Convex Hull Processor

Summary

The Convex Hull Creator Processor can be used to dynamically produce a polygon that represents the smallest region or area that encloses an event record’s geometry. Conceptually, a convex hull is the shape a rubber band would take if it were stretched around an event record’s geometry.

Illustration

Examples

• The convex hull around multipoint geometry event records can be used as an input for dynamic geofencing. Assets that intersect the convex hull can be considered to have intercepted the multipoint feature.
• A convex hull around a polygon feature can be used to simplify the geometry of irregular shapes which may possess a significant number of vertices for processing. This is useful for generalizing shapes and improving storage performance.

Usage notes

• Given a point, the processor will create an equivalent point.
• Given a line with two vertices, the processor will create an equivalent line.
• Given a simple convex polygon or envelope, the processor will create an equivalent geometry.
• Otherwise, given an irregular or concave polygon, the processor will create the smallest convex polygon that contains the event record’s geometry.
• The processor requires the field containing the event record’s geometry be specified. A geometry field name can be specified, or the GEOMETRY tag can be applied to a field in a GeoEvent Definition to identify the geometry field.
• The Geometry Field parameter will show the name of every field from every GeoEvent Definition that has a data type of geometry. When selecting the geometry field by name, choose the name of the correct geometry field that corresponds to the event record’s GeoEvent Definition.
• The processor can be configured to either replace the event record’s geometry with the created convex hull or place the convex hull into a new geometry field using the Replace Geometry parameter. Altering an event record's schema by adding a new field requires GeoEvent Server to create a new GeoEvent Definition. The new GeoEvent Definition will be managed by GeoEvent Server and deleted if changes are made to the processor or the GeoEvent Service in which the processor is used.
• Choosing Yes for the Tag the New Geometry Field as Geometry parameter explicitly tells GeoEvent Server which geometry field should be treated as the event record’s realized geometry for subsequent processing or output.

Parameters

Parameter	Description
Name	A descriptive name for the processor used for reference in GeoEvent Manager.
Processor	The name of the selected processor.
Geometry Field	The name of the geometry field or the GEOMETRY tagged field from the inbound event record the processor will use to calculate the convex hull.
Replace Geometry	Specifies whether to replace the current event record geometry with the geometry of the convex hull. The default is Yes. Yes - The event record geometry will be replaced with the geometry of the convex hull. No - The event record geometry will remain the same. The geometry of the convex hull will be stored in a new geometry field as part of the event record. Altering a GeoEvent’s schema by adding a new field name requires a new GeoEvent Definition.
New Geometry Field Name (Conditional)	The name of the new geometry field where the convex hull geometry will be stored. This property is shown when Replace Geometry is set to No and is hidden when set to Yes.
Tag the New Geometry Field as Geometry (Conditional)	Determines whether the new geometry field created by the processor will be tagged as GEOMETRY. The GEOMETRY tag is used by GeoEvent Server to identify the event record’s realized geometry when multiple geometry fields are present. The default is No. This parameter is shown when Replace Geometry is set to No and is hidden when set to Yes.
New GeoEvent Definition Name (Conditional)	The name assigned to the new GeoEvent Definition. The new GeoEvent Definition will combine the schema of the inbound event record with the additional new geometry field. This parameter is shown when Replace Geometry is set to No and is hidden when set to Yes.

Considerations and limitations

• Consider replacing the existing event record geometry with the geometry representing the convex hull prior to sending the event data to a feature service. Feature services only support one geometry type field, so whichever field has not been tagged as GEOMETRY will be converted and kept as a string.