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Grid Specification

Grid Spacing and Height

On this dialog the distance between grid points in x and y direction and the receiver height in meters is specified. By default, a spacing of dx=dx=10 m and a receiver height of 4 m is used.

A smaller grid spacing results in a higher density of grid points which enhances the contours in the graphics of the lines or areas of equal sound level. On the other hand, a finer grid requires more calculation time.

absolute Grid Height

By default, the grid height is relative with respect to the ground level. In order to calculate using an absolute grid height, activate this option. In this case, the grid does not follow the terrain’s shape. This will case that grid points below terrain are ignored in the calculation.

Dialog Receiver Grid with optional features

Option „Exclude Sound Sources/Buildings“

Both options are activated by default. In this case, no grid points are placed into the horizontal projections of sound sources and buildings. Consequently, no level is calculated at those grid points.

Option „Use Height of Buildings“

By activating this option in addition to the option „Exclude Buildings“, the horizontal projection of a building is excluded from the grid if the building height exceeds the grid’s height. By default, this option is deactivated.

Make sure that the fill type of the building‘s appearance is set to „white“ when using this option (see Fill Tab). Further, you may deactivate the option „Extrapolate Grid under Buildings“ on the „General“ tab (see General Tab) in order to limit the grid to the outside of the buildings (after recalculation).

for all Variants

When more than a single variant (see Variants) is used, this option is activated by default. In this case, all active variants make use of the same grid spacing.

By deactivating this option for a variant and by entering a different grid spacing dx|dy, this option gets automatically disabled by CadnaA for all other active variants. For these variants, however, the grid spacing itself remains unchanged.

Note

In case this option is deactivated (for one or for all variants) and the grid spacing matches for all active variants, the option is activated by CadnaA for all variants automatically.

„Options“ button

Option „Define Grid over entire Limits“

With this option activated the grid covers the entire defined limits of the project file (see dialog Options|Limits), provided no calculation areas have been defined.

With this option deactivated, the calculation area can be restricted bey entering the x and y coordinates for the bottom left and the upper right corners of the grid. Alternatively, a calculation area can be used to restrict the grid’s area (see Selecting Data for the Calculation).

Example for option „Use Height of Buildings“

In this example, building 1 has a height of 10 meters and building 2, a height of 3 m. The grid’s height is at 4 m.

Example

Path: Examples\Immissions\Use Height of Buildings.cna

  • Load the addressed file.
  • Activate on dialog Receiver Grid the options „Exclude Buildings“ and „Use Height of Building“.
  • Set on the dialog Options|Appearance the fill type of the buildings to „white“.

  • Otherwise, select any type of hatching and make sure that the option „transparent“ is activated.
  • Deactivate on dialog Calculation|Configuration, „General“ tab, the option „Extrapolate Grid ’under’ Buildings“. This will prevent the lines are the areas of equal level to reach to the inside of the building’s borders.
  • Start the grid calculation (e.g. for a grid spacing of 1 by 1 m).

The following graphic results:

Grid after calculation at a height of 4 m with activated option „Use Height of Buildings“,building 2 is covered by the grid’s lines of equal sound level

Delete Grid Points

The command Delete Grid Points from the context menu of a calculation area is useful to „cut out“ calculated noise maps either to replace that portion after a new calculation or to use only a section of a big noise map. The PC-memory used for the deleted section of the grid will be released.

total grid area (white framed area: calculation area inside the present grid area By selecting the command from the context menu of the inner calculation area the grid points inside are deleted.
recalculated grid using LmE,D/N+ 3 dB in the inner calculation area total grid imported by Grid Open with option „Keep Current Grid“ activated

Insert an arbitrarily shaped calculation area over a calculated noise map, highlight the polygon and select Delete Grid Points from the context menu. Select either inside or outside the polygon. The settings of the current grid will be assigned to the imported grid.