Bug report #1993

North arrow changes direction (with OTFR disabled and projected CRS) at very high/low zoom levels

Added by vince - about 15 years ago. Updated over 12 years ago.

Status:Closed
Priority:Low
Assignee:Magnus Homann
Category:Projection Support
Affected QGIS version:master Regression?:No
Operating System:All Easy fix?:No
Pull Request or Patch supplied:Yes Resolution:
Crashes QGIS or corrupts data:No Copied to github as #:12053

Description

Depending on the zoom level, the north arrow points sometimes north, sometimes south...

dpts.zip - Example of shapefile (173 KB) vince -, 2009-10-10 11:38 AM

qgis_screen.png (63.6 KB) Giovanni Manghi, 2009-10-10 03:32 PM

Associated revisions

Revision a02d448b
Added by Alessandro Pasotti about 6 years ago

[spatialite] Fix pk-less queries cannot be retrieved by id

Fixes #1993 - Zoom to feature" does not work

This actually fixes many more bugs related with the
QGIS generated feature id (incremental) when using
queries that was not consistent when using
QgsFeature request with ids or bbox.

This is not a regression: the same error is in 2.18

History

#1 Updated by Giovanni Manghi about 15 years ago

can you post sample data? are you using a geographic or projected crs? otfr on?

please try to be more specific when posting bugs otherwise it becomes hard to check them and confirm the bug.

#2 Updated by vince - about 15 years ago

Ok, sorry. You will find appended a shapefile with French limits. Set project to Lambert 93 (EPSG 2154 or 2174, I don't remember) and try various zoom levels. The arrow move back and forth from north to south.

#3 Updated by Giovanni Manghi about 15 years ago

I'm not really very deep into projections matters, so I may not be able to explain this correctly, and if I'm saying something wrong please correct me.

Try add a layer defined in wgs84, for example a shape of the world borders: to let your France shape overlap the world borders you will need to enable OTFR. If you define wgs84 as project CRS, then you'll see obviously all aligned and the north points upwards, regardless the zoom level.

Now change the project CRS to a projected system and zoom to your France layer, you'll obviously still see the north upwards, but then when you zoom out the north arrow will start change the direction because the world border layer "wraps". It seems to me that the direction changes depending on what you have in the centre of the canvas. ***

I'm not sure why this also happens when you zoom in a lot, but I see that it happens when the scale reads "4 cm", so I guess that is not really important.

I'm also not really sure why this happens with OTFR not enabled and the project defined with a projected CRS. Interestingly it seems to happen always when zooming in (a lot) regardless the projected crs, but I found that when zooming out with certain projected crs, the north arrow does not change direction. As I said I'm very scarce about this matters, so maybe there is a reason that makes perfect sense for this behaviour.

***
Doing such test I found a bug that crashes qgis under ubuntu, but I will open a separate ticket.

#4 Updated by vince - about 15 years ago

To me, it is wrong at large and small scales. Look at the screenshots I made, always in Lambert 93 system.

#5 Updated by Giovanni Manghi about 15 years ago

Replying to [comment:5 vince]:

To me, it is wrong at large and small scales. Look at the screenshots I made, always in Lambert 93 system.

yes (if you are using otfr disabled), it is what I wrote in my last sentence. But again, it doesn't happens with all the projected crs, so maybe there is an explanation, maybe is a just a bug.

#6 Updated by Paolo Cavallini over 14 years ago

Not quite sure it's really a bug. Further investigation needed

#7 Updated by Giovanni Manghi almost 13 years ago

  • Target version changed from Version 1.7.0 to Version 1.7.4

#8 Updated by Paolo Cavallini over 12 years ago

  • Target version changed from Version 1.7.4 to Version 1.8.0
  • Affected QGIS version set to master
  • Crashes QGIS or corrupts data set to No

#9 Updated by Magnus Homann over 12 years ago

  • Pull Request or Patch supplied set to No

There were two things
1) Zoomed in: A tolerance for very small delta-x and delta-y prevented proper calculation of rotation.
2) Zoomed out: The center of the canvas was used for grabbing delta-x and delta-y. When zoomed out, the center of the camvas could possibly be "on the other side of the globe" compared to the layers in question.

A fix is in https://github.com/qgis/Quantum-GIS/pull/205

#10 Updated by Magnus Homann over 12 years ago

  • Pull Request or Patch supplied changed from No to Yes

#11 Updated by Tim Sutton over 12 years ago

  • Status changed from Open to Closed

Applied patch with 90e7baa

Closing ticket (thanks Magnus!). Please re-open if problem persists.

Tim

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