Print at Jun 20, 2018 1:09:33 AM

Posted by okh at Oct 26, 2016 10:17:34 AM
Re: This is cheating...
@Cec

Yes to pretty much all you say. Thanks for your patience in your testing. Most useful.

First, you will find no objection to your point that the 3D landscapes have great advantages and is inevitable for the high quality rendering. And yes, hiding the levels (Shift-Ctrl-H for non-Mac users) is a must. Having a separate 'terrain' level to hide/unhide is almost always a good idea. Or indeed, keep the terrain in a separate file and copy in for rendering.

So my sky-texture advocacy is really about something else: How to break up the default prairie horizon that looks so misplaced in this part of the world. But, with ever so many shortcomings as you point out.

..the distortion that we have to adjust for:
When stretching it to a dome, the clouds will appear more correct from one point of view - but not if you turn around. But then, clouds and horizons really are two different things. In real life clouds are not glued to the heavenly dome, but pass in relatively straight lines (forget the meteorology for a sec). This means that fluffy clouds high in the sky will look distorted on a background picture. Except maybe when they hover just above the horizon/mountains/treeline.
Using a non-square image will not give the best result, as the sky is actually projected from a square image.
Hmm, this is interesting. My first attempts used panoramas from a camera which indeed were long and narrow. That will look wrong. The sky certainly does need to be stretched up to the zenith. Still, I wonder about the proportions of a good sky texture. In my world, the sky comes in the ratio 4:1 - that is a 360° horizon and 90° up to zenith. Which is so far the ratio I have assumed would be the best. But then, there is the equirectangular projection which will 'compress' the lower part of the image and stretch the upper part of the image. Which probably means a square image could be easier to work with.

I tried with a 3600:900 grid, result below. I am not yet convinced that a square is better, but maybe I am missing something. Views?

What is a slight annoyance, though, is that the 3D window and the photo rendering appears to project differently. Especially for the higher mountains the effect is noticable.

Now, this becomes pretty much a theoretical discussion. For the (inferior)sky-texture technique one needs to work only along a narrow strip at the bottom of the picture. For the upper part, the sky dome, it is better to use a gradient (or a contrast colour to be masked of later). In fact, I suppose the only planetary objects would render correctly above on sky-texture projection - so for a night sky, maybe.

And also - do not get me wrong - this is sidetracking Cec' original issue. So ignore this and scroll far back if you are looking for how to make nice sceneries... :-)

ok