Add csv_write() to fix issue #45

.gitignore

@@ -23,3 +23,6 @@ sphinx/_build/
 # Project
 ORC_VPP_2019.pdf
 dev.py
+
+# exported polars (root only, dat/ holds tracked csv data)
+/*.csv

runVPP.py

@@ -41,5 +41,9 @@
 
 vpp.run()
 vpp.write("results")
+# polar csv for routing software, e.g. OpenCPN (5 deg TWA, 2 kn TWS steps)
+vpp.write_csv(
+    "polar.csv", tws_range=np.arange(4.0, 22.0, 2.0), twa_range=np.arange(30.0, 181.0, 5.0)
+)
 vpp.polar(3, True)
 vpp.SailChart(True)

src/UtilsMod.py

@@ -39,6 +39,53 @@ def json_write(data, fname):
         json.dump(data, json_file, ensure_ascii=False, indent=2, sort_keys=False)
 
 
+def csv_write(VPP, tws_range=None, twa_range=None, fname="polar.csv"):
+    """
+    Export the best boat speed (knots) to a polar csv file (TWA rows, TWS
+    columns, ";" separated), the format read by routing software such as OpenCPN.
+
+    Parameters
+    ----------
+    VPP
+        A VPP (after run) or VPPResults object.
+    tws_range
+        Optional TWS (knots) to write. Default: the TWS of the VPP analysis.
+    twa_range
+        Optional TWA (degrees) to write. Default: the TWA of the VPP analysis.
+    fname
+        Name of the csv file, default "polar.csv".
+
+    If tws_range or twa_range is given, the VPP results are linearly
+    interpolated onto it; points outside the analysed range, or where no sail
+    set can be carried, are written as 0.
+    """
+    if not hasattr(VPP, "store"):
+        raise ValueError("VPP object must have a 'store' attribute to export to csv.")
+    import csv
+
+    # best boat speed over the sail sets, the store already holds knots
+    vpp_tws = np.asarray(VPP.tws_range) / KNOTS_TO_MPS
+    vpp_twa = np.asarray(VPP.twa_range)
+    speed = np.max(np.asarray(VPP.store)[:, :, :, 0], axis=2)
+    tws = vpp_tws if tws_range is None else np.asarray(tws_range, dtype=float)
+    twa = vpp_twa if twa_range is None else np.asarray(twa_range, dtype=float)
+    if tws_range is not None or twa_range is not None:
+        func = RegularGridInterpolator(
+            (vpp_tws, vpp_twa), speed, bounds_error=False, fill_value=0.0
+        )
+        grid = np.stack(np.meshgrid(tws, twa, indexing="ij"), axis=-1)
+        speed = func(grid)
+
+    with open(fname, mode="w", newline="") as file:
+        writer = csv.writer(file, delimiter=";")
+        # header with TWS in knots
+        writer.writerow(["TWA\\TWS"] + [f"{round(ws, 2):g}" for ws in tws])
+        for j, angle in enumerate(twa):
+            writer.writerow(
+                [f"{round(angle, 2):g}"] + [f"{speed[i, j]:.2f}" for i in range(len(tws))]
+            )
+
+
 def build_interp_func(fname, i=1, kind="linear"):
     """
     build interpolation function and returns it in a list

src/VPPMod.py

@@ -9,7 +9,7 @@
 
 from src.AeroMod import AeroMod
 from src.HydroMod import HydroMod
-from src.UtilsMod import KNOTS_TO_MPS, json_write, polar_plot, sail_chart
+from src.UtilsMod import KNOTS_TO_MPS, csv_write, json_write, polar_plot, sail_chart
 from src.YachtMod import Yacht as YachtClass
 
 logger = logging.getLogger(__name__)
@@ -281,6 +281,10 @@ def results(self):
     def write(self, fname):
         json_write(self.results(), fname)
 
+    def write_csv(self, fname="polar.csv", tws_range=None, twa_range=None):
+        """Write the best boat speed to a polar csv file, see UtilsMod.csv_write."""
+        csv_write(self, tws_range=tws_range, twa_range=twa_range, fname=fname)
+
     def polar(self, n=1, save=False, fname="Polars.pdf"):
         polar_plot([self], n, save, fname)
 

tests/test_utils.py

@@ -1,7 +1,10 @@
+from types import SimpleNamespace
+
 import numpy as np
 
 from src.SailMod import Jib, Kite, Main
-from src.UtilsMod import _get_cross
+from src.UtilsMod import KNOTS_TO_MPS, _get_cross, csv_write
+from src.VPPMod import VPP
 from src.YachtMod import Keel, Rudder, Yacht
 
 
@@ -53,3 +56,51 @@ def test_get_cross_pad_is_symmetric():
 
 def test_get_cross_no_pad():
     assert tuple(_get_cross(_cross_store(), 1, pad=0)) == (4, 8)
+
+
+def _fake_vpp():
+    """2 TWS x 3 TWA x 2 sails; the store holds boat speed in knots, TWS in m/s."""
+    store = np.zeros((2, 3, 2, 5))
+    store[:, :, 0, 0] = [[5.0, 6.0, 0.0], [7.0, 8.0, 0.0]]  # jib, not set downwind
+    store[:, :, 1, 0] = [[0.0, 5.5, 6.5], [0.0, 8.5, 9.5]]  # kite
+    return SimpleNamespace(
+        tws_range=np.array([6.0, 10.0]) * KNOTS_TO_MPS,
+        twa_range=np.array([40.0, 90.0, 150.0]),
+        store=store,
+    )
+
+
+def _read_csv(path):
+    rows = [line.split(";") for line in path.read_text().splitlines()]
+    return rows[0], {float(r[0]): [float(v) for v in r[1:]] for r in rows[1:]}
+
+
+def test_csv_write_default_grid(tmp_path):
+    fname = tmp_path / "polar.csv"
+    csv_write(_fake_vpp(), fname=fname)
+    header, rows = _read_csv(fname)
+    assert header == ["TWA\\TWS", "6", "10"]
+    # best sail at each point, in knots (no second unit conversion)
+    assert rows == {40.0: [5.0, 7.0], 90.0: [6.0, 8.5], 150.0: [6.5, 9.5]}
+
+
+def test_csv_write_interpolates_custom_grid(tmp_path):
+    fname = tmp_path / "polar.csv"
+    csv_write(_fake_vpp(), tws_range=[6.0, 8.0, 12.0], twa_range=[40.0, 65.0], fname=fname)
+    header, rows = _read_csv(fname)
+    assert header == ["TWA\\TWS", "6", "8", "12"]
+    assert rows[40.0] == [5.0, 6.0, 0.0]  # 12 kn is outside the analysis: 0
+    assert np.allclose(rows[65.0], [5.5, 6.625, 0.0], atol=0.006)  # halfway 40-90 deg
+
+
+def test_vpp_write_csv(tmp_path):
+    vpp = VPP(Yacht=return_YD41_particulars())
+    vpp.set_analysis(tws_range=np.array([8.0]), twa_range=np.array([45.0, 90.0]))
+    vpp.run()
+    fname = tmp_path / "polar.csv"
+    vpp.write_csv(fname)
+    header, rows = _read_csv(fname)
+    assert header == ["TWA\\TWS", "8"]
+    best = vpp.store[0, :, :, 0].max(axis=1)
+    assert np.allclose([rows[45.0][0], rows[90.0][0]], best, atol=0.006)
+    assert all(v > 0 for r in rows.values() for v in r)