Time

One layer type, and one thing built on top of it that does not look like it at all.

trip

SELECT vehicle_id AS trip_id,
       lat        AS latitude,
       lon        AS longitude,
       ts         AS time
FROM vehicle_positions
ORDER BY vehicle_id, ts;

Built automatically from a trip id, a time and a position. The points are grouped into paths, sorted by time within each trip, and handed to kepler as an animated Trip layer with a playback timeline.

kepler will not build this one itself: its own heuristic insists on a column literally named id, and real trajectory tables call it vehicle_id, imei or device. So the panel emits the layer configuration explicitly. See Trajectories.

It draws nothing until the clock runs

The image above is a frame from partway through the animation. At the start of the window every trail has zero length, so a paused trip map at t=0 is a blank map. That is not a fault — it is what an animation looks like before it starts.

The same applies to screenshots: npm run docs:shots plays the animation for six seconds before capturing this panel, because otherwise the gallery would show an empty map.

Trail length

The single control that changes the character of the map most. Short reads as a comet moving along the route; long reads as the route drawing itself.

kepler exposes it in the layer panel but does not document it. It is deck.gl's trailLength on TripsLayer, and kepler multiplies what you type by 1,000 before passing it on.

Table columns or GeoJSON

The Trip layer panel option picks between kepler's two shapes. The default, Table columns, keeps one row per GPS ping and with it every column your query returned — so speed, mode and driver stay available for colour, filters and tooltips. GeoJSON folds each trip into a single row carrying only the path: far less data, nothing else survives.

Backed by deck.gl's TripsLayer, plus ScenegraphLayer when a 3D model rides the head of the trip.

Velocity fields run on a clock of their own

A query returning a grid of wind or current vectors produces a Streamlines layer, which traces streamlines through the field — the paths a massless particle would take — and animates a trail along each of them.

It does not use the playback on this page. The lines run on a clock of their own, so they keep moving while the dashboard's timeline sits still, and there is no blank map at the start of a window. They stop by themselves when the panel scrolls out of view or the tab goes to the background, they can be switched off with the layer's Animate knob, and they respect the operating system's reduce motion setting.

What the dashboard's clock does instead is choose the hour. A query carrying a whole forecast puts every hour on the map at once, and the layer draws the latest one the time filter leaves standing — so dragging the timeline walks the forecast rather than replaying one moment of it. Hours already traced are kept, so walking back and forth is free.

Two other differences from a Trip layer: the geometry is computed rather than queried, and re-computed whenever the map settles, so density and on-screen line length stay constant as you zoom; and trail, cycle and density are the layer's own settings.

See Wind and other velocity fields.

Time without animation

A dataset with a time column but no trip id gets a time filter rather than a Trip layer — a histogram with a brush, over whatever layer you are already drawing. That is the right tool for "show me points in this window"; the Trip layer is for "show me things moving".

Both couple to the dashboard, in four different ways, with quite different costs. See Time range sync.