[Qgis-user] Arctic data distortion when crossing the 180° meridian (EPSG:3996 vs EPSG:3857)

[김용운 빙하지권연구본부]

Hello,

I am working with Arctic Ocean datasets in QGIS and would like to ask for advice regarding CRS handling and geometries crossing the 180° meridian.

For Arctic data, I normally use EPSG:3996 (WGS 84 / Arctic Polar Stereographic) as the project CRS. In QGIS Desktop, this works well and produces the expected visualization for tracks and stations (Figure 1).

However, when I try to use these datasets in a web mapping context, I am forced to switch the project CRS to EPSG:3857. With this change, datasets that cross the 180° meridian (anti-meridian) show problematic behavior:
- line features are split and displayed at both sides of the map,
- and in some cases the geometries appear distorted or disconnected (Figures 3 and 5).

The original geometry itself is correct (Figure 4), so the issue seems to be related to CRS transformation and rendering rather than data corruption.

I tested several CRS combinations, and the following produced the closest alignment:
- Project CRS = EPSG:3857
- Layer CRS = EPSG:3996

Nevertheless, the anti-meridian splitting issue remains unresolved. I also tried suggestions found in documentation and online discussions (e.g. reprojection, geometry fixes, alternative basemaps), but none solved the problem fundamentally.

Since many Arctic datasets naturally cross the 180° meridian, I would greatly appreciate advice on:
- best practices for handling Arctic/polar data in QGIS,
- recommended CRS strategies when working near the anti-meridian,
- or preprocessing steps that can prevent line splitting and visual discontinuities.

Thank you very much for your time and any suggestions.

Best regards,


[https://bigfile.kopri.re.kr/readreceipt2.ashx?id=MTQwYzAxNjQtYmI4OS00NWYxLWE5MzQtNTc1OTAyMDdmZDcx]
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