evaluation parameter selected.

  • Select the symbol and draw a rectangle to the left of the calculation area.
  • Click with the right mouse button on the symbol’s border.
  • On the dialog, select from the list box „Symbol“ the option „Legend: Grid“.
  • Close the dialog with OK.

Now, when toggling the evaluation parameter the respective grid legend is displayed.

Applying the Object „Level Box“

In addition, the object „Level Box“ () from the toolbox can be used to display the level at distinct locations on the grid.

  • Select this object from the toolbox and click at any location inside the grid.

Difference grid with grid legend and level boxes