MHO_DelayModel

Purpose

MHO_DelayModel evaluates the station a priori delay-model polynomials for both the reference and remote stations at a given fourfit reference time. It computes the baseline delay, delay rate, and acceleration as the difference between the remote and reference station spline evaluations. Additionally, it calculates reference-station-specific delay and rate quantities (used for populating type-208 records on Mark4 export).

Control File Trigger

This operator is internal and not directly triggerable from the control file. It is instantiated and used by the fringe-fitting core to obtain a priori delay-model values at the fourfit reference time.

Input Data

This class operates on station_coord_type containers for both the reference and remote stations. These containers hold delay-model spline coefficients along with metadata such as model start time, model interval, and station identification.

Algorithm

MHO_DelayModel has no Initialize method; all work occurs in ComputeModel.

Model Computation (``ComputeModel``):

  1. Convert the fourfit reference time from its VEX-format string to a hops_clock time point.

  2. Retrieve the station codes (station_code) for both reference and remote stations from their coordinate containers.

  3. Retrieve and convert the delay-model start times (model_start) and model intervals (model_interval) for both stations.

  4. Calculate the time difference between the fourfit reference time and each station’s model start time, expressed in seconds.

  5. Determine the spline interval index for each station: int = floor(t_diff / t_interval). Clamp the index to [0, N_intervals - 1] and warn if extrapolation is required.

  6. Calculate the offset within the selected interval: t = t_diff - int * t_interval.

  7. Extract the spline coefficient sub-vector for the selected interval from each station’s container.

  8. Evaluate the delay spline polynomial for each station using the coefficients and time offset. For a spline with coefficients \(c_0, c_1, \dots, c_{N-1}\) and time offset \(\Delta t\):

    \[ \begin{align}\begin{aligned}\text{delay} = \sum_{p=0}^{N-1} c_p \, \Delta t^p\\\text{rate} = \sum_{p=1}^{N-1} p \, c_p \, \Delta t^{p-1}\\\text{accel} = \sum_{p=2}^{N-1} p(p-1) \, c_p \, \Delta t^{p-2}\end{aligned}\end{align} \]

  9. Compute the baseline delay, rate, and acceleration as the difference between the remote and reference station values.

  10. For reference-station export quantities (Mark4 I/O), correct the reference delay for clock offset and rate, adjust for the approximate time of wavefront passage, and compute the Doppler factor ref_doppler = 1 - rate_ref. Re-evaluate both station splines at the adjusted time (shifted by the reference delay), then compute fRefDelay, fRefRate (scaled by Doppler), and fRefStationDelay.

Effect on Data

This class does not modify any container data. It reads spline coefficients from station_coord_type containers and computes delay, rate, and acceleration values stored internally. The results are accessible via GetDelay(), GetRate(), and GetAcceleration() getters.