Core Fringe Fitting Engine

The core fringe fitting engine provides the main interface through which VLBI fringe fitting is executed. This library provides the abstract base class MHO_FringeFitter which provides the main interface, as well as concrete implementations for single-baseline fringe fitting with or with ionospheric dTEC correction.

MHO_FringeFitter

Class	MHO_FringeFitter
Primary Functionality	Abstract base class for fringe fitter implementation
Key Features	Pure virtual interface for fringe fitting workflow Data store management (parameters, scan data, containers) Visitor pattern support for extensibility Operator toolbox integration

The MHO_FringeFitter class provides the abstract base class interface for all fringe fitters in the HOPS4 framework. It defines the core workflow methods that must be implemented by concrete fitter classes: Configure(), Initialize(), Run(), and Finalize(). The class manages access to various data stores including parameter stores, scan data, and container objects needed for fringe fitting operations.

MHO_BasicFringeFitter

Class	MHO_BasicFringeFitter
Primary Functionality	Basic single-baseline single-polarization-product fringe fitter
Key Features	Implements basic workflow: configure, init, run, finalize Mixed/single sideband detection and processing Coarse fringe search in delay/delay-rate space Peak interpolation over 5x5x5 grid Visitor pattern support

The MHO_BasicFringeFitter class implements the basic fringe fitting algorithm for single-baseline, single-polarization product data. It provides the core functionality for delay and delay-rate space search. Implemented as a coarse fringe search (max bin), followed by a fine peak interpolation step. This fitter includes support for both mixed and single sideband channel processing modes.

MHO_IonosphericFringeFitter

Class	MHO_IonosphericFringeFitter
Primary Functionality	Single-baseline fringe fitter with ionosphere search
Key Features	Extends MHO_BasicFringeFitter functionality dTEC (differential Total Electron Content) search Optional smoothing function support during search Ionospheric covariance calculations

The MHO_IonosphericFringeFitter class extends the basic fringe fitter to include ionospheric dispersion correction capabilities. It performs searches in dTEC/delay/delay-rate space and includes an optional smoothing function step for more robust ionospheric parameter estimation. This fitter is essential for high-precision VLBI observations where ionospheric effects must be properly modeled and corrected. This implementation is a close port of R. Cappalo’s original implementation but has been extended to allow for an arbitrary number of points in the dTEC search space.

MHO_FringeFitterFactory

Class	MHO_FringeFitterFactory
Primary Functionality	Factory for constructing appropriate fringe fitter types
Key Features	Factory pattern implementation Support for different fitter types (Basic, Ionospheric) Extensible for future fitter implementations

The MHO_FringeFitterFactory class implements the factory pattern for constructing the appropriate fringe fitter based on the user’s configuration parameters. It provides a simple mechanism for creating Basic or Ionospheric fitters as needed by the processing pipeline. This design pattern allows for easy extension to support additional fitter types in the future without modification of any of the pre-existing fringe fitter implementations.