@chartdown/measure

Turn georeferenced imagery into Chartdown declarations — so a traced coastline is data a story can attach to, not a wall of coordinates.

GEO="--origin 48.65,-123.75 \
     --georef 1146,2052=47.2690,-122.5517 \
     --georef 1046,478=48.4061,-122.6433 \
     --georef 202,838=48.1490,-123.5670"

npx @chartdown/measure inspect sea.png --invert $GEO
npx @chartdown/measure feature sea.png --invert --mouth 1255,1361 --into 1094,1646 --word cove --id sinclair $GEO
npx @chartdown/measure coast   sea.png --invert --from "68,0mi" --to "0,32.1mi" --id shore $GEO
npx @chartdown/measure island  sea.png --invert --inside 793,2126 --id squaxin $GEO

Each verb prints a declaration you can paste into a document, with its assumptions above it as ; comments.

The verbs

• inspect — what the tool sees before it measures anything: the classification it chose, how much of the frame is water, and the georeference it fitted, including the transform itself and how far each landmark missed. Run it first; a bad georeference is invisible afterwards.
• feature — one inlet, from a mouth and a point inside it. Emits size=, taper=, and a via centerline carrying the channel's width at each control.
• coast — a coastline with the inlets you intend to declare removed, so the shore and the features on it are not drawn twice.
• island — one island's outline from a point inside it, framed as offsets from its anchor.

What it promises

A measurement emits a line that draws. The output is checked the way the renderer will check it — splined with the renderer's own implementation, not a second copy — because two implementations is how a measurement comes to certify a line the renderer then refuses (ADR 0032).

It says what it consumed, not only what it produced. A verb that removes water says how much; a mouth says what share of the sea it enclosed. A control count looks equally reasonable for a good spine and for a deleted one (ADR 0036).

It refuses rather than guesses. A point in water, a point on the mainland, an image too coarse to resolve the island — each is reported with the number you need to fix it in one edit, not measured around.

PNG only, and zero runtime dependencies (ADR 0029).

More

The specification is the source of truth; ADR 0028 explains why measurement is an optional package rather than part of the language. Try Chartdown itself in the playground.

MIT.