priority_flow.slope_calc_standard

Calculate slopes from a DEM.

Line-by-line translation of Slope_Calc_Standard.R (SlopeCalStan) from the R PriorityFlow package. R uses 1-based indexing; we use 0-based.

Functions

slope_calc_standard(, minslope, maxslope, ...)

Calculate the slopes from a DEM.

Module Contents

priority_flow.slope_calc_standard.slope_calc_standard(dem: numpy.ndarray, direction: numpy.ndarray, dx: float, dy: float, mask: numpy.ndarray | None = None, d4: Tuple[int, int, int, int] = (1, 2, 3, 4), minslope: float = 0, maxslope: float = -1, secondary_th: float = -1, printflag: bool = False) → Dict[str, numpy.ndarray][source]

Calculate the slopes from a DEM.

This function will calculate slopes using standard or upwinding options and apply a range of smoothing options.

Parameters:

  • dem (np.ndarray) – 2D array of elevations in HydroFrame layout.

  • direction (np.ndarray) – 2D array of D4 flow directions for each cell, using the convention encoded in d4.

  • dx (float) – Lateral grid cell resolutions in the x and y directions, respectively.

  • dy (float) – Lateral grid cell resolutions in the x and y directions, respectively.

  • mask (np.ndarray, optional) – 2D mask defining the domain extent to be considered. Cells with value 0 are excluded from slope calculations. If None, the full rectangular domain of dem is used.

  • d4 (tuple of int, optional) – Direction numbering system for the D4 neighbors, given as (down, left, up, right). Defaults to (1, 2, 3, 4) to match the original R implementation.

  • minslope (float, optional) – Minimum absolute slope to enforce on primary-direction slopes. If minslope >= 0, primary slopes with magnitude less than this value are adjusted up to minslope (with sign preserved). Defaults to 0.

  • maxslope (float, optional) – Maximum absolute slope to enforce. If maxslope >= 0, slopes with magnitude greater than this value are limited to ±maxslope. If set to -1, no maximum is applied.

  • secondary_th (float, optional) – Secondary threshold - maximum ratio of |secondary|/|primary| to be enforced. NOTE - this scaling occurs after any max threholds are applied. Currently this is only working for two options: (1) If this is set to -1 no scaling will be applied, (2) If this is set to zero all seconeary slopes will be zero

  • printflag (bool, optional) – If True, print progress information and details about slope limiting and secondary-slope handling.

Notes

River methods:

  • 0: default value, no special treatment for river cells.

  • 1: scale secondary slopes along the river (requires a river mask and a river-specific secondary threshold).

  • 2: apply watershed mean slope to each river reach (requires river mask and subbasins).

  • 3: apply the stream mean slope to each reach (requires river mask and subbasins).

NOTE: The river mask can differ from the rivers used to create the subbasins (for example, using a higher threshold to define subbasins and a lower threshold to define river cells).

Returns:

Dictionary containing:

  • "slopex": 2D array of adjusted x-direction face-centered slopes.

  • "slopey": 2D array of adjusted y-direction face-centered slopes.

  • "direction": the (possibly renumbered) flow-direction array used when constructing primary/secondary masks.

  • "Sinks": 1D array of linear indices (flattened) marking locations where slope signs were flipped to remove sinks.

Return type:

Dict[str, np.ndarray]