QGIS » QGIS Application

Been doing some more testing and it looks like it doesn't matter how many layers are in the project.

Even a single layer will do this when the "Render layers in parallel using many CPU cores" option is enabled.

Disabling that option fixes the issue.

Or reducing the number of cores used (on an 8 core Intel CPU i7) to 3 or less seems to reduce the artifacts. But they do appear randomly.

And this is only observed on Windows 7 and 8.1 x64 using the OSGeo4W installer. Haven't tested with standalone builds.

Looks like it doesn't have anything to do with the amount of layers and it's only on Windows (7 and 8.1 64-bit) from OSGeo4W.
Tested on Arch Linux and can't reproduce there, but those are daily builds from the 2_12 branch.

So on Windows, we're able to reproduce the issue by adding a couple layers (from PostgreSQL 9.4.5 and PostGIS 2.2.0) in EPSG:3005 (BC Albers), then enabling OTF to something like EPSG:26910.
Then once we start panning and zooming the vertical lines appear like in the screenshot originally attached.

I'll test QGIS Master on Windows from the OSGeo4W installer and report back =)
Turning off multi-core rendering will reduce the artifacts and frequency, but not entirely.

Seeing the same rendering issues in Master (2.13.0, 3e61891) and Current Release (2.12.0, cd9d645) on Windows from OSGeo4W.

I can add a few layers in EPSG:3005, then turn OTF on to anything like EPSG:26910 and vertical lines appear.

Some of the most culprit layers can be obtained from public FTPs in BC.

Large files though (they're province wide), and I've uploaded them to PostGIS databases using gdal forcing 2D with '-dim 2' because no layers contain z-values but some layers will be used for topology (routing) later, but currently no M values.

Invalid geometries have been repaired too.

Road Network
ftp://ftp.geobc.gov.bc.ca/sections/outgoing/bmgs/DRA_Public/dgtl_road_atlas.gdb.zip (256 MB)

Fresh Water Atlas
ftp://ftp.geobc.gov.bc.ca/sections/outgoing/bmgs/FWA_Public/FWA_BC.gdb.zip (3.5 GB)

The Fresh Water Atlas has a good mix of layers that have different types of geometries like lakes/rivers (polygon), stream network (line), wetland (polygon), etc. Load at least those 3 layers (and the road network mpar layer) to see the vertical lines. These layers seem to be doing it the most (maybe it's because they have the most nodes?).

I'm able to reproduce it easily now =)

I add the Digital Road Atlas (layer that ends in mpar) which is in EPSG:3005.

Then I add some layers from ftp://ftp2.cits.rncan.gc.ca/pub/geott/frameworkdata/hydrology/cartographic/canada/canaddrcarto_1m_v6-0.shp.zip (94.4 MB) which are some water course and body layers but in EPSG:4269 so that turns OTF on (projecting to EPSG:3005).

Then I can see the vertical lines from the water course and body layers.

This means you might not have to download the FWA dataset to test it out.

I also noticed that the problem almost completely disappears when "Render layers in parallel using many CPU cores" is turned off.
There is still the rare vector off shoot problem from both lines and polygons but now it seems to only show one or two artefacts, and then a pan or refresh gets rid of it for a good while.

I noticed it's also re-drawing the geometries.

So a line that was like ......... now looks like ..../\\....

So it's like it's moving nodes/vertices around for some reason.