Tilesets written with --output-format=mlt could not be read back by any of
tippecanoe's own tools, which made MLT a dead end rather than a tile format.
Build the mlt-cpp decoder from the vendored maplibre-tile-spec submodule
alongside the encoder, and convert a decoded MapLibre Tile back into the
equivalent mvt_tile: geometry, feature ids, and property columns. MLT rings
come back explicitly closed, so the repeated final point becomes an MVT
closepath, and the property columns, which are held in an unordered map,
are sorted by name so that the attributes of a decoded tile come out in a
stable order.
Rather than adding an option to each tool, mvt_tile::decode() detects the
encoding and dispatches, so everywhere tippecanoe already reads a vector
tile can read MLT. An MLT tile begins with a varint layer length followed
by a varint layer tag whose only defined value is 1, while an MVT tile is
a protobuf whose only field is the repeated layer field 3, so it begins
with 0x1a followed by a layer length that can never be as short as the one
byte that would be needed to look like an MLT layer tag.
Tile directories also needed a fix: enumerate_dirtiles() recognized .mlt
file names but still recorded .pbf as the extension to read them back
with, so decoding an MLT directory failed to find any of its tiles.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LxhELiLtpUFwrPSWwTYdHG
An MLT property column has one type for the whole layer, while MVT values
are individually typed. Converting each value on its own left the encoder
to reconcile the mismatch, and its fallback for a column holding both
integers and doubles is to encode the whole column as strings, so an
attribute like gdp_md_est in tests/ne_110m_admin_0_countries turned into
values like "904.200000".
Summarize each attribute across the layer first and pick one type that can
hold all of its values, so mixed integer and floating point columns become
doubles. Only columns that mix numbers with strings, or booleans with
numbers, still fall back to strings, which is as close as MLT's typed
columns can get.
Also stop encoding JSON-object-valued attributes as MLT struct columns.
Struct children can only be strings, and a struct column is flattened into
"column name + child name" when it is read back, so an attribute `meta`
holding {"en": "one", "de": "eins"} decoded as separate `metaen` and
`metade` attributes. Nested JSON now stays JSON text, the way MVT
carries it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LxhELiLtpUFwrPSWwTYdHG
Claude