Weighting functions

C/C++

void sdp_weighting_briggs(const sdp_Mem *uvw, const sdp_Mem *freq_hz, double max_abs_uv, const double robust_param, sdp_Mem *weight_grid_uv, sdp_Mem *input_weights, sdp_Mem *output_weights, sdp_Error *status)

Calculate the number of hits per UV cell and use the inverse of this as the weight.

Array dimensions are as follows, from slowest to fastest varying:

  • uvw is 3D and real-valued, with shape:

    • [ num_times, num_baselines, 3 ]

  • freq_hz is 1D and real-valued, with shape:

    • [ num_channels ]

  • grid_uv is 2D and real-valued (should be zero-initialised), with shape:

    • [ num_cells_v, num_cells_u ]

  • weights is 4D and real-valued, with shape:

    • [ num_times, num_baselines, num_channels, num_pols ]

Parameters:

  • uvw – Baseline (u,v,w) coordinates, in metres. Dimensions as above.

  • freq_hz – Channel frequencies, in Hz. Dimensions as above.

  • max_abs_uv – Maximum absolute value of UV coordinates in wavelength units.

  • weight_grid_uv – Output number of hits per grid cell. Dimensions as above.

  • input_weights – Input weights for the visibilities. Dimensions as above.

  • output_weights – Output of the function including the weights for each grid cell. Dimensions as above.

  • weighting_type – Weighting type defined by the user for matching the uv function. Enum Type.

  • robust_param – Input parameter by the user to determine robustness of the weighting. Integer value between -2 and 2.

  • status – Error status.

void sdp_weighting_uniform(const sdp_Mem *uvw, const sdp_Mem *freq_hz, double max_abs_uv, sdp_Mem *weight_grid_uv, sdp_Mem *input_weights, sdp_Mem *output_weights, sdp_Error *status)

Python

ska_sdp_func.visibility.weighting.get_uv_range(uvw, freq_hz)

Calculate uv-range in wavelength units given UVW-coordinates and frequency array.

Parameters:

  • uvw (numpy.ndarray) – List of UVW coordinates in metres, real-valued. Dimensions are [num_times, num_baselines, 3]

  • freq_hz (numpy.ndarray) – List of frequencies in Hz, real-valued. Dimension is [num_channels]

Returns max_abs_uv:

Maximum absolute value of UV coordinates in wavelength units, real-valued

ska_sdp_func.visibility.weighting.uniform_weights(uvw, freq_hz, max_abs_uv, grid_uv, input_weights, output_weights)

Calculate the number of hits per UV cell and use the inverse of this as the weight.

Parameters:

  • uvw (numpy.ndarray) – List of UVW coordinates in metres, real-valued. Dimensions are [num_times, num_baselines, 3]

  • freq_hz (numpy.ndarray) – List of frequencies in Hz, real-valued. Dimension is [num_channels]

  • max_abs_uv (float) – Maximum absolute value of UV coordinates in wavelength units, real-valued.

  • grid_uv (numpy.ndarray) – A initially zero-valued 2D UV grid array. Returns the number of hits per UV cell.

  • weights (numpy.ndarray) – A real-valued 4D array, returns the weights. Dimensions are [num_times, num_baselines, num_channels, num_pols]