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Burned by a "gotcha!"*

I lost about 4 hours of work yesterday thanks to an odd set of circumstances, documented here in hopes of helping others to avoid or troubleshoot similar problems.

Lately, I've been trying to clean up and simplify a lot of my lighting designs, attempting to use light sources contained in fixtures and lamps within the model provide much of the illumination. Towards that end, yesterday I was working with several models of recessed and surface-mounted ceiling fixtures, each with an integrated light source I'd added by editing the furniture library (as described in OK Hoff's excellent guide.

As part of my experimentation, I wanted to compare several different fixture designs with light sources of varying strengths, sizes, and colors. For future reference, I kept a detailed log documenting each configuration I tried, along with a small, high-quality render of the resulting scene.

Since one of the most common lighting problems I have is burn-out (overexposure) of adjacent wall and ceiling surfaces, I positioned the 'eyes'/'lens' of my Virtual Visitor closer to the floor than usual, with the viewport angled upward. This placed within the field of vision the fixture, the section of ceiling surrounding it, the adjacent wall, and furniture in the general vicinity. To simplify matters, I hid all light sources within the plan other than the fixture or fixtures under test. (At times I added 'floating' light sources to simulate ambient lighting.)

All-in-all, I tested thirty or forty different configurations, with a couple dozen logged for later reference. Eventually I had what I felt to be an acceptable blend of directed and ambient light sources -- or at least that's how it appeared based on a low-resolution rendering:

As it was nearly time for supper -- or definitely past time for lunch -- I decided I'd let the PC crank out a high-resolution version while I grabbed something to eat. After framing the shot from a slightly higher viewpoint, I decided to run one last low-res render at Quality Level 3 as a final check on intensity

---and was met with what I first thought to be an all-white image:

This made no sense: All I had done was stand up (so to speak), changing the Virtual Visitor's eye height from three-and-a-half feet to five-and-a-half; I hadn't touched a light source or changed time of day.

I dropped the viewport back to 3'6": everything rendered perfectly. I went back to 5'6", and again the image was blown out. The same thing happened at 4'6", as well. Somehow, at 3'6" there was a sweet spot -- but nowhere else.

It turns out my Virtual Visitor was inside a speaker. A Bang & Olufsen BeoLab 8000, as I recall, which I presume must be around four feet tall. Somehow, I'd managed to drop the Visitor in exactly the right spot for most of the cast rays to be attenuated, but without any accompanying blocking or distortion of the scene. I hadn't noticed this overlap, as I had positioned the Visitor blindly: When the living room ceiling is visible, it obscures everything below. (Even with the ceiling hidden, it took me a while to find the problem; with a cross-section of only a few inches in diameter, the B&O's 2D representation was hidden by that of the Visitor's.)

In retrospect, I probably should have found it odd I was able to define so many high-powered light sources without it looking like---

well, looking like .

Admittedly, this isn't likely to be a problem often encountered; in fact, I don't know if I could duplicate it if I tried. Still, if I only manage to prevent one person from falling down this particular rabbit hole, I'll still have saved someone enough time to listen to any one of Wagner's operas, roast a 20-pound turkey, or watch the director's cut of Heaven's Gate. smile


* Gotcha. [American?] English colloquial contraction of "got you," as in "Got you by surprise!" A prank, trick, or hard-to-foresee problem or difficulty.
[Jan 24, 2016 4:38:17 PM] Show Printable Version of Post    View Member Profile    Send Private Message [Link] Report threatening or abusive post: please login first  Go to top 
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Re: Burned by a "gotcha!"*

Strange story! smile
I guess the speaker was covered with some kind of half transparent material through which the virtual visitor was viewing. You could have seen that in the 3D view except if that surface is very close to the point of view, because OpenGL requires the program to set an interval in the axis of view where objects will be taken into account and displayed (see viewing frustrum ), probably for performance reasons. SunFlow doesn't have this limitation and this may result in a different result for very close objects.
Emmanuel Puybaret, Sweet Home 3D developer
[Jan 25, 2016 7:17:49 AM] Show Printable Version of Post    View Member Profile    Send Private Message    Hidden to Guest    http://www.eteks.com [Link] Report threatening or abusive post: please login first  Go to top 
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