GISStream Service Filter
Limits which dynamic entities are returned from an ArcGIS stream service. Set ArcGISStreamService.filter to an object of this type to apply a server-side filter on observations streamed from an ArcGIS stream service. Spatial or attribute filters (or both) are supported.
Using this server-side filter is useful for limiting how much data is streamed from an ArcGISStreamService and handled in the client application, which can help with application performance and memory efficiency.
A collection of field names that identify the observation values the server should return. This property instructs the service to return a subset of values when pushing observations to the client. Restricting the values returned will limit the amount of memory required to store individual observations and therefore reduce the memory footprint of the application.