@Affie and I had a long frustrating conversation to confirm what we already know: That factor data fields need to be updated for DFG 1 milestone. This ticket is the confluence of many other comments including the most recent:

• Dont nest JSON strings in pre JSON structs (FactorDFG) #1118

Context for larger work beyond this issue:

1. [This issue] Add new field to FactorDFG.observFnc, and replace associated old accessors such as @deprecate getObservationFunction(::FactorDFG) getFactorFunction(::FactorCompute).
   TAC

• spike to check no adverse effect on SDK.rs/c
• add new field to FactorDFG.observFnc (side by side with old .data / .fnctype)
  • Also see performance discussion (or Summary level) FactorDFG.observFnc_type::String Investigate splitting factor operational part from 'constant' part of factor #992
• implement getObservationFunction(::FactorDFG)
• deprecate getFactorType use getObservationFunction( DFG or Compute )

2. Move all other FunctionNodeData fields to FactorDFG - Investigate splitting factor operational part from 'constant' part of factor #992
3. Update CCW construction when building FactorCompute - Investigate splitting factor operational part from 'constant' part of factor #992

Additional links from discussion:

• FactorDFG.data refactor concept discussion #1120