From values to a line.

An isoline connects locations with the same scalar value: pressure, elevation or temperature. We know the values at grid samples, but we need to find where the chosen level passes between them.

Our extractor is CONREC. It adds the arithmetic-mean centre to a cell, splits the square into four triangles and intersects each triangle with the level. This is not the same interpolation model as bilinear marching squares.

Try this: move the contour level through zero. With alternating corner signs, the centre itself lies on the level. A junction can appear; choosing how to walk through it is a different problem from extracting its segments.

A map arrives in pieces.

Web maps receive tiles independently. A contour ending near a tile edge might be unfinished because its neighbour is absent—not because the field ends there.

The tile builder uses one sample of real neighbouring context. A whole cell belongs to the tile containing its top-left sample. If a required sample is unavailable, that cell waits. There is no invented bridge, clipped contour or copied edge value.

More than one way forward.

When a path reaches several eligible continuations, LoopLook can retain alternative versions. They share their earlier history. A later return to an earlier vertex reveals a candidate loop.

Extracting that loop removes its outside tail from that version only. The source segments remain available to other versions. This is the central idea in Professor Ramon Antonio's LoopLook sketch.

A hypothesis, not a guarantee. Branching explores alternatives; it does not make them scientifically correct. The manuscript's expanded deterministic replay comparison recovers the same accepted boundaries on its six original pressure cases. That result does not establish a boundary-recovery advantage for branching.

A loop is not enough.

A geometrically valid ring can still be unsupported by the scalar field or share source edges with competing candidates. The bounded-side convention checks local interior-side evidence for hills and depressions. Unknown or conflicting candidates stay withheld, with their edges retained as residual linework.

Before declared tile coverage is complete, accepted rings are provisional. Even afterward, a closed boundary is not a certificate for its entire interior, a shell/hole interpretation or every critical-level ambiguity.

Less reading.
More experimenting.

Change the arrival order, remove a tile, then restore it. Inspect an amber junction or a candidate boundary to see the engine's actual diagnostics. Export the current geometry—not a pre-rendered animation.

Browser interface · Web Worker computation · existing CONREC and persistent LoopLook engines