Different output from h3-js and postgis using cellToBoundary function about h3-js

[nrabinowitz]

The shapes aren't weird, they're just being rendered poorly. When H3 (and h3-js) outputs shapes that cross the antimeridian, we keep all longitude values within the -180 - 180 range, so you may have some cells that have some western coordinates at longitude 179 and some eastern coordinates at -179. Many maps will render this badly, but from a geographic shape perspective this is correct.

Either PostGIS or ogr2ogr is taking the approach of cutting these cells into multipolygons, with one poly on one side of the antimeridian and one poly on the other. Normally I'd expect to see the dividing line rendered as well, but possibly your renderer expects this input and drops the dividing border. This is a perfectly good rendering solution, but I don't consider it a good generic solution because it gives you two shapes for some cells, instead of one.

Depending on your requirements, you can post-process the h3-js output to render better, either by running it through a tool that can cut it up, or by normalizing the coordinates to extend past -180 and 180. See this fixTransmeridian function for an example of the latter approach.