Grids wrong close to "equators" for small FOV

[Nick Fedoseev]

version 0.13.1.90
See attached images

1. Horizontal grid:
- 10" label is in place of 20"
- 10" line is absent
- 40" line has a stable artefact
- 40" label is distorted

2. Vertical grid:
- 5" label is in place of 10"
- 10" label is in place of 20"
- 30" label is distorted
- 5" and 15" lines are absent

[Nick Fedoseev (nick-ut2uz)]

Similar behavior is for Az and Eq grids as well.

[Alexander Wolf (alexwolf)]

Please try disable atmosphere and check again.

[Nick Fedoseev (nick-ut2uz)]

Atmosphere switch has no effect for this bug.

[Alexander Wolf (alexwolf)]

I can't reproduce issue on my linux. Possible rendering issue, related to some graphics cards/drivers?

aw@fomalhaut:~$ lspci | grep VGA
01:00.0 VGA compatible controller: NVIDIA Corporation GF116 [GeForce GTX 550 Ti] (rev a1)

[Nick Fedoseev (nick-ut2uz)]

Sorry, I am not a OpenGL guru.

Just verified. The same bug can easily be reproduced on my second PC (DELL notebook with GeForce video) for 0.12.4 release. The artefact is slightly different.

This PC equipped with AMD Radeon 6800.

If near horizon, switching on/off Atmosphere just moves stars and grid accordingly to the correction , the bug itself is always seen near zero line.

To see the bug for Eq grid:
- center view anywhere at dec = 0, for example at HIP 26149.
- zoom to FOV ~0.02

[gzotti (georg-zotti)]

I can confirm it. (WinXP, NVidia 8200). FoV < 0.03° is when the grid shows tens of arcseconds.

[Nick Fedoseev (nick-ut2uz)]

See StelPainter.cpp, function void StelPainter::drawSmallCircleArc

I do not know exactly what is the purpose of

if (rotCenter.lengthSquared()<0.00000001)
 {
  // Great circle
  // Perform the tesselation of the arc in small segments in a way so that the lines look smooth
  fIter(prj, start, stop, win1, win2, tessArc, tessArc.insert(tessArc.end(), win2), 1, rotCenter);
 }

But coordinates are distorted here.

I just tried to comment out that portion of code, leaving the opposite branch, the bug has gone.
The proposed patch is attached.

[Alexander Wolf (alexwolf)]

Nick, your patch introduce other bug, but it's good point to view code, thanks you! I'm changed condition and now all grids seems good for me. Can you check it on Windows (r7337)?

[Nick Fedoseev (nick-ut2uz)]

Seems the bug has gone.

Thanks!

[Alexander Wolf (alexwolf)]

Thanks for testing!

A fix has been committed as revision 7337 of the trunk branch of Stellarium's Bazaar repository at Launchpad: http://bazaar.launchpad.net/~stellarium/stellarium/trunk/revision/7337