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DragModel

Drag model of projectile

DragDataPoint dataclass 

DragDataPoint(Mach: float, CD: float)

Drag coefficient at Mach number

BCPoint dataclass 

BCPoint(BC: float, Mach: Optional[float] = None, V: Optional[Union[float, Velocity]] = None)

For multi-bc drag models, designed to sort by Mach ascending

Source code in py_ballisticcalc\drag_model.py 
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def __init__(self,
             BC: float,
             Mach: Optional[float] = None,
             V: Optional[Union[float, Velocity]] = None):

    if BC <= 0:
        raise ValueError('Ballistic coefficient must be positive')

    if Mach and V:
        raise ValueError("You cannot specify both 'Mach' and 'V' at the same time")

    if not Mach and not V:
        raise ValueError("One of 'Mach' and 'V' must be specified")

    self.BC = BC
    self.V = PreferredUnits.velocity(V or 0)
    if V:
        self.Mach = (self.V >> Velocity.MPS) / self._machC()
    elif Mach:
        self.Mach = Mach

DragModel 

DragModel(bc: float, drag_table: DragTableDataType, weight: Union[float, Weight] = 0, diameter: Union[float, Distance] = 0, length: Union[float, Distance] = 0)

:param bc: Ballistic Coefficient of bullet = weight / diameter^2 / i, where weight is in pounds, diameter is in inches, and is the bullet's form factor relative to the selected drag model. :param drag_table: If passed as List of {Mach, CD} dictionaries, this will be converted to a List of DragDataPoints. :param weight: Bullet weight in grains :param diameter: Bullet diameter in inches :param length: Bullet length in inches NOTE: .weight, .diameter, .length are only relevant for computing spin drift

Source code in py_ballisticcalc\drag_model.py 
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def __init__(self, bc: float,
             drag_table: DragTableDataType,
             weight: Union[float, Weight] = 0,
             diameter: Union[float, Distance] = 0,
             length: Union[float, Distance] = 0):

    if len(drag_table) <= 0:
        # TODO: maybe have to require minimum items count, cause few values don't give a valid result
        raise ValueError('Received empty drag table')
    if bc <= 0:
        raise ValueError('Ballistic coefficient must be positive')

    self.drag_table = make_data_points(drag_table)

    self.BC = bc
    self.length = PreferredUnits.length(length)
    self.weight = PreferredUnits.weight(weight)
    self.diameter = PreferredUnits.diameter(diameter)
    if weight > 0 and diameter > 0:
        self.sectional_density = self._get_sectional_density()
        self.form_factor = self._get_form_factor(self.BC)

DragModelMultiBC 

DragModelMultiBC(bc_points: List[BCPoint], drag_table: DragTableDataType, weight: Union[float, Weight] = 0, diameter: Union[float, Distance] = 0, length: Union[float, Distance] = 0) -> DragModel

Compute a drag model based on multiple BCs. If weight and diameter are provided then we set bc=sectional density. Otherwise, we set bc=1 and the drag_table contains final drag terms. :param bc_points: :param drag_table: list of dicts containing drag table data :param weight: Bullet weight in grains :param diameter: Bullet diameter in inches :param length: Bullet length in inches

Source code in py_ballisticcalc\drag_model.py 
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def DragModelMultiBC(bc_points: List[BCPoint],
                     drag_table: DragTableDataType,
                     weight: Union[float, Weight] = 0,
                     diameter: Union[float, Distance] = 0,
                     length: Union[float, Distance] = 0) -> DragModel:
    """
    Compute a drag model based on multiple BCs.
    If weight and diameter are provided then we set bc=sectional density.
    Otherwise, we set bc=1 and the drag_table contains final drag terms.
    :param bc_points:
    :param drag_table: list of dicts containing drag table data
    :param weight: Bullet weight in grains
    :param diameter: Bullet diameter in inches
    :param length: Bullet length in inches
    """
    weight = PreferredUnits.weight(weight)
    diameter = PreferredUnits.diameter(diameter)
    if weight > 0 and diameter > 0:
        bc = sectional_density(weight >> Weight.Grain, diameter >> Distance.Inch)
    else:
        bc = 1.0

    drag_table = make_data_points(drag_table)  # Convert from list of dicts to list of DragDataPoints

    bc_points.sort(key=lambda p: p.Mach)  # Make sure bc_points are sorted for linear interpolation
    bc_interp = linear_interpolation([x.Mach for x in drag_table],
                                     [x.Mach for x in bc_points],
                                     [x.BC / bc for x in bc_points])

    for i, point in enumerate(drag_table):
        point.CD = point.CD / bc_interp[i]
    return DragModel(bc, drag_table, weight, diameter, length)