Linear referencing > Displaying and querying route events
Dynamic segmentation |
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Release 9.3
Last modified February 24, 2009 |
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Geographic data is represented on a map as a layer. Route events are no different. To display route events on a map, however, you must first define the parameters of the relationship between the table storing the events and the routes that the events reference.
The dynamic segmentation process
Dynamic segmentation (DynSeg) is the process of computing the map location (shape) of events stored in an event table. Dynamic segmentation is what allows multiple sets of attributes to be associated with any portion of a linear feature.
The result of the dynamic segmentation process is a dynamic feature class known as a route event source. A route event source can serve as the data source of a feature layer in ArcMap.
For the most part, a dynamic feature layer behaves like any other feature layer. It is possible to decide whether to display it, the scale at which it should be visible, what features or subset of features to display, how to draw the features, whether to store it as a layer file (.lyr), whether to export it, and so on.
A route event source can be edited in ArcMap. It is important to note that it is only possible to edit the attributes. The shapes of a route event source, however, cannot be edited, because they are generated by the dynamic segmentation process. When you edit a route event, you are actually editing the underlying event table. As such, there may be some editing limitations imposed by the event table. For example, it is not possible to directly edit the attributes of a route event source created from a delimited text file table, since ArcMap does not allow text files to be edited directly.
Advanced dynamic segmentation options
Point events as multipoint features
When a point event is located along a route, a point feature is created. In some applications, however, route measures are not unique. For these applications, it might be desirable to have point events treated as multipoint features.
Event locating angles
When a point event is located along a route, it is often desirable to know the angle of the route where the event is placed. For example, you might need to rotate the marker symbol that is used to display the event so it is oriented to the route and not the map. Further, you might need to rotate a point event's label.
The dynamic segmentation process can calculate either the normal (perpendicular) or tangent angle. Further, it is possible to calculate the complement of these angles so that you can, for example, control the side of the route on which a rotated label appears.
Event locating errors
The dynamic segmentation process creates a shape for each row in the input route event table. In some cases, however, the shape of the event feature might be empty. This happens when there is a reason that the event can't be properly located. In other cases, an event can only be partially located; this happens for line events only.
The dynamic segmentation process can expose locating errors—if any exist—for each event in an event table as a field. This field is very useful when performing quality assurance tests on your event tables.
Event offsets
In some applications, events with an offset are to be drawn to the right of the route. In other applications, events with an offset are to be drawn to the left. The dynamic segmentation process allows you to control to which side of the route events with offsets are drawn.