Working with Reality Model Classifiers
A Classifier is a set of one or more elements that are linked to the reality mesh to provide a method for identifying portions of the mesh that represent physical entities. Two dimensional shapes from GIS (Geographic Information Systems) applications are particularly convenient and valuable as they typically are geographically located and contain valuable property data. By using design data to classify the reality model, you are able to access the reality model as a set of intelligent components rather than a single, isolated entity. The link between the reality model and the underlying design data is bidirectional so you can either query the GIS model to locate the associated reality mesh or select locations on the reality model to access the underlying design data.
Example: Classifiers of the Philadelphia Reality Model
In 2015, a reality model of Philadelphia was created to support the Pope’s visit to Philadelphia. In order to demonstrate Reality Model Classification, we will link this model with GIS data and explore the value of this combination. Like most municipalities, the GIS data for Philadelphia is readily available. The website www.opendataphilly.org provides over 300 different datasets. Let's start by downloading the building footprint data in SHP format.
The SHP data can be opened directly in MicroStation and saved to DGN format for convenience. We also directly open the reality model in the .3mx format created by the ContextCapture software and save that to DGN.
Once you attach the classification, it will appear in the lower list box of the Reality Mesh Attachment dialog and is set to be the Active Classifier for the reality model attachment.
In most cases, it is preferable to use Classifiers to control how the reality model is viewed without changing the reality model attachment. It is, however, possible to use the reality mesh clipping tools to permanently clip the model at classification boundaries. For example, in the zoning example above, it is possible to create separate attachments for the commercial zones by selecting the zones (<Ctrl+Click> will allow selection of more than one classification boundary) and using the Split Reality Mesh tool to create separate attachments for each zone and a single attachment for areas outside the selected boundaries.
Point and Linear classifiers
2D Linear geometry is important in GIS, Civil and other disciplines as it is often used for roads, railroad tracks, waterways or boundaries. Point data is frequently used to represent locations of interest or vertical assets such as street signs or telephone poles. Although this geometry alone does not enclose an area that can be projected to produce a classification volume, it may be combined with the Margin setting to produce classification volumes that enclose and surround the geometry.
Example: Philadelphia with Arterial Streets Classifier
In the previous examples, 2D GIS data has been used to classify the reality meshes. In this case, the 3D geometry is projected to classify all reality model geometry above (or below). It is also possible to use 3D geometry to more precisely enclose reality mesh volumes. Currently, volumes can be specified by slabs, cylinders and non-parametric extrusions. If other 3D geometry is used, then the classified volume is determined by the range of the element.