- Introduce `RangeDataInserterInterface` as common interface for all range data inserters
- Introduce a minimal `GridInterface` as a base for a common interface for 2D and 3D grids
- Rename `RangeDataInserter2D` to `ProbabilityGridRangeDataInserter2D`
- Move grid generation logic from `Submap2D` to `ActiveSubmaps2D`
- Update proto and configuration structure to mirror the code structure - backwards compatibility is maintained
- Step towards [RFC 0019](https://github.com/googlecartographer/rfcs/blob/master/text/0019-probability-grid-and-submap2d-restructuring.md)
"scan" is better named "node" if it refers to a node in global SLAM.
"penalty factor" is renamed "weight" for consistency with other similar options.
"scans_per_accumulation" is renamed "num_accumulated_range_data" to match the code and since the accumulated data is not called "scan".
This replaces the scaled covariances derived from the Ceres
scan matcher by directly configurable weights. Using covariances
did not provide the expected benefit, and replacing the scaling
matrix by two values will allow a faster evaluation of the cost
function in the future.
Kevin Daun
Wolfgang Hess
Holger Rapp
Damon Kohler
Damon Kohler