Feat/cartesian coordinates

[idoaignostics]

Vibe coded with Claude Code to add support for converting cartesian coordinates, e.g. for WSI analysis results.

1. New --cartesian projection mode — linear x,y mapping instead of Mercator, aspect-ratio-preserving
2. --cartesian-extent flag — defines coordinate space bounds, required with --cartesian
3. Metadata round-trip — cartesian mode/extent saved to MBTiles, auto-detected on decode and tile-join
4. Disabled world-wrapping for cartesian mode
5. Used projection->unproject() generically — replaced hardcoded tile2lonlat calls so cartesian projection works through existing pipeline
6. Added tests
7. Updated README

[Copilot]

Pull request overview

Adds a Cartesian coordinate mode to generate and decode vector tiles using raw x/y coordinates (non-geographic), including metadata propagation and new regression tests.

Changes:

• Introduces a new cartesian projection with --cartesian / --cartesian-extent CLI support in tippecanoe, tippecanoe-decode, and tile-join.
• Stores and auto-detects Cartesian mode/extent via MBTiles metadata, and switches decode/join bounding calculations to use the active projection.
• Adds a Makefile test target plus new Cartesian fixtures and updates README documentation.

Reviewed changes

Copilot reviewed 14 out of 18 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
tile.cpp	Avoids world-wrap clipping behavior at z0 when in Cartesian mode.
tile-join.cpp	Switches bbox calculations to projection->unproject, adds Cartesian CLI flags, and attempts metadata auto-detection.
projection.hpp	Declares new cartesian APIs, metadata detection helper, and cartesian globals.
projection.cpp	Implements cartesian project/unproject, projection lookup, and metadata-based cartesian detection.
mbtiles.cpp	Writes cartesian + cartesian_extent metadata when enabled.
main.cpp	Adds Cartesian CLI flags, adjusts bbox wrap logic, and uses projection->unproject for derived bounds/center.
decode.cpp	Adds Cartesian CLI flags and auto-detects Cartesian mode from MBTiles metadata before decoding.
README.md	Documents Cartesian mode and adds decode options; reformats zoom precision table.
Makefile	Adds cartesian-test target and includes it in test / fewer-tests.
tests/cartesian/*.json, *.mbtiles.json	Adds new fixtures/baselines for Cartesian regression tests.
CLAUDE.md	Adds repository guidance for Claude Code.
.idea/*	Adds JetBrains IDE project files.

Files not reviewed (4)

• .idea/.gitignore: Language not supported
• .idea/modules.xml: Language not supported
• .idea/tippecanoe-cartesian.iml: Language not supported
• .idea/vcs.xml: Language not supported

Comments suppressed due to low confidence (1)

tile-join.cpp:655

• These projection->unproject(...) calls happen before set_cartesian_from_metadata(db) is invoked (currently called later in the cleanup loop at ~line 843). If the input tileset is Cartesian and the user relies on metadata auto-detection (no CLI --cartesian), projection will still be the default CRS84 here, and the computed bounds/center will be wrong. Move Cartesian metadata detection earlier (e.g., immediately after opening each input DB / reading metadata.json) before any unproject/bounds calculations, and consider erroring out if inputs mix cartesian/non-cartesian metadata.

		double lat1, lon1, lat2, lon2;
		projection->unproject(r->x, r->y, r->zoom, &lon1, &lat1);
		projection->unproject(r->x + 1, r->y + 1, r->zoom, &lon2, &lat2);
		minlat = min(lat2, minlat);
		minlon = min(lon1, minlon);
		maxlat = max(lat1, maxlat);
		maxlon = max(lon2, maxlon);

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[Copilot]

projection.hpp forward-declares struct sqlite3 but declares set_cartesian_from_metadata(sqlite3 *db). sqlite3 is a typedef from sqlite3.h, so this header will fail to compile in translation units that include projection.hpp without including sqlite3.h first (e.g., write_json.cpp). Use struct sqlite3 * in the signature or add a proper typedef struct sqlite3 sqlite3; forward declaration (or include sqlite3.h).

Suggested change

	void set_cartesian_from_metadata(sqlite3 *db);
	void set_cartesian_from_metadata(struct sqlite3 *db);

[idoaignostics]

Tested with @davidnelvand if it produces visible results, sadly the answer was no. May be revisited in the future.