BOOST_GEOMETRY_NO_ROBUSTNESS question

[geoneutrino]

geom.h defines BOOST_GEOMETRY_NO_ROBUSTNESS

data analysis by Claude Code (sorry, translated automatically)
"The simplified ocean shapes contains valid geometries
https://osmdata.openstreetmap.de/data/water-polygons.html
When using in tilemaker (original shapefile geometries, no further simplification) at e.g. z5, ~11.922 N / 122.4101 O Philippines it seems that fast_clip creates self intersections
A self-intersecting “kind=ocean” polygon (feat#12, 89 rings, GEOS-invalid) overlaps the area. The GEOS-based renderer cannot fill in its island gaps → it renders it as solid → the landmass disappears. That's exactly your symptom."
Boost is valid and is simple thinks the geometry is ok due to no rubstness

So the architectural question i cannot answer is the reason / necessity for BOOST_GEOMETRY_NO_ROBUSTNESS ?

[geoneutrino]

Missing landmass at z5

vs. zoom 6

[systemed]

BOOST_GEOMETRY_NO_ROBUSTNESS is a bit of a misnomer. Earlier versions of Boost::Geometry internally rescaled coordinates which could result in unwanted behaviour. BOOST_GEOMETRY_NO_ROBUSTNESS turned this off.

More recently (see boostorg/geometry#958) the BOOST_GEOMETRY_NO_ROBUSTNESS mode (i.e. no rescaling) has been standard, so the flag isn't needed with the latest versions of Boost.