Remembered portion of Evidence Grid Map in Local mapping

Our use-case briefly:
Using the Navigation Stack in our application we extract data relative to the Evidence Grid Map from the subgraph “evidence_grid_map.subgraph.json”, in particular data coming from the source “evidence_local_map/isaac.egm_fusion.EvidenceMapFusion/evidential_local_map”.
We have noticed that the component doesn’t keep in memory the entire portion of the map that the robot has explored so far, but only the most recent.

Our questions:

  • What is the policy used to decide what parts to keep in memory? (The most recent ones in terms of time, or the most close to the robot ones)
  • Is there a way to control the policy or to decide how much map is kept in memory?

If I understood your question correctly, EGM only fuses live sensor data for a local map (immediate area around the robot within sensing distance as an occupancy grid) and does not build an occupancy grid map. EGM does not register live occupancy grids into an common coordinate frame to create a global map with history. GMapping or Cartographer are probably more what you’re looking for which register occupancy grids into one coordinate frame and the bundle adjusts them with loop closure to be a consistent, metrically accurate global occupancy grid map.