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Structuring Data by Defining Groups

A group is a selection of objects which is based on a predefined expression based on the ID. For these groups of objects different actions can be carried out, for example:

  • deletion,
  • conversion into a different object (e.g. converting a line source into a road or a railway),
  • transformation of object coordinates,
  • activating or deactivating objects for calculation,
  • representation of results etc.

The groups are defined via menu Tables|Group.

Table Groups with two groups (Tables menu)

Objects are associated with a group by specifying a character string („Expression“) being part of the object’s ID. In the above example all objects whose ID starts with the letter A are belong to the group „actual“ (i.e. actual situation). All objects, however, whose ID starts with the letter P are belong to the group „planning“ (i.e. planning case). The asterisk (*) is a wild card substituting all further characters of a string.

Group dependent Actions

When groups are defined, actions can be restricted to all objects of an existing group. On the dialog Modify Objects, a list box is available listing all groups in the present project.

By the action in the following figure all roads of the group „present“ would be deleted.

Deleting all roads of group „present“

In principle, actions available on the dialog Modify Objects can either be applied to all objects or be restricted to the objects within an existing group.

Example

With sources organized in groups, their respective partial levels are displayed on the group table. For example:

  • Enter two groups of 10 point sources each.
  • Draw a section around the left group of point sources.

A section delimiting the 10 point sources on the left

  • Click with the right mouse button on the section’s border and select the command Modify Objects from the context menu.
  • Select the action „Modify Attribute“, as range“ „Inside Polygon“, and as object type the point source. Now, click OK.

Modifying an attribute of the point sources inside the section

  • On dialog Modify Attribute, select from the list box „Attribute“ the item „ID“ and enter for „Replace Strings, Replace with“ the following string: compressor_##.

Replace Strings: Modifying attribute ID

  • Click OK and confirm the action with „All“.

In the next step, a different ID will be assigned to the sources outside the section.

  • Again, click on the section’s border with the right mouse button and select the command Modify Objects from the context menu.
  • The action and the object type selected are retained. Deactivate the range „Inside Polygon“ and activate the range „Outside Polygon“.
  • Click the OK-button.

Modifying an attribute of the point sources outside the section

  • On list box „Attribute“ the „ID“ is still selected.
  • Change the input for „Replace with“ to: ventilator_##.
  • Click OK and confirm by „All“.

The sources inside the section have an ID starting with „compressor...“ while the sources’ ID outside starts with „ventilator...“. In either case the ID is followed by an underscore and a counting number.

Now, an emission level is assigned to all sources. To simplify, all sources receive an A-weighted sound power level of 100 dB(A).

  • Click into the white area of the CadnaA main window and select the command Modify Objects.
  • The selected action („Modify Attribute“) and object type („point source“) can be kept.
  • Click OK and select from the list box the attribute "Lw_Li" which represents the numerical emission value PWL.
  • Enter on „Replace Strings, Replace with“ the value: 100.

Emission: sound power level of 100 dB(A)

  • Click OK and confirm by „All“.

As can be seen from the table for point sources (menu Tables| Sources|Point Source) all point sources have received an emission level PWL of 100 dB(A). In the next step, three receiver points are entered and two groups are defined.

  • Select the receiver point from the toolbox and enter three receiver points.
  • Address a name to the receiver via the respective table (menu Tables|Receiver). Click into each table cell in column „Name“ and type RCVR1 to RCVR 3. You can immediately write to the table cell. Click the „Close“ button.
  • Click into the white area on the screen and select the action „Generate Label“ for the receivers and click OK.
  • Select the attribute „Name“ and click OK.
  • Confirm the action with „All“.

Now, all receiver points are labeled by their name.

  • Open the Group table on the menu Tables.
  • Click with the right mouse into the group table and select command „Insert after“ from the context menu.
  • Repeat the procedure to attach a second row.
  • Type into the first line as a name „compressors“ and as expression „c*“. Thus, all objects starting by the letter C will belong to the first group.
  • Type into the first line as a name „ventilator“ and as expression „v*“. Thus, all objects starting by the letter v will belong to the second group.

  • Close the table Groups and start the calculation by clicking the pocket calculator-symbol on the symbol bar.

  • Now, reopen the group table.

Partial Level day per group for three receivers

On the table Groups the partial levels of each group for the selected performance parameter (Day) at all three receiver points are displayed.

  • Double-click into the first line of „compressors“.
  • On the dialog Group click the button „Partial Level“.

The subsequent dialog lists the A-weighted partial levels at all receiver points by all sources within this group and for all performance parameters (on this example: for Day and Night).

Partial Level list for group „compressors“

Via the context menu command Sort (right mouse button) those values can be sorted for the column selected, e.g in a descending order.