Function pio_geo_extract 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_geo_extract(
    net: *const PioNetwork,
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut c_char

Extract a network’s coordinates as the canonical GeoJSON layer: one point per located bus, one route per routed branch. Free the returned string with pio_string_free. Returns NULL (with a message) when the network carries no coordinates.