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Contour Line

The object „Contour Line“ is used - besides the object „Height Point“ - to model the topography resp. the terrain‘s profile.

By the polygon of a contour line (terrain contour) a defined height above the reference plane is defined. The height profile of the polygon is specified as with line-like objects (see Line-like Objects). Prior to the actual calculation of propagation, the final terrain profile is interpolated using the heights assigned to the terrain forming objects, applying the procedure as specified on dialog Calculation|Configuration, „DTM“ tab (see DTM Digital Terrain Model Tab) By default, the triangulation method is applied.

In the calculation of sound propagation, the terrain profile may cause screening and affect the ground attenuation. The absolute level of objects whose height has been entered as relative heights is determined from the object‘s height and the terrain model. When calculating sound propagation the contour lines are considered as being the upper edges of barriers. Terrain contours generated by interpolation (e.g. by triangulation) between the entered contour lines cause, by default, also screening (provided the option „Explicit Edges Only"“ on tab „DTM“ is deactivated, see DTM Digital Terrain Model Tab).

Note

When calculating the screening by terrain no lateral diffraction is accounted for.

On the table Contour Line (on menu Tables|Obstacles) just the first and the last point are listed (with option „Interpolate Height from First/Last Point“). The height entered is always interpreted as absolute height.

Dialog Contour Line

Dialog options

Name, ID, Memo-Window, ObjectTree

see Dialog Options Name, ID, INFO, ObjectTree, Master in the manual „Introduction to CadnaA“

Option "Use Points as Height Points"

This option offers to save a terrain model made from height points as contour lines where the vertex points of each contour receive the height of each height points (with geometry option „Height at every Point“).

In order to convert height points into a so-called height point cluster, see Height Point, Use Contour line as Cluster of Height Points.

By activating this option, the heights points making up the contour line are displayed in the graphics using the height point‘s symbol, but using the color setting for contour lines.

Button "Geometry"

see Line-like Objects of this Reference Manual

Toggling the height attribute of terrain contours

When having imported terrain contours from external file formats it may be necessary to toggle the height attribute HA_ATT (see Table Object Attributes in the manual „Attributes, Variables, and Keywords“) from „Interpolate Height from First/Last Point“ to „absolute Height at every Point“. Since the height information of terrain contours always represents absolute heights, changing the height attribute may not be possible by using the default attribute abbreviations (see chapter as mentioned above).

In this case, proceed as follows:

  • Select the command Modify Objects from the context menu of the CadnaA main window.
  • Select the action „Modify Attribute“ for the object type „Contour Line“.
  • From the subsequent dialog, select a height attribute HA_ATT.
  • Activate the option „Replace Strings“ and delete the entry under „Replace with“.
  • Click OK and confirm the action with „All“.

Afterwards, the height attribute of the contour lines is set to „absolute Height at every Point“.

Changing the height attribute HA_ATT of terrain contours