Hi Even,
I just created an issue: https://issues.qgis.org/issues/19746
and assigned you - if this is ok. Feel free to remove yourself if you
can't work on it.
I also added Richard's related issues for reference.
Thanks a lot in advance!
Andreas
Am 29.08.2018 um 21:58 schrieb Even Rouault:
On mercredi 29 août 2018 21:50:25 CEST Andreas Neumann wrote:
Hi Even,
Thank you very much for the detailed analysis of the spatial filter
issue we have here, that causes the disappearing grid lines.
Would you be interested to work on fixing this issue on our bug fixing
program? This problem annoyed me for quite some time. And it appears on
different world projections.
I might have a look at this, if nobody else more familiar with the relevant
code looks at it. Is there a ticket filed about that ?
Even
Thanks,
Andreas
Am 28.08.2018 um 22:19 schrieb Even Rouault:
Yes, seems restricted to reprojection cases
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)"
Even
With EPSG:4326 it does not seem to happen, but I tried EPSG:3857 and the
-180,180 grid lines do appear and disappear at different zoom levels. I
also confirm this with the Robinson projection with the addition that the
-90, 90 degree latitude lines also appear and disappear.
Calvin
On Tue, Aug 28, 2018 at 3:31 PM, Andreas Neumann <[email protected]>
wrote:
Hi again,
For some time already I noticed that, depending on the zoom level, the
-180 / 180 degree grid lines appear / disappear in QGIS. This is
unrelated
to the EqualEarth projection just discussed and also appears on other
world
projections, like the Robinson projection.
Here is the testfile I used with world (countries) and gridlines:
http://www.carto.net/neumann/temp/gridlines.gpkg
Can you reproduce this behaviour?
Any idea why this happens and how this could be fixed?
Thanks,
Andreas
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