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update CalcFactor docs, #934

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24 changes: 14 additions & 10 deletions docs/src/examples/custom_factor_features.md
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Expand Up @@ -12,20 +12,24 @@ The `cfo` object contains the field `.factor::T` which is the type of the user f

`CalcFactor` was introduced in `IncrementalInference v0.20` to consolidate and standardize a variety of features that had previously been diseparate and unwieldy.

!!! tip
Many factors already exists in `IncrementalInference`, `RoME`, and `Caesar`. Please see their `src` directories for more details.
### Factor Metadata
The MM-iSAMv2 algorithm relies on the Kolmogorov-Criteria as well as uncorrelated factor sampling. This means that when generating fresh samples for a factor, those samples should not depend on values of variables in the graph or independent volatile variables. That said, if you have a non-violating reason for using additional data in the factor sampling or residual calculation process, you can do so via the `cf::CalcFactor` interface.

The MM-iSAMv2 algorithm relies on the Kolmogorov-Criteria as well as uncorrelated factor sampling. This means that when generating fresh samples for a factor, those samples should not depend on values of variables in the graph or independent volatile variables. That said, if you are comfortable or have a valid reason for introducing correlation between the factor sampling process with values inside the factor graph then you can do so via the `cfo.CalcFactor` interface.

At present `cfo` contains three main fields:
- `cfo.factor::MyFactor` the factor object as defined in the `struct` definition,
- `cfo.fullvariables`, which can be used for large data blob retrieval such as used in Terrain Relative Navigation (TRN).
At present `cf` contains three main fields:
- `cf.factor::MyFactor` the factor object as defined in the `struct` definition,
- `cf.fullvariables`, which can be used for large data blob retrieval such as used in Terrain Relative Navigation (TRN).
- Also see [Stashing and Caching](@ref section_stash_and_cache)
- `cfo._sampleIdx` is the index of which computational sample is currently being calculated.
- `cf.cache`, which is user controlled via [`preambleCache`](@ref) function, see [Cache Section](@ref section_stash_and_cache).
- `cf.manifold`, for the manifold the factor operates on.
- `cf._sampleIdx` is the index of which computational sample is currently being calculated.

```@docs
IncrementalInference.CalcFactor
```

!!! tip
Many factors already exists in `IncrementalInference`, `RoME`, and `Caesar`. Please see their `src` directories for more details.

!!! note
!!! warning
The old `.specialSampler` framework has been replaced with the standardized `::CalcFactor` interface. See http://www.github.com/JuliaRobotics/IIF.jl/issues/467 for details.

## Partial Factors
Expand Down