CometChart trail: thin tail is the earliest timepoint, thick head is the latest
The trail narrows as it recedes into the past. The marker and label live at the most recent timepoint. Consumers reading left-to-right intuit the story as "how we got to here" — not "where we started".
CometChart visual-encodingfootball-semantics
Context
A comet trail has two plausible directions: thick-end-is-now (the head is the latest point, trail recedes into the past) or thick-end-is-start (trail advances forward in time, current state is the thin tail). Both appear in the wild. Football editorial convention — xG evolution, form trajectories, transfer-market tracking — reads the latest state as the headline and the history as context. The thick end is the reader’s point of focus.
Decision
- Trail segment opacity increases monotonically from earliest → latest timepoint; the thin tail is always the start.
- Marker (filled circle, full opacity) at the latest point.
- Primary label anchored to the latest point.
showTimeLabelsoptionally labels intermediate points, but the head is always the identity cue.
Consequences
- Overlapping trails in dense plots fade in the same direction; z-order is preserved by sorting entities by latest-timepoint x-coordinate.
- Legend entries align with head colours, not tail colours — the identity cue stays on the focal end.
- Reversing the direction (thick-at-start) is not a supported mode; consumers who want that run the entity series in reverse at the data layer.
- Static export serialises the opacity gradient as per-segment strokes, not an SVG gradient, so rasterisers don’t drop the effect.