What Crosses

What Crosses

Every field does one of three things.

• mapped — both games have it; it is translated.
• derived — the destination needs it and the source never stored it, so it is computed.
• carried — only one game has it. It goes in the sidecar and comes back on the return trip. See Round Trips.

Field-by-field detail, including why each decision was made, is in docs/mapping.md. This page is the short version.

Province identity is exact

Both games paint one province id per pixel and differ only in how a pixel spells it: Open Doctrines packs it big-endian (#000001 is province 1), GD5 little-endian ((1, 0, 0) is province 1). Verified across every province of every shipped map on both sides — 1248 and 2523 of them — with no exception.

No province is ever renumbered. The two rasters differ by swapping red and blue, and nothing else.

Provinces

	Open Doctrines	GD5
owner, name, claims	✅	✅	mapped
population, ports, fortification	✅	—	carried
minorities, political compass, policies	✅	—	carried
cores	—	✅	carried
terrain, neighbours, centres, coastal	—	✅	derived
industry	resources.json level	factories in buildings	mapped, roughly
garrison	a headcount in armies.json	typed divisions	mapped, roughly

Adjacency and centroids are computed from the province raster when converting to GD5, because Open Doctrines derives both at load and never stores them. The centroid finder handles crescent-shaped provinces, whose average pixel falls outside themselves — otherwise GD5 would draw unit counters in the sea.

Nations

	Open Doctrines	GD5
identity	ISO 3166 alpha-3	the key in nation_data	mapped
name, colour, treasury	✅	✅	mapped
flags	a PNG in the archive	raw 60×40 pixels, base64	mapped
alliance, war	✅	✅	mapped
non-aggression, guarantees	✅	—	carried
leader, adjective, faction, manpower, fuel	—	✅	carried
research	research.json, not yet read by the game	✅	mapped, see below

A GD5 nation's identity is its key in nation_data, not its name field. The two are allowed to disagree, and in GD5's own 1914 scenario two separate nations both call themselves "German Empire".

Crossing to Open Doctrines needs an ISO code, which GD5 does not have. Dragoman uses, in order: a code agreed on an earlier crossing (from the sidecar); a table of 252 pairs generated from Open Doctrines' own maps; or one invented from the name's initials, checked for uniqueness and then recorded so it is reused rather than reinvented.

The sea

The two games disagree about what the sea is. GD5 divides water into provinces, gives them to a nation called Ocean, and sails fleets between them. Open Doctrines does not put provinces in the water at all — its 1914 map has 1247 provinces and every one is land — and moves ships by latitude and longitude over a land/sea mask.

So converting to GD5 grows the water into provinces: seeds on a lattice, displaced by a hash of their own coordinates, snapped to the nearest water, then grown outwards all at once through water only. Each province is the water nearest one seed, so they follow coastlines rather than being laid over them, and none can cross land — the Mediterranean and the Atlantic stay separate. The world map gets 917: one network of 747 that is every ocean joined together, plus 163 lakes.

They are an invention, so their ids go in the sidecar and the return trip deletes exactly them. A sea province you draw in GD5's editor is real and stays. --no-ocean turns the whole thing off.

An unpainted pixel means opposite things

	a pixel with province id 0
Open Doctrines	water. Province coverage is the landmass
GD5	not painted yet. Its painter samples every third pixel, so every province border is blank — 37% of its 1914 scenario

Carried across unchanged, every GD5 provincial border became a sea channel three pixels wide and the continents arrived shot through with water. Gaps are now filled from the nearest province before an Open Doctrines map is written, and the mask of what was filled goes in the sidecar so the return trip restores the borders exactly.

Which meaning a raster carries is decided by counting, not by trusting the source. The two populations are nowhere near each other: GD5's maps run 0.35 to 7.8 on the ratio of sea-province pixels to blank ones; Open Doctrines' all sit at 0.0001.

Research

Open Doctrines stores no research in a map at all. Its tree is built in C++ in Game_Research.cpp and each country's starting nodes come from a hardcoded list of ISO codes.

What both formats carry is the date, and GD5 already knows what to do with one: its get_time_appropriate_research(year) gives each technology a level equal to the number of its introduction years that have passed. Dragoman applies that rule, reading the tech tree out of the GD5 installation being written into — not a copy kept in this library, which would go stale the moment anyone modded a technology.

A nation that arrives with research keeps exactly what it had — a carried node list takes precedence over the date rule.

Going the other way, Dragoman writes research.json into the .odmap, mapping GD5's levelled technologies onto Open Doctrines' named nodes. Open Doctrines does not read that file yet, so today the field is carried and inert; making it take effect is about fifteen lines in the game, written out in docs/research.md. Round trips do not depend on any of this — the exact GD5 table rides in the sidecar and returns intact either way.

Only the numbered ladders are translated (ind, navy, arty, conscript), because only they mean the same thing on both sides. Forts and ports have no GD5 counterpart and are never invented; the branching army nodes sit in mutex groups a prefix would violate. Technologies with a ceiling of 1 — GD5 has five, including basic_factory and dreadnought — are flags rather than scales, and count for the first rung of a ladder rather than the whole of it.

Scripts

See Scripts and Events.