v0.4.0 — traffic controls

Traffic controls

DeliverySchema gains a signal point layer carrying the things a vehicle has to stop at: traffic lights, stop and give-way signs, and level crossings. A navigation map that cannot show a junction's lights is missing the one feature at that junction a driver plans around.

Four classes, not the dozen OSM offers, and the line is drawn at things that stop a vehicle. highway=crossing is the notable exclusion — an unsignalised pedestrian crossing appears several times a block, would outnumber every other control by an order of magnitude, and means nothing to a driver at speed. A signalised crossing (crossing=traffic_signals, or crossing:signals=yes) is a set of lights and is kept, which is why the exclusion is a specific test rather than a blanket one.

Emitted from z14 rather than from the schema's minZoom: a set of lights is meaningless on a map of a whole city, and carrying a few thousand points through eight zoom levels that never display one is pure archive weight.

readsNodes is now a decision rather than a constant

DeliverySchema reads the node stream only when it is carrying signals, and includeSignals: false restores the old behaviour exactly — no signal layer, no node decoding.

That flag is the real cost of this change and it is worth stating plainly: node tags live in a packed stream a reader can otherwise skip whole, so wanting any node means decoding tens of millions of entries that are almost all untagged shape points. The cost is per build, not per pack byte — the tiles themselves grow by points with one short attribute, a few thousand in a city against a road network of hundreds of thousands of segments.

geoTileBuilderVersion / geoTileBuilderId

So a tool that bakes an artefact can record which release baked it. Dart cannot read pubspec.yaml at runtime and a compiled executable has none beside it, so the version has to be repeated in code; test/version_test.dart reads the pubspec and compares.

The motivation is a real defect rather than tidiness: map packs in production carry an empty builder string, because the only way to set one was a hand-typed flag that defaulted to nothing. A build recorded as 0.3.0 while 0.4.0 ran would be worse than one recorded as nothing, because it looks like an answer.

Full changelog: https://github.com/gmpassos/geo_tile_builder/blob/master/CHANGELOG.md

v0.3.0

• Areas. Polygons are now produced, from both closed ways and multipolygon
  relations. Verified end to end and on screen: Monaco's harbour basins render
  as basins, not as an inverted fill flooding the tile — which is what a
  winding mistake looks like.
• RingBuilder (new):
  • assemble joins a relation's member ways into closed rings. Members arrive
    in no order and no consistent direction, so fragments are indexed by both
    endpoints, reversed where needed, and chained until a ring closes.
    Fragments that never close are dropped: an unclosed boundary is not an
    area, and regional extracts contain them routinely.
  • orient imposes winding — exterior positive, holes negative in tile
    coordinates — rather than trusting source data, which respects no
    convention.
  • nest attaches each hole to the smallest exterior ring containing it,
    because rings nest (an island in a lake on an island) and choosing the
    largest container punches the hole through the wrong shape. Holes inside
    nothing are dropped rather than guessed at.
  • containsPoint, even–odd ray test.
• TileBuilder:
  • Added a relations pass, run first — a multipolygon's member ways
    usually carry no tags, so which geometry to retain is only knowable once
    the relations are known.
  • Polygons are clipped as rings and re-nested per tile, since clipping can
    remove a hole or cut an area away entirely.
  • Features now carry multiple parts, so one feature can be several disjoint
    areas with their own holes.
• PmTilesWriter: centerZoom is clamped into the zoom range actually
  written.
  • Why: a caller passes the centre of the range it asked for, which need
    not be the range it got. The mismatch produced a header that strict
    readers reject outright — found by the pmtiles oracle, not by inspection.
• TileBuildReport.tiles documents that zero means an empty archive, whose
  empty directory strict readers reject: a failed build, not a small one.
• OpenMapTilesSchema (new): a subset of the OpenMapTiles schema using its own
  layer and field names, so an existing style — Dark Matter, Positron, OSM
  Liberty — renders the output unmodified and degrades over the layers this
  subset omits.
  • Implements transportation, transportation_name, water, waterway,
    building and place.
  • On Monaco it costs 2x the delivery schema (310 kB vs 158 kB), of which
    buildings alone are 112 kB. That is the price of compatibility, now
    measured rather than guessed.
• Point features. TileSchema.node was declared but never called; tagged
  nodes now become point features, which is what place labels are.
  • TileSchema.readsNodes (new) declares whether a schema wants them. Node
    tags live in a packed stream a reader can skip entirely, so a schema
    without labels — DeliverySchema — never pays to decode tens of millions
    of untagged shape points.