I tried to reproduce your issue about OBJ export, but didn't notice problems on the DAE file I tried (but I didn't try 10 times).

I deleted my model that I used. Most of the time I uses either in .3ds or .obj. and directly imported form 3ds-max or maya. If these two formats are failed to render properly then I convert it again using any 3rd party application like Meshlab or AccuTrans.

Even if it's not forbidden, you're not supposed to do that. Who would you do that?

[:D] No One Can Stop My Curiosity [:x]

Files are different but it's not astonishing, their coordinates are not in the same space:

Thanks for the sharing it,else I think it was a bug that when I import a model which has different parts with pivot points are located in different possion is shown as a squeezed ball.

I don't see any issue about the d transparency value in MTL files.

Sorry I am trying to mention either transparency color is may not be defined or the Ni value limitation is not explained in OBJLoder.java. Because sunflow can render less than '1' value. The proof is in same post, one of the previous comment which with eta values are showing image is rendered in sunflow 0.7.2.
In v4.4 you are limited eta=1.33 that means I can't render diamond(eta 2.415),flush blood(eta0.8)?. [:))]

If you want your sky image, choose the same point of view in Virtual visit mode.

Then can you make a switch button from areal view to virtual view or viseversa without changing its point of view including field of vision angle?.
In help about photo creation ,

At a given quality level, you can still improve the image quality by choosing a bigger size for your image, then reducing the size of the computed image in an editor like The Gimp.

In these lines you are talking about to change DPI/PPI of the image?

I don't understand the goal of these keys.

I know these are the global keys and calling inside an application is default.But I am sorry, I forgot to mention its only for reference (or similar to do so). Also can you add one more key, for Photo Rendering window(F9)?.