ENH: Improve multi-variable drag compatibility, regular-grid handling, and related tests/docs

docs/user/function.rst

@@ -90,9 +90,13 @@ plotted as follows:
 
 .. important::
 
-    The ``Function`` class only supports interpolation ``shepard`` and \
-    extrapolation ``natural`` for datasets higher than one dimension (more than \
-    one input). 
+    For datasets higher than one dimension (more than one input), the
+    ``Function`` class supports interpolation ``linear``, ``shepard``, ``rbf``
+    and ``regular_grid``.
+
+    The ``regular_grid`` interpolation requires a complete Cartesian grid and
+    must be provided as ``(axes, grid_data)``. See the ``Function`` API
+    documentation for details.
 
 CSV File
 ^^^^^^^^
@@ -183,7 +187,7 @@ In this section we are going to delve deeper on ``Function`` creation and its pa
 - source: the ``Function`` data source. We have explored this parameter in the section above;
 - inputs: a list of strings containing each input variable name. If the source only has one input, may be abbreviated as a string (e.g. "speed (m/s)");
 - outputs: a list of strings containing each output variable name. If the source only has one output, may be abbreviated as a string (e.g. "total energy (J)");
-- interpolation: a string that is the interpolation method to be used if the source is a dataset. Defaults to ``spline``;
+- interpolation: a string that is the interpolation method to be used if the source is a dataset. For N-D datasets, supported options are ``linear``, ``shepard``, ``rbf`` and ``regular_grid``. Defaults to ``spline`` for 1-D and ``shepard`` for N-D datasets;
 - extrapolation: a string that is the extrapolation method to be used if the source is a dataset. Defaults to ``constant``;
 - title: the title to be shown in the plots.
 

docs/user/rocket/generic_surface.rst

@@ -243,16 +243,17 @@ independent variables:
 - ``beta``: Side slip angle.
 - ``mach``: Mach number.
 - ``reynolds``: Reynolds number.
-- ``q``: Pitch rate.
-- ``r``: Yaw rate.
-- ``p``: Roll rate.
+- ``pitch_rate``: Pitch rate.
+- ``yaw_rate``: Yaw rate.
+- ``roll_rate``: Roll rate.
 
 The last column must be the coefficient value, and must contain a header, 
 though the header name can be anything.
 
 .. important::
    Not all columns need to be present in the file, but the columns that are
-   present must be named, **and ordered**, as described above.
+   present must be correctly named as described above. Independent variable
+   columns can be in any order.
 
 An example of a ``.csv`` file is shown below:
 

rocketpy/plots/rocket_plots.py

@@ -104,20 +104,26 @@ def drag_curves(self, *, filename=None):
         """
 
         try:
-            x_power_drag_on = self.rocket.power_on_drag.x_array
-            y_power_drag_on = self.rocket.power_on_drag.y_array
+            x_power_drag_on = self.rocket.power_on_drag_by_mach.x_array
+            y_power_drag_on = self.rocket.power_on_drag_by_mach.y_array
         except AttributeError:
             x_power_drag_on = np.linspace(0, 2, 50)
             y_power_drag_on = np.array(
-                [self.rocket.power_on_drag.source(x) for x in x_power_drag_on]
+                [
+                    self.rocket.power_on_drag_by_mach.get_value_opt(x)
+                    for x in x_power_drag_on
+                ]
             )
         try:
-            x_power_drag_off = self.rocket.power_off_drag.x_array
-            y_power_drag_off = self.rocket.power_off_drag.y_array
+            x_power_drag_off = self.rocket.power_off_drag_by_mach.x_array
+            y_power_drag_off = self.rocket.power_off_drag_by_mach.y_array
         except AttributeError:
             x_power_drag_off = np.linspace(0, 2, 50)
             y_power_drag_off = np.array(
-                [self.rocket.power_off_drag.source(x) for x in x_power_drag_off]
+                [
+                    self.rocket.power_off_drag_by_mach.get_value_opt(x)
+                    for x in x_power_drag_off
+                ]
             )
 
         _, ax = plt.subplots()

rocketpy/rocket/aero_surface/generic_surface.py

@@ -1,11 +1,11 @@
 import copy
-import csv
 import math
 
 import numpy as np
 
 from rocketpy.mathutils import Function
 from rocketpy.mathutils.vector_matrix import Matrix, Vector
+from rocketpy.tools import load_generic_surface_csv
 
 
 class GenericSurface:
@@ -32,7 +32,8 @@ def __init__(
         angle of attack, angle of sideslip, Mach number, Reynolds number,
         pitch rate, yaw rate and roll rate. For CSV files, the header must
         contain at least one of the following: "alpha", "beta", "mach",
-        "reynolds", "pitch_rate", "yaw_rate" and "roll_rate".
+        "reynolds", "pitch_rate", "yaw_rate" and "roll_rate". The
+        independent variable columns can be provided in any order.
 
         See Also
         --------
@@ -327,7 +328,7 @@ def _process_input(self, input_data, coeff_name):
         """
         if isinstance(input_data, str):
             # Input is assumed to be a file path to a CSV
-            return self.__load_csv(input_data, coeff_name)
+            return load_generic_surface_csv(input_data, coeff_name)
         elif isinstance(input_data, Function):
             if input_data.__dom_dim__ != 7:
                 raise ValueError(
@@ -342,7 +343,21 @@ def _process_input(self, input_data, coeff_name):
                     f"{coeff_name} function must have 7 input arguments"
                     " (alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate)."
                 )
-            return input_data
+            return Function(
+                input_data,
+                [
+                    "alpha",
+                    "beta",
+                    "mach",
+                    "reynolds",
+                    "pitch_rate",
+                    "yaw_rate",
+                    "roll_rate",
+                ],
+                [coeff_name],
+                interpolation="linear",
+                extrapolation="natural",
+            )
         elif input_data == 0:
             return Function(
                 lambda alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate: 0,
@@ -364,82 +379,3 @@ def _process_input(self, input_data, coeff_name):
                 f"Invalid input for {coeff_name}: must be a CSV file path"
                 " or a callable."
             )
-
-    def __load_csv(self, file_path, coeff_name):
-        """Load a CSV file and create a Function object with the correct number
-        of arguments. The CSV file must have a header that specifies the
-        independent variables that are used.
-
-        Parameters
-        ----------
-        file_path : str
-            Path to the CSV file.
-        coeff_name : str
-            Name of the coefficient being processed.
-
-        Returns
-        -------
-        Function
-            Function object with 7 input arguments (alpha, beta, mach, reynolds,
-            pitch_rate, yaw_rate, roll_rate).
-        """
-        try:
-            with open(file_path, mode="r") as file:
-                reader = csv.reader(file)
-                header = next(reader)
-        except (FileNotFoundError, IOError) as e:
-            raise ValueError(f"Error reading {coeff_name} CSV file: {e}") from e
-
-        if not header:
-            raise ValueError(f"Invalid or empty CSV file for {coeff_name}.")
-
-        # TODO make header strings flexible (e.g. 'alpha', 'Alpha', 'ALPHA')
-        independent_vars = [
-            "alpha",
-            "beta",
-            "mach",
-            "reynolds",
-            "pitch_rate",
-            "yaw_rate",
-            "roll_rate",
-        ]
-        present_columns = [col for col in independent_vars if col in header]
-
-        # Check that the last column is not an independent variable
-        if header[-1] in independent_vars:
-            raise ValueError(
-                f"Last column in {coeff_name} CSV must be the coefficient"
-                " value, not an independent variable."
-            )
-
-        # Ensure that at least one independent variable is present
-        if not present_columns:
-            raise ValueError(f"No independent variables found in {coeff_name} CSV.")
-
-        # Initialize the CSV-based function
-        csv_func = Function(
-            file_path,
-            interpolation="linear",
-            extrapolation="natural",
-        )
-
-        # Create a mask for the presence of each independent variable
-        # save on self to avoid loss of scope
-        _mask = [1 if col in present_columns else 0 for col in independent_vars]
-
-        # Generate a lambda that applies only the relevant arguments to csv_func
-        def wrapper(alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate):
-            args = [alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate]
-            # Select arguments that correspond to present variables
-            selected_args = [arg for arg, m in zip(args, _mask) if m]
-            return csv_func(*selected_args)
-
-        # Create the interpolation function
-        func = Function(
-            wrapper,
-            independent_vars,
-            [coeff_name],
-            interpolation="linear",
-            extrapolation="natural",
-        )
-        return func

rocketpy/rocket/point_mass_rocket.py

@@ -21,10 +21,16 @@ class PointMassRocket(Rocket):
     center_of_mass_without_motor : float
         Position, in meters, of the rocket's center of mass without motor
         relative to the rocket's coordinate system.
-    power_off_drag : float, callable, array, string, Function
-        Drag coefficient as a function of Mach number when the motor is off.
-    power_on_drag : float, callable, array, string, Function
-        Drag coefficient as a function of Mach number when the motor is on.
+    power_off_drag : int, float, callable, array, string, Function
+        Drag coefficient input when the motor is off. Accepts the same formats
+        as :class:`rocketpy.Rocket`, including 1D (Mach-only) and 7D
+        (alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate)
+        definitions.
+    power_on_drag : int, float, callable, array, string, Function
+        Drag coefficient input when the motor is on. Accepts the same formats
+        as :class:`rocketpy.Rocket`, including 1D (Mach-only) and 7D
+        (alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate)
+        definitions.
 
     Attributes
     ----------
@@ -35,10 +41,16 @@ class PointMassRocket(Rocket):
     center_of_mass_without_motor : float
         Position, in meters, of the rocket's center of mass without motor
         relative to the rocket's coordinate system.
-    power_off_drag : Function
-        Drag coefficient as a function of Mach number when the motor is off.
-    power_on_drag : Function
-        Drag coefficient as a function of Mach number when the motor is on.
+    power_off_drag_7d : Function
+        Drag coefficient function with seven inputs in the order:
+        alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate.
+    power_on_drag_7d : Function
+        Drag coefficient function with seven inputs in the order:
+        alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate.
+    power_off_drag_by_mach : Function
+        Convenience wrapper for power-off drag as a Mach-only function.
+    power_on_drag_by_mach : Function
+        Convenience wrapper for power-on drag as a Mach-only function.
     """
 
     def __init__(