Receiver Grid

On the menu Grid the following features are available:

• specifying the spacing and the height of grid points (see Grid Specification),
• launching grid calculations (see Grid Calculation) for up to 16 variants (see Variants) and for up to four evaluation parameters (plus the ground grid, see Evaluation Parameters Tab),
• selecting the type of appearance of the grid/noise map (e.g. as lines or areas of equal sound levels, see Grid Appearance),
• commands to open, save, delete, compress/decompress and to resample grids.

Calc Grid

The grid calculation for the specified evaluation parameters and the defined grid spacing is launched by the command Calc Grid (see Grid Calculation).

Select Evaluation Parameter

Selects the grid for the corresponding evaluation parameter from the list box on the toolbar on the CadnaA main dialog.

Grid|Open

With the command Grid|Open a saved grid can be loaded into the present file. Select the corresponding file via the dialog. Using multiple selections several grid files can be loaded at once. A grid cannot be loaded via the command File|Import.

different Evaluation Parameters

In case a grid file contains several grids with different evaluation parameters they will only be displayed if the same evaluation parameters also exist in the current file.

Grid Formats

Following grid formats can be opened:

• CadnaA-grid (*.cnr) and CadnaA-files (*.cna)
• ESRI ASCII-grid (*.asc, *.hdr): Both, non-proprietary ASCII raster files (*. asc) as well as proprietary binary raster files (*.hdr) are imported.
• ASCII-grid (*.rst)
• LimA grid (*.ert)
• SoundPLAN grid (rlk_.*;*.gm)
• Immi grid (*.ird)
• AUSTAL grid (*.dmna)
• NMGF grid (*.grd, from NMPlot, TNM, INM)

option „Keep Current Grid“

When the option „Keep Current Grid“ is activated you can load grids in the current file without deleting the existing ones. The first existing calculated grid in the current file sets the mash of the grid. With different grid spacings of the present and the loaded grids, the resulting grid will be adjusted to the original by interpolation.

This function enables the calculation of a large file using several calculation areas on different computers sharing the file by calculating only one of the calculation areas one after the other. Afterwards all the grids will be merged into the original file via command Grid|Load with the option „Keep Current Grid“ activated (see PCSP - Program Controlled Segmented Processing).

Save Grid as

With the command Grid|Save as only the calculated grids will be saved, so not the object data. The following file formats are available:

• CadnaA-Grids (*.cnr)
• ASCII-Grids (*.rst)
• LimA Grids (*.ert)
• NMGF Grids (*.grd)
• GeoTiff (*.geotiff), 1 Band, 32Bit FLoating Point-Werte

When saving to an ASCII grid the evaluation parameters as entered or edited will be used as a designation (see dialog Configuration, Evaluation Parameters Tab).

Furthermore, grid data can be exported as lines or areas or as an ASCII file for ArcView (see ESRI Shape (*.shp)).

Text file with ASCII-grid data for 4 evaluation parameters (format *.rst)

Grid|Delete

By the command Grid|Delete the existing grid (for up to four evaluation parameters, plus the ground grid) is deleted and from the file (upon Save). This command cannot be undone.

When deleting a grid, the settings for the grid spacing and for the grid appearance are kept. However, when selecting the command Grid|Delete while keeping the SHIFT key pressed restores the default settings for grid spacing and grid appearance.

Delete Grids in Variants

Selecting the command Grid|Delete while keeping the CTRL key pressed will delete - after having confirmed a prompt - all grids in all variants.

Grid|Compress, Decompress

By the command Compress on the Grid menu grids resulting from former CadnaA releases can be compressed in order to reduce their volume. By contrast, the raster data from files created with CadnaA release 4.3 or later will be compressed automatically upon calculation.

The command Decompress enables to decompress the raster data resulting from releases starting from 4.3. Decompressing grids is required when grids having different calculation areas shall be combined (see Grid Arithmetic).

Additional Information

The background of these two commands is the requirement to further reduce the disk space required for large-scale grids, in particular. This is advantageous when loading, storing and calculating grids.

In CadnaA, prior to release 4.3, the grid area saved at tilted calculation areas was given by the smallest enveloping rectangle. In fact, the grid area always represented a rectangular section within the limits whose edges were parallel to the coordinate axes xy.

Starting from CadnaA release 4.3 just those grid points are saved which are distinctively located inside the calculation area(s), thus causing a compression of the grid when being saved.

Example

The example below shows a tilted calculation area. When saving the grid with a release version prior to 4.3 all the points within the left red rectangle have been saved. This also comprises the grid points which are located outside the calculation area.

In contrary, the right red rectangle delimits the grid area, which is stored starting from release 4.3. This area corresponds to the calculation area.

Saving of Grid Data prior to release 4.3	Saving of Grid Data from release 4.3 on

Grid|Resample

The command Resample offers to interpolate a grid with a given receiver spacing into a new grid with a different receiver spacing.

Dialog Resample Grid

On the dialog Resample Grid enter the new receiver spacings dx and dy. After clicking OK, the resampling is processed.

Resampling is possible starting from a coarser grid (larger receiver spacing) to a finer grid, but also starting from a finer grid (smaller receiver spacing) to a coarser one.

Note that in particular when resampling a coarser to a finer grid the intermediate grid points are generated using linear interpolation. Moreover, by „up-sampling“ and then “down-sampling“ - obviously - the initial grid cannot not be regained.

Application

Resampling may be used in conjunction with grid arithmetics (see Grid Arithmetic) when rearranging several input grids with different receiver spacings to a common resulting grid.

Example

(displaying the grid points as dots)

	initial grid (10 x 10) m
	initial grid resampled to (2.5 x 2.5) m receiver spacing
	initial grid resampled to (50 x 50) m receiver spacing
	resampled grid (50 x 50) m again resampled to (2.5 x 2.5) m receiver spacing The valid grid size has reduced because - due to the resampling to (50 x 50) m spacing - a part of the grid no longer exists (i.e. lying outside the calculation area).