We have to assure that all buildings which may shield any of the calculation points, and thus affect the noise levels at one or more calculation points, are included in the terrain profiles to be used in Novapoint Noise.

The data about buildings in the terrain model may vary a lot. In most cases, the data included will not give a correct representation of the buildings in a terrain profile. Examples A and B in the figure below show what a terrain profile with a building may look like when the building is defined by an outline with a specified ground level and roof edge.

To get a correct representation of the buildings in a terrain profile, the buildings have to be recorded as Novapoint Noise buildings.

A Novapoint Noise building consists of an outline at the roof edge level and a ridge with indicated height. In addition, connecting lines are drawn between the corners of the outline and the ends of the ridge (the gables).

Outline and ridge with heights may be collected from the terrain model to Novapoint Noise (see New og Fetch). The data is collected from the map in AutoCAD, and not directly from the terrain model.

a)The terrain profile is generated directly from the terrain model, outline height is given for the ground level, the building is not included in the terrain profile.

b)The terrain profile is generated directly from the terrain model, outline height is given for the roof edge level, the profile of the building is completely wrong.

c)The building is registered in the Noise program, the profile is correct.

A terrain profile intersecting a Novapoint Noise building example c) in the figure, is supplemented with extra points where the terrain profile crosses either the outline, the ridge or the gable of the building. The heights of these points are read from Novapoint Noise (the height of the points where the profile meets the gable is interpolated from the height of the outline and the ridge). To get a correct terrain profile, one point is added one mm in front of where the terrain profile first intersects the building (point d1 in the figure), and one point one mm behind the last building intersection (point d2 in the figure). The height of these two points is interpolated from the terrain profile as it was before the building was added. Points from the original profile located between the points d1 and d2, are removed, thus leaving a profile where the building is represented correctly.

By having the buildings registered in Novapoint Noise, we have a better control of the heights of roof edges and ridges. Furthermore, buildings which lack a complete description may be changed or supplemented. The user is also allowed to move buildings or define new buildings.

To avoid having to add a ridge to all buildings, the buildings may be described as a block without ridge and with a roof edge height equal to the height of the ridge. This simplification will normally affect the noise levels insignificantly, but one still has to consider this in advance.

All buildings that may shield any calculation points have to be registered in Novapoint Noise so that we get them into the terrain profiles which are used in the calculations, in a correct manner. Novapoint Noise reads height data on the buildings directly from the read-in map in AutoCAD. This means that the feature codes holding building data must be read in 3D from the terrain model to AutoCAD. Novapoint Noise uses the layer name in AutoCAD as an indication on what is buildings and which height is given to the building. The table below shows these relations.

???????? Suggests that there are 8 characters that might vary first in the layer name
* Suggests that there might be more characters in the layer name

Buildings that might lay in other layer names than stated in the table above will not be fetched in to Novapoint Noise, unless you change the standard settings in the dialog box Layer name for fetching buildings.

To get the overview of how buildings are defined in the terrain model, we have to have a look at each and every building and check that feature codes and heights are according to what is comprehended by Novapoint Noise. Click a point on a building line, height and feature code for the point will be shown. By clicking a contour line at the building, the terrain level may be compared with the level of the building line.

If the buildings have the same feature code, but someone has given height to the ground level, someone has given height to the roof edge, the user will have to change the feature codes for the buildings, one at a time. This is done by making drawings of all buildings (feature codes other than 5000 series should be set to passive) in the terrain model.

If a feature code is consistently used wrong (e.g. if feature code 5001 is used where 5002 should be used), we either have to change them in the terrain model (recommended) or change the standard settings in the dialog box Layer name for fetching buildings in Novapoint Noise.

It is important that the buildings are orderly defined. There should be an outline and possibly a ridge for each building. Other lines in connection with building normally have to be set passive or to be deleted.