Cache-Invalidierung (Expire) Equal Earth projection (EPSG:8857)

[astridx]

I'm currently taking my first steps with osm2pgsql, Themepark, and the Equal Earth projection (EPSG:8857). In my Lua script, I set themepark:set_option('srid', 8857), and at first glance, it seems to be working correctly. The WITH_PROJ option is enabled (as described [here](https://github.com/osm2pgsql-dev/osm2pgsql?tab=readme-ov-file#using-the-proj-library)).

For importing data, I'm using the following command:

osm2pgsql --output flex --style LUAFILE -d DBNAME DATAFILENAME

However, I’m still unclear on how tile expiration works—specifically, how data tiles are invalidated over time or after changes. I've been looking at this script for guidance: [expire.lua](https://github.com/pnorman/spirit/blob/main/expire.lua).

While using it, I encountered the following error:

themepark.lua:378: Error in 'define_table': Expire only allowed for geometry columns in Web Mercator projection.

From what I can tell, this error is triggered by the following code in osm2pgsql:

osm2pgsql/src/flex-lua-table.cpp

Line 211 in 210fde0

void parse_and_set_expire_options(lua_State *lua_state,

Does this mean tile expiration is strictly limited to the Web Mercator projection, or is there a way to enable it for other projections like Equal Earth (EPSG:8857)?

[pnorman]

The tiles produced are a list of xyz tiles which, by definition, are in web Mercator. There is no universal standard for other projections as they may have a non-square area or the area of the projection may not be well defined.