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
ADS-B was a live table and nothing else: an aircraft was overhead for four
minutes and then gone, with nothing kept. Now everything heard goes into
adsb_<time>.jsonl as it arrives -- one object per frame, the raw hex beside
what was read out of it, flushed per line because a listening session ends
with control-C -- with a readable report beside it.
flights.py asks who the aircraft are: adsbdb for the airframe and the
route, hexdb behind it, cached for a month. What needs no website is
answered without one, because the ICAO address block says which country
registered the aircraft and the first three letters of an airline callsign
are its designator. Nothing but the address and the callsign heard on the
air is ever sent.
bandsaunter flights [LOG...] --out sky.gif
reads a log back and draws the evening as a map with the clock running.
Every frame is a moment: each aircraft is where it actually was then,
interpolated between the position reports either side of it and
dead-reckoned from its last speed and heading between them, and dropped
rather than guessed at once it has not been heard for --stale seconds.
The GIF is written here -- palette, LZW, frame differencing against a
transparent index -- so nothing but numpy is needed; ffmpeg writes an MP4
where it happens to be installed, and .png draws the whole evening at once.
The decoder needed 6.3 s to read a second of sky, so a live capture was
losing six frames in seven. Reading the bits off a running total instead
of summing each window takes that to 0.6 s, with identical output.
--simulate flies six aircraft that are not there past a receiver that is
not there, through the real encoder, the real checksum and the real
decoder, so all of this can be tried without an aerial.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016PsWPTweCT6pwxKngvVxcg
