Observations

Technical part: the observation file#

What follows is for whoever writes these files by hand, generates them or reads them in code. In the editor none of it has to be known.

A recording is a plain JSON file. Nothing in it is a binary blob, an id into a database, or a reference to this site — you can write one by hand, generate one from your own archive, or diff two of them in a code review.

Every excerpt below is read-only, and each knows the format: put the caret inside an object and press Ctrl+Space (⌥+I on a Mac) to list every key that could go there, with what the model says of each.

The observation#

Several observers: the case#

Each observer has a recording of their own, and a recording does not say which case it belongs to: an account stands on its own. What shows them together is the case, which names them: the case.json of an RR0 dossier, which states the case's title, date and classification, and lists everything that happened in it as events. Its events of type sighting are its accounts, each pointing at one observer's recording:

{
  "id": "ChilesWhitted",
  "title": "Chiles et Whitted",
  "time": "1948-07-24 02:45",
  "events": [
    { "type": "event", "eventType": "sighting", "url": "observer-chiles.json" },
    { "type": "event", "eventType": "sighting", "url": "observer-whitted.json" }
  ]
}

Give it to <rr0-sighting src> or to the player, and each observer can be picked from a list. One recording can be given directly, with no case, but a case with one sighting works the same way and names what it shows. Try it with case-chiles-whitted.json (play it).

Saying it in more than one language#

A recording is handed from one reader to another, so every field an author writes can hold one string per language instead of one: description, a shape's or a decor object's title, and a milestone's label and note.

{
  "description": {
    "fr": "Tout le compte rendu de Lonnie Zamora, d'un seul tenant…",
    "en": "Lonnie Zamora's whole account, of a piece…"
  }
}

Keys are language tags as a browser gives them (fr, en, pt-BR), and none of them is required. A plain string stays perfectly valid and means “in whatever language it was written in” — which every recording made before this is. A reader whose languages are none of the ones present gets what the file DOES have rather than an empty field: a missing translation must never turn something the observer said into something they did not.

Which language a reader gets is their browser's, unless the page says otherwise: a lang on the element itself, or on anything around it, is taken first — an article that declares its own language has already stated what language its reader is reading it in. The browser's list is what follows, so declaring one forces a choice without throwing away the others.

The editor shows one language, the reader's own, and writing back touches only that one — so opening a file in the other language and typing is how a translation gets added, and one author cannot delete another's.

What was seen#

timeline.keyframes is a list of { t, shapes }, t in milliseconds from the start. Each shape carries a sourceId — several shapes can share one timeline (the phenomenon, a trailing flame, a second light) — and a shape:

{
  "kind": "oval",
  "bounds": { "x": 0, "y": 0, "width": 0, "height": 0 },
  "color": "#39ff14",
  "angle": 0,
  "transparency": 0,
  "haloScale": 1.5,
  "brightness": 0,
  "blur": 0,
  "selected": false,
  "title": "the phenomenon",
  "angular": { "widthDeg": 1.2, "heightDeg": 0.4 },
  "aim": { "azimuthDeg": 353.6, "altitudeDeg": 0.6 }
}

aim places it, angular sizes it. bounds is those two projected onto the fixed 640×360 canvas at the pose's own heading and field of view, through the recording's own instrument; it is re-derived on load, so a file survives a change of canvas, of field of view, of instrument, or of where the observer was looking. If the pixels and the angles ever disagree, the angles win: moving bounds in a file does nothing while aim is there. A file written by hand can leave bounds out entirely.

timeline.order is the back-to-front paint order, timeline.groups the grouped source ids. Both optional.

Everything around it#

A decor object is stated in metres, like everything that is not the phenomenon:

What it was: interpretations#

A recording states angles, and a body in metres is never part of what was seen. It is a claim about it, and it is tested by standing it in the scene and looking at it from where the observer stood: it casts its shadow, the ground can hide it, and its outline is measured against what the observer said at every instant. An interpretation is shown alone, as the world it claims; asked to compare (the ◌ button, or compare-account on <rr0-sighting>), the player draws everything the observer saw beside it as dashed outlines and lists how far off the direction is and how many times wider and taller each body looks, in red when an observer could not have been that far off.

The observer's own reading goes in the recording, as interpretation. Someone else's reading is not part of the account: it is another sighting, listed in the case (see below). A account whose observer said what it was is drawn in the round, as they said; one that says nothing in metres is drawn as the angles it states. The player offers it and each analyst's interpretation, one at a time.

{
  "interpretation": {
    "title": "A craft standing on its legs",
    "bodies": [{
      "id": "craft",
      "explains": ["ufo-1"],
      "model": { "id": "ellipsoid" },
      "track": [
        { "t": 52000, "eastM": -571.6, "northM": -965.5, "onGround": true,
          "sizeM": { "widthM": 3.36, "lengthM": 3.36, "heightM": 1.73 },
          "appearance": { "color": "#e8e6df", "albedo": 0.7 } },
        { "t": 83000, "azimuthDeg": 195.9, "altitudeDeg": 4.1, "distanceM": 44 }
      ]
    }]
  }
}

Events of the sky#

What happened in the sky while the recording runs, as facts: a laser shot, a rocket launch, a re-entry. Each was there whether anybody saw it or not, so it is neither part of the interpretation, which reads the account, nor decor, which outlasts the observation (a house, a tree). They are stated under skyEvents, at the top of the recording; a recording that put them in its interpretation, as earlier versions did, is still read.

{
  "skyEvents": {
    "beams": [{
      "id": "meudon-paris",
      "path": [
        { "lat": 48.805055, "lng": 2.231171, "altitudeM": 172.5 },
        { "lat": 48.83632, "lng": 2.33702, "altitudeM": 88 }
      ],
      "wavelengthNm": 532,
      "powerW": 10
    }]
  }
}

Another reading: an interpretation is another sighting#

Someone else's reading of an account (an analyst's, an investigator's, a comparison made to test it) is not part of the account: it is another observation, the one that took place as its author holds it. So it is listed in the case like the original, as an event of type sighting, marked as a reading by interpretationOf, and has a recording of its own at url:

{
  "id": "McMinnville1950",
  "events": [
    { "type": "event", "eventType": "sighting", "id": "trent", "title": "Paul Trent", "url": "observer-mcminnville.json" },
    { "type": "event", "eventType": "sighting",
      "interpretationOf": "trent",
      "time": "2013-06",
      "by": [{ "people": "CousynAntoine" }, { "people": "LouangeFrancois" }],
      "title": "A model on a thread under the line",
      "url": "interpretation-mcminnville-2.json" }
  ]
}

The recording at url is a recording like any other. It shares the place, the time and the observer's pose of the account it reads, so that a body placed from the observer, or in metres from where they stood, means the same in both; it draws no shape of its own (an empty timeline); and it holds the bodies in its own interpretation, described above. A body's explains names the shapes of the account.

{
  "version": 1,
  "id": "1950-05-11-TrentPaul-interpretation-2",
  "time": { "year": 1950, "month": 5, "day": 11, "hour": 19, "minute": 45 },
  "utcOffsetHours": -7,
  "place": [{ "value": { "lat": 45.104167, "lng": -123.330556 } }],
  "observerTrack": { "keyframes": [{ "t": 0, "pose": { "lat": 45.104167, "lng": -123.330556, "headingDeg": 41.3, "pitchDeg": 14.85, "fovDeg": 33.4 } }] },
  "tags": ["interpretation"],
  "timeline": { "keyframes": [], "order": [], "groups": [] },
  "interpretation": {
    "title": "A model on a thread under the line",
    "bodies": [{
      "id": "model",
      "explains": ["ufo-1"],
      "model": { "id": "disc" },
      "track": [
        { "t": 0, "eastM": -52, "northM": 118, "altitudeAboveGroundM": 7.5,
          "sizeM": { "widthM": 0.3, "lengthM": 0.3, "heightM": 0.1 } }
      ]
    }]
  }
}

The player lists the case's observers from the events with no interpretationOf and offers each reading beside the account it names, one at a time (the ◌ button measures it against the account). A recording standing alone has no reading but its own interpretation. The older form, an event of type interpretation naming the recording in sighting with its bodies inline or in a file at url, is still read. The editor opens a case: its picker above the render lists the accounts and the readings, each opening as the recording it is, with a button to add a reading (a new recording that shares the account's place, time and pose, and an event for it), one to delete it, and one to export the case and every recording added or changed as a zip. Try it with case-mcminnville.json (play it, edit it).

The weather, and its clouds#

A weather keyframe states the sky's conditions at one moment of the recording's clock; between two keyframes every number is blended, and precipitation type and storm are held. It carries:

Each layer of cloudLayers is a deck of clouds at a real height, and stays itself from one keyframe to the next:

An individual cloud in instances is one cloud of its layer that the file places exactly, because the account did: the one the phenomenon went behind, the one that was there and nowhere else. It is drawn as one of its layer's own — the same texture, the same threshold — told apart from its neighbours by nothing but where it stands and how big it is, and it stands even when the layer's coverage is nought. It rides the layer's wind like the rest, and it hides a phenomenon it passes in front of.

{
  "weather": {
    "cloudLayers": [
      {
        "id": "low", "type": "cumulus",
        "baseM": 1500, "thicknessM": 800,
        "coverage": 0.55, "sizeM": 1400, "density": 1, "darkness": 0.15,
        "instances": [
          { "id": "the-one", "eastM": 0, "northM": 4200,
            "baseM": 1500, "thicknessM": 800,
            "widthM": 1900, "depthM": 1300, "rotationDeg": 12, "density": 1 }
        ]
      },
      { "id": "high", "type": "cirrus", "baseM": 8000, "thicknessM": 400,
        "coverage": 0.2, "sizeM": 2200, "density": 0.35, "iceCrystalAlignment": 0.65 }
    ],
    "precipitationType": "none", "precipitationIntensity": 0,
    "windDirectionDeg": 90, "windSpeed": 5, "storm": false
  }
}

A recording whose weather was looked up (it has a weatherSource) holds the record's answer, not a link to it: ERA5 gives the low, middle and high bands as three layers named record-low, record-mid and record-high, the low base estimated from the spread between temperature and dew point, the other two at 3 500 m and 8 000 m. Their type is unknown (cirrus for the high one), their size and density are drawing assumptions: a reanalysis knows how much of each band was covered, not what the clouds looked like. Ask the record again from the editor and the layers are rewritten; edit a layer by hand and the recording becomes the author's, the source dropped.

Where each value comes from#

Any value in a recording can be written bare, or wrapped with where it came from:

{
  "durationSeconds": {
    "value": 15,
    "basis": "derived",
    "rationale": "13 to 18 s in the investigator's synthesis; the middle taken"
  }
}

basis is stated (the observer said it, and what a bare value means), derived (worked out from what they said plus something checkable: a road's width, a map, a measured drawing; rationale gives the working) or assumed (chosen so the reconstruction has a value at all, on nothing the observer said). The list of assumed values is the list of what to go back to the observer or the file for, which is why it is worth writing even when nothing else is.

Checking a file#

The format is also published as a JSON Schema, generated from the same types as the player: every key it knows, what each may hold, and the words a closed list accepts. A misspelt key or an unknown value fails it. It says nothing about what may be left out, which is a question of meaning this page answers. To see the result, open the file in the player, from a link, or from your disk with the pictures and models it names. The player checks it the same way on loading, and says what it could not play as written behind a ⚠ over the picture: a key nothing reads, a word outside its list, and what it had to make up because a shape's first keyframe left it out (a field held from the keyframe before is the rule above, not a problem).

A whole file#

The smallest recording that still states something — one silent oval crossing the sky over twelve seconds, on a real date at a real place. Everything else in the format is optional, and everything below is doing work:

{
  "version": 1,
  "description": "The smallest recording that still states something: one silent orange oval, a degree and a half wide, crossing the south-western sky from left to right over twelve seconds.",
  "time": { "year": 2024, "month": 8, "day": 12, "hour": 22, "minute": 30 },
  "durationSeconds": 12,
  "utcOffsetHours": 2,
  "place": [{ "lat": 45.19, "lng": 5.72, "name": "Grenoble, Isère, France" }],
  "timeline": {
    "keyframes": [
      {
        "t": 0,
        "shapes": [
          {
            "sourceId": "ufo-1",
            "shape": {
              "kind": "oval",
              "bounds": { "x": 150, "y": 150, "width": 10, "height": 3 },
              "angular": { "widthDeg": 1.6, "heightDeg": 0.5 },
              "color": "#ff8c1a",
              "angle": 0,
              "transparency": 0,
              "haloScale": 1.2,
              "selected": false
            }
          }
        ]
      },
      {
        "t": 12000,
        "shapes": [
          {
            "sourceId": "ufo-1",
            "shape": {
              "kind": "oval",
              "bounds": { "x": 480, "y": 130, "width": 10, "height": 3 },
              "angular": { "widthDeg": 1.6, "heightDeg": 0.5 },
              "color": "#ff8c1a",
              "angle": 0,
              "transparency": 0,
              "haloScale": 1.2,
              "selected": false
            }
          }
        ]
      }
    ]
  },
  "observerTrack": {
    "keyframes": [
      {
        "t": 0,
        "pose": { "lat": 45.19, "lng": 5.72, "elevationM": 0, "headingDeg": 215, "pitchDeg": 20, "fovDeg": 60 }
      }
    ]
  },
  "soundTrack": { "keyframes": [{ "t": 0, "sound": { "kind": "none", "volume": 0, "pitchHz": 100 } }] }
}

To change it and see it play, paste it into the editor, which completes on every key the format has, offers the words each one accepts, and says what the model says about it.

It is /demo-data/example-minimal.json on this site, so you can fetch it, and play it before changing anything. Note that angular and bounds both appear: the angle is what the file MEANS, and the pixels are re-derived from it on load — write the angle, and let a wrong guess at the pixels be corrected for you.

Larger ones to read#

Every demo on this site is a plain file you can open. These four are the ones worth reading to see how a real recording is put together:

Four rules that decide what a file means#

• Discrete fields are held, continuous ones are blended. A shape left out of a later keyframe stays as it was, and so does any field a keyframe leaves out of a shape it does restate: a keyframe that only gives a new aim moves the shape and keeps everything else (restating bounds without aim or angular is taken as moving it by its pixels); one whose first keyframe is at five seconds is already painted, in that state, from zero. To make something stop being visible, keyframe it at transparency: 1.
• Angles only. No real size and no real distance is stored anywhere. Metres are derived, as inequalities, from what the phenomenon was stated to pass behind or in front of (decor[].occludesSourceIds).
• Declared outranks deduced. occludesSourceIds records statements by the observer. Nothing in this format can deduce them: it describes an appearance on a field of view, not a position in space.
• Absent is not zero. No sound track means nobody was asked; kind: "none" means the observer reported hearing nothing. The same distinction runs through the weather and the ice cloud.

This page is the reference for the format. The reasoning behind each field is in the doc comments of its type, which the excerpts above complete with, and in the source.

Components#

Three of the standard elements are about an observation: the scene it is replayed in, the player that shows it, and the editor that describes it. The editor of a case and the editor of an interview have their own sections, on the pages about those.

Standard, and that is the whole design#

These are five Web Components — the browser's own standard for a custom element, not a component of anybody's framework. What follows from that is worth spelling out, because it is why the tool can be handed to you at all:

• They work in any page. A static site, WordPress, a React or Vue app, a wiki, a hand-written HTML file. They are elements; a page that can hold a <video> can hold these.
• Nothing to build. No bundler, no compilation step, no configuration in your project. The module registers its element on import and the browser does the rest.
• Nothing to keep up with. There is no framework version to match, so they cannot be made obsolete by somebody else's major release.
• Their insides are their own. Each carries its markup and its styles in a shadow root, so your page's CSS cannot break them and they cannot break your page.

They compose in one line: both <rr0-sighting> and <rr0-sighting-editor> hold an <rr0-scene>, and the scene holds the playback layer — the timeline, the controls, the pointer's own canvas. So everything the scene answers to is available in all three — through .scene and .scene.ufoElement from the outermost, since the composition lives in a shadow root.

What each one is for#

• <rr0-scene> — the phenomenon in the world around it. The shape an observer drew, its colour and halo and movement, standing in the real sky, horizon, weather and ground of a stated date, hour and place — hidden by what stood in front of it. Useful on its own too, for a sky with nothing in it at all.
• <rr0-sighting> — the account, to watch. A scene plus who is testifying, the observation's own metadata, its credits, and the lines that let a reader take it elsewhere. This is what a published sighting looks like.
• <rr0-sighting-editor> — the account, to reconstruct. Everything above plus the authoring toolbar: describe an observation, or correct one.
• <rr0-case-editor> — a case, to assemble. Holds a <rr0-sighting-editor> and gives it one recording of a case.json at a time: the observers' accounts and the readings of them. It adds, selects and deletes them, and exports the case.
• <rr0-date-input> — a date, with its precision. A picker for a full instant, a text for anything less (EDTF), and how sure it is. The editors use it for an observation's start and end and for a case's date; it tells what it holds by a datechange event.

How they fit together#

You never write the nesting. Each element builds the one below it inside its own shadow root, so what your page contains is a single tag:

<rr0-sighting>           who is testifying, the metadata panel, the embed lines
└─ <rr0-scene>           the real sky, horizon, weather and decor, the phenomenon, playback

<rr0-sighting-editor>    the eight authoring panels
└─ <rr0-scene>           a scene, not a sighting: an editor has its own toolbar

Which is why one script tag brings the ones underneath with it:

So a page showing a sighting and, further down, a bare sky of its own needs one script and two tags — the second element is already registered.

A composition can be reached into, one property at a time:

const sighting = document.querySelector("rr0-sighting")
sighting.scene                    // the <rr0-scene> it composes
sighting.scene.ufoElement         // and the playback layer under that
sighting.scene.ufoElement.play()  // so playback is two properties away

<rr0-sighting-editor> keeps its own composition to itself: what it offers a page is the recording — sightingData — and the event saying it changed.

Which one you want#

They are not variants of one bundle: each is self-contained, so load only the one you need. All three carry Three.js and a star catalogue, which is what a real sky costs.

Putting one on a page is two lines.

Putting one in your application#

After npm install @rr0/ufoathome:

import "@rr0/ufoathome/scene"    // registers <rr0-scene>
import "@rr0/ufoathome/sighting" // registers <rr0-sighting>
import "@rr0/ufoathome/editor"   // registers <rr0-sighting-editor>

Or copy the contents of the package's dist-embed* directories onto your own server and point the <script src> there. Each module references its own assets — the star catalogue, the weather audio — relative to itself, so it keeps working from any path; just keep each bundle's files together. Nothing then depends on this site at all.

Language#

Every label is translated by detection, with no picker: the page's own declared language first — the nearest lang attribute, so <html lang="fr"> gets French labels — then the browser's own preferences, then English. A page that declares nothing falls through to the browser exactly as before.

<rr0-sighting>#

The standard sighting view

The default for a real sighting, one observer or several. It composes an <rr0-scene> and adds the toolbar: who is testifying, and the i panel with the observation's own metadata and its credits, and a share button: the link that replays it, and its embed lines.

<rr0-sighting src="sighting.json"></rr0-sighting>
<rr0-sighting src="case.json"></rr0-sighting>  <!-- a case, and all its observers -->

A recording that names no observer gets no “account by” line at all, which is the accurate thing to say of a sky set up to show a halo.

Every observer's recording is fetched as soon as the list is known, so picking another one is immediate. The list names each by its title, else first names and last name, else id; one that names nobody is numbered by its place in the list.

The i panel opens as a popover, which Escape or a click outside closes (a click outside only, on a browser without popovers). It states the case, the date, the place, the account and the tags; date, place and tags leave it while the show-labels strip already states them. The date is on the observer's own clock (utcOffsetHours, or one approximated from the longitude), not the reader's. The version at its foot opens this observation in the editor. The description leaves it too while the chips show: it is in their Summary box, opened with a click.

The Share button, among the player's own, opens one dialog giving the link or the embed code (the code in an editor that wraps its lines and can be edited), for the player or for the editor, with the options of the sharing page each offered as the player is. The embed code loads the element from wherever this copy of it was itself loaded, so a snippet copied from a local or staging copy points back at that copy.

What it fires

Putting it in your page

<script type="module" src="https://ufoathome.org/lib/rr0-sighting.mjs"></script>
<rr0-sighting src="sighting.json"></rr0-sighting>

sighting.json is a sighting file. Or, after npm install @rr0/ufoathome: import "@rr0/ufoathome/sighting". The bundle is 249 KB gzipped and registers the tag itself — nothing else to call. The overview above says what else that involves, and sharing an observation has the whole example, to try and to copy.

<rr0-scene>#

The phenomenon, the sky and the ground

The shape an observer drew, standing in the real sky, horizon, weather and ground of the recording's own date, hour and place, and hidden by whatever stood in front of it — with the playback controls under it. This is the element the two others build on.

<rr0-scene src="sighting.json"></rr0-scene>

Hovering it names what is under the pointer — a star with its magnitude and height, a planet, a comet, a building, another observer — and says nothing where the ground hides what you are pointing at.

The © button in its corner lists the credits of what it shows — the imagery under the ground and on the map, the models, the pictures of the place, the sounds. Inside <rr0-sighting> the button is hidden: they are in its i panel.

Playback, on ufoElement

Everything about replaying the recording lives one property down, on the playback layer — scene.ufoElement.play() — the same layer the two other components reach through their own scene.

Those two are the only positive and negative defaults this element has, and the difference is deliberate. A recording's named moments are its own words about itself, so they show wherever they exist; the map costs tile requests to a third party the first time it opens, which is not a page's to spend on a reader's behalf without saying so. Either way the reader keeps both buttons, beside the fullscreen one — a page setting a default is not a page forbidding the opposite.

The toolbar and the corner buttons show only while the pointer is over the picture, playing or paused, or when the keyboard moves the focus onto them. A touch screen, which has no pointer to hover with, keeps them shown.

With the time bar focused, the keys work as on a video site: ← goes back 5 s, → forward 5 s, and Space plays or pauses. Playing or pausing, from a key, the button or a click on the picture, shows its sign for a moment in the middle of the picture.

What it fires

Putting it in your page

<script type="module" src="https://ufoathome.org/lib/rr0-scene.mjs"></script>
<rr0-scene src="sighting.json"></rr0-scene>

sighting.json is a sighting file. Or, after npm install @rr0/ufoathome: import "@rr0/ufoathome/scene". The bundle is 238 KB gzipped and registers the tag itself — nothing else to call. The overview above says what else that involves, and sharing an observation has the whole example, to try and to copy.

<rr0-sighting-editor>#

The editor

Everything above plus the authoring toolbar. Put it on a page where people should be able to describe or correct an observation themselves.

<rr0-sighting-editor></rr0-sighting-editor>
<rr0-sighting-editor src="sighting.json"></rr0-sighting-editor>

Its canvas is an editing surface, so enableClickToPlay is off there: a click selects and drags a shape rather than toggling playback. What the eight groups of its toolbar do is the editor's own page.

What it fires

Putting it in your page

<script type="module" src="https://ufoathome.org/lib/rr0-sighting-editor.mjs"></script>
<rr0-sighting-editor></rr0-sighting-editor>

Or, after npm install @rr0/ufoathome: import "@rr0/ufoathome/editor". The bundle is 293 KB gzipped and registers the tag itself — nothing else to call. The overview above says what else that involves, and sharing an observation has the whole example, to try and to copy.

Sources and choices#

Nothing the tool draws is invented. Each value comes from a named source, read at a stated moment, and where no record exists the interface says so instead of filling the gap.

The principles#

• A source is read only when it is needed. Catalogues are built once into the repository; services are called only for a recording that needs them (a place, a date in their span, a button pressed), and never for a date before their record begins.
• What may disappear is hosted here. Data that a third party could take down or that cannot be read from a browser (orbital elements, 3D models) is copied, reduced, and served from ufoathome.org with its credit, so any page embedding a scene gets it.
• Measured beats modelled, and modelled beats assumed. A brightness is a published observation where one exists; a formula fills in only what nobody measured, and an object with neither is computed but not drawn.
• Every service is swappable. Weather, elevation, imagery, place, time zone, models and drafting go through one registry: the source is a visible choice, with its credit next to it, and a second one can be added without touching the rest.
• The limits are stated. Each source below says where it stops: before 1940 for the weather, before 1957 for satellites, before February 2021 for individual passes.

The sky · The air · Satellites · Aircraft and their trails · Weather · The ground · Place and time · Decor, pictures and sound

The sky

The air

The light of the sky is computed, not drawn: sunlight and moonlight traced through a spherical atmosphere of air, haze and ozone at fifteen wavelengths, then shown as an adapted eye or a camera would. Every input below is a published measurement or model; the two display anchors are the only choices.

Satellites

Two levels. For every date since Sputnik, what the Earth's shadow allowed and how many objects were in orbit. From February 2021, which satellites really crossed the sky, where, and how bright.

Aircraft and their trails

From 2022, the aircraft that were in the observer's sky at the hour of a recording, the air they flew in, and the trail their engines left there. What is drawn is a compatible candidate, never an identification, and an empty sky in the record excludes nothing.

Weather

The ground

Place and time

Decor, pictures and sound

The detail of each choice, with the measurements that settled it, is in the code comments of each source in the repository.