A first real capture came back as a map spanning 240 degrees north to 20
south, with the aircraft an indistinguishable smudge in one corner. Two
separate faults, one of them mine from the start.
A position is sent as half a position -- an even frame and an odd one --
and the pair only means anything while the aircraft has not moved between
them. The registry kept the last of each forever and paired them
regardless of age, so an even frame from ten minutes ago decoded against
a fresh odd one to a place on the wrong side of the world. Measured: a
pair 300 seconds apart puts the aircraft 2,566 nm from where it is, and
one night's log had it happening to two aircraft in three, with eleven
positions off the planet altogether. A pair is now good for ten seconds,
the answer has to be on Earth, and the aircraft has to have been able to
reach it.
--radius, defaulting to a hundred, frames the picture on the receiver
rather than on whatever was heard, so the scale is the same from one
evening to the next. In the same unit as the speeds. The centre is the
median of everything heard, which a handful of wrong positions cannot
move, or --at LAT,LON says where the aerial is.
--recheck repairs a log recorded before all this: for each aircraft it
keeps the longest run of positions that could describe one aeroplane.
Not a forward walk dropping whatever disagrees with the last position
kept -- that lets one bad fix become the reference, and on the same log
it discarded a fifth of everything, most of it the truth.
Two calibrations came from the recording rather than from taste. The
failures separate cleanly -- a hundred artefacts under a mile, twelve
hundred real errors over fifty, and nothing in between -- because
positions are stamped to the millisecond, so two a thousandth of a second
apart imply thousands of knots across a few yards. Nothing under two
miles is called an error. Afterwards the worst surviving jump is 513 kt.
One rendering bug the tighter frame exposed: an aircraft just off the top
left painted 743,774 pixels of an 844,200-pixel picture, because the dot
at a marker's centre clamped its near edge and left the far one alone, and
numpy reads a negative slice end as counting back from the far side. And
a still of a whole evening was dead-reckoning every aircraft forward to
the final moment, which for a ten-hour log flew 291 of 335 clean off the
picture; a still now draws each where it was last actually heard.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016PsWPTweCT6pwxKngvVxcg
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
