CUSTOM_IN_OUT.md

One class to store them all

To store all the data that accumulates from a variety of sensors, we created the Data class which is located in the Data.h header file. It holds an map of (dynamically sized) vectors that store the sub-elements of a measurement. For example its mean and its variance. The map is indexed by the DataElement enum, which you can find in the Types.h header file.

For each "kind" of measurement, there is a configuration object that initialize a specific data type. These configuration are stored in the Types.cpp. There is another enum DataType, which connects a Data object with it's configuration.

The Data class is also used to store the state variables

Streams of Data

A DataStream is a chronological ordered multimap of Data objects. Multimap, because there can be multiple entries fur the same timestamp. We use double timestamps as keys for this multimap, but round them internally to 1e-3 precision to prevent problems with floating point comparisons.

The DataStream class can be found in DataStream.h.

Sets of Data

Multiple DataStream objects can be stored in an DataSet. Our implementation of this DataSet class is again a map that contains indexed DataStream objects. Each stream has an unique key, but the type of the key depends on the use-case.

SensorDataSet

For measurements, we use DataType enums as Keys because we assume that each sensor is unique and connected to a specific type of data. The resulting SensorDataSet can be found in the SensorDataSet.h header.

StateDataSet

For state variables of the factor graph, there is a separate StateDataSet class in the StateDataSet.h header. Here, we use strings as keys to allow more flexibility.

The StateDataSet is usually used inside our FactorGraph class and internally connected to the Ceres back-end by raw pointers. We created it as a more convenient interface for the optimized variables.