Gaia Sky 3.6.6

Features

move volumes earlier in the rendering pipeline, because they now write to the depth buffer.
check for dataset incompatibilities and ask user to confirm action when selecting incompatible datasets.
add window size and resolution of external view in settings, when the external view is active.

attitude indicator not scaling with units-per-pixel value in spacecraft UI.
incorrect initialization of label threshold in volumes in VR mode.
entering panorama mode resets back-buffer scale. The issue was that the dynamic resolution reset routine was always applied, and not only when the dynamic resolution setting was on.

replace arbitrary precision add() call with double-precision one to compute spherical coordinates of objects. Double-precision is more than sufficient for that purpose.