QGIS » QGIS Application

Depending on the zoom level, the -180 / 180 degree grid lines appear / disappear in QGIS.

This is not depending on a certain projection, but seems to be a spatial filter accuracy issues.

Quote from Even Rouault:
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This seems to be an issue with the spatial filter issued to OGR

At the zooms where the lines disappear, there are requests like:

Thread 23 "Thread (pooled)" hit Breakpoint 2, OGR_L_SetSpatialFilterRect
(hLayer=0x7f81180c90a0, dfMinX=-179.79163612932865,
dfMinY=-69.446164378986353, dfMaxX=179.90530755284408,
dfMaxY=78.959077253477474) at ogrlayer.cpp:1223

At the zooms where that work (even when zoomed in), there are like:

Thread 29 "Thread (pooled)" hit Breakpoint 2, OGR_L_SetSpatialFilterRect
(hLayer=0x7f81180c90a0, dfMinX=-180, dfMinY=-90, dfMaxX=180, dfMaxY=90) at
ogrlayer.cpp:1223

I haven't looked at the QGIS code that computes this bounding box, but from my
experience with gdalwarp which has similar challenges, it is tricky to compute
a source bounding box from a target bounding box, because sometimes the
coordinates in the target bounding box do not correspond to a physical point
on Eath, and hence inverse projection fails. So you have to resort to a grid
sampling approach, but that makes you miss the exact boundaries. So probably
that a band-aid fix would be to add some ad-hoc logic, like "if the source SRS
is long/lat, and the computed extent is almost worldwide, then extend it to
full worlwide (or do not emit a spatial filter at all)"
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Attached is a Geopackage file with grid lines for testing.