The basic requirement for automatic conversion of DXF files is that (a) they should be in DXF version 12 format (not 2012!); (b) Drawing units in Metres; (c) at real-world rectangular co-ordinates; and (d) each layer should contain only one type of object.
Unfortunately, architectural drawings often do not comply with these requirements because the originators are more interested in visual appearance than in geometric consistency. Modern drawing packages allow different elements to be drawn at different scales and then superimposed. The eye can integrate the various elements to make to comprehensible picture, but NoiseMap cannot do this.
To ensure easy conversion, you need to stick to the conventions of Ordnance Survey MasterMap or Landline datasets. A particular problem is that often the OS Mastermap is regarded as a 'pictorial' background to the scheme drawings, so its layers are often flattened into a single layer. This means that although the eye can distinguish roads, buildings, and other features, they are not longer identified by digital properties so fully automatic conversion is no longer possible.
Architects often set the drawing units to millimetres which gives greater precision for fine details, but NoiseMap will see an object with a dimension of 1000 as being a kilometre long, whereas it was intended to be a metre long. So models can end up being thousands of kilometres in size.
This problem can now be handled by NoiseMap. If you know that a model has units of one millimetre, you enter the following in the command pane at the bottom of the log/results window:
set dxfrealscale 0.001
All the DXF co-ordinates (including height) will now be scaled by this factor.
You can set any scale you like: for example, if a drawing is scaled in feet, you can convert it to metres as follows:
set dxfrealscale 0.3048
All objects must be completely within the positive quadrant (ie to the east and to the north of the origin). Be aware that because the origin of an architectural drawing is probably not at real-world co-ordinates, some objects could be in the negative area (shaded pink in NoiseMap). In this case, you will get an invalid tile error when saving. You will have to shift the objects (using edit>modify object coordinates) so that they are in the positive quadrant before saving.
As a final caution, CAD software can now produce 'solid' 3-D models, where objects are stored as 3D surfaces rather than 3D lines. NoiseMap cannot interpret 3D surfaces, but 3-D lines are ideal.
