Aircraft, from the menus, on a live board, over a real map

Four things the ADS-B mode was missing, and one it was actively getting
wrong.

The band plan lists 1090 MHz because that is where ADS-B is, so choosing
it from the band plan is the obvious thing to do -- and it records the
bursts as clicks in a WAV file and decodes nothing, silently.  Both the
scanner and the menus now say so, before the sweep starts, and name the
mode that does decode it.  It is not refused: looking at the raw spectrum
is a fair thing to want.

Menu 5, Aircraft (ADS-B), is the whole mode without a command line.  Every
option on one screen with a line saying what it does, ?N for the long
version and the flag it corresponds to, l to listen, m to draw a map from
any log, s to keep the options.  The listening and the drawing moved into
bandsaunter/aircraft.py so the menus and the command line run the same
code.

While it listens the screen is a live board: one line per aircraft in the
order first heard, the counter climbing as frames arrive, height coloured
low warm to high cold with an arrow for climb or descent, the age of the
last report going green to red, and the line removed once nothing has been
heard for --hold seconds, everything below moving up.  The registers are
asked while it runs, so registration, type, operator and route fill
themselves in as the answers arrive.

--speed-unit knots|mph|kph changes the heading of that board, the speed
beside every aircraft on the map and the speeds in the report, and moves
the distances with it so that one picture never carries two different
miles.  The log stays in knots, which is what the aircraft broadcast.

And there is a real map under the flight paths: {z}/{x}/{y} tiles fetched
once, cached in ~/.cache/bandsaunter/tiles, reprojected from Web Mercator
pixel by pixel, inverted and dimmed so the aircraft stay the brightest
thing on the picture.  The PNGs are decoded here -- zlib and the five row
filters from the specification, checked byte for byte against Pillow on
real tiles -- so nothing new is depended on.  Tiles are cached and never
re-fetched, every request says who is asking, and the attribution is drawn
onto the picture, because a GIF travels without its readme.

conftest now fails any test that reaches for a tile server or a register.
It caught four of these on the way in.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016PsWPTweCT6pwxKngvVxcg

tests/test_flightmap.py

@@ -398,3 +398,65 @@ def test_the_picture_is_an_even_number_of_pixels_across(tmp_path):
         view = fm.fit(two_aircraft(), width=width)
         w, h = fm.canvas_size(view)
         assert w % 2 == 0 and h % 2 == 0
+
+
+# ---------------------------------------------------------------------------
+# Speeds in whatever the user reads
+# ---------------------------------------------------------------------------
+
+def _label_text(unit: str, width: int = 700) -> np.ndarray:
+    """Draw one aircraft and hand back the pixels its label was written in."""
+    tracks = [straight(speed=480.0)]
+    view = fm.fit(tracks, width=width)
+    base = fm.background(view, unit=unit)
+    return fm.render_frame(base, view, tracks, tracks[0].first_seen + 120,
+                           unit=unit)
+
+
+def _has_text(frame: np.ndarray, text: str) -> bool:
+    """Whether a string was stamped anywhere in the frame, found by drawing
+    it again and looking for the same pattern."""
+    from bandsaunter.images import GLYPH_H, draw_text, text_width
+
+    stamp = np.zeros((GLYPH_H, max(1, text_width(text))), dtype=np.uint8)
+    draw_text(stamp, 0, 0, text, 1)
+    rows, cols = stamp.shape
+    wanted = stamp.astype(bool)
+    if not wanted.any():
+        return False
+    for y in range(frame.shape[0] - rows):
+        for x in range(frame.shape[1] - cols):
+            patch = frame[y:y + rows, x:x + cols]
+            if np.all(patch[wanted] != fm.BG) and \
+                    np.all(patch[~wanted] == patch[~wanted][0]):
+                return True
+    return False
+
+
+@pytest.mark.parametrize("unit,label", [("knots", "KT"), ("mph", "MPH"),
+                                        ("kph", "KM/H")])
+def test_the_speed_on_the_map_carries_its_unit(unit, label):
+    """A bare 480 beside an aircraft is three different speeds depending on
+    who is reading it."""
+    assert _has_text(_label_text(unit), label)
+
+
+def test_the_number_beside_it_is_converted():
+    assert _has_text(_label_text("knots"), "480KT")
+    assert _has_text(_label_text("mph"), "552MPH")
+    assert _has_text(_label_text("kph"), "889KM/H")
+
+
+@pytest.mark.parametrize("unit,label", [("knots", "NM"), ("mph", "MI"),
+                                        ("kph", "KM")])
+def test_the_scale_bar_uses_the_same_kind_of_mile(unit, label):
+    """Miles an hour beside a scale in nautical miles is two different miles
+    on one picture."""
+    view = fm.fit(two_aircraft(), width=700)
+    assert _has_text(fm.background(view, unit=unit), label)
+
+
+def test_the_animation_takes_the_unit_through_to_the_file(tmp_path):
+    out = fm.animate(two_aircraft(), tmp_path / "mph.png", width=500,
+                     unit="mph")
+    assert out is not None and out.path.is_file()