Rebuild FG Map = Off and FG Map Size Issue

[mfire]

Hi,

I have a very long shot to render, 1000s of frames, with no cuts.  The camera does not move and a creature enters the frame from the left and  walks very slowly and exits the right frame.  I got rid of FG flicker by rendering a single frame of the scene with the creature invisible and creating an FG map with "Rebuild FG Map" = ON and then rendering out the animation with "Rebuild FG Map" = OFF and referencing the FG map I previously made.

Everything is fine on some test renders of sections of the animation, but I notice that my FG map is getting very BIG! (100s of MB).  I know that with Rebuild FG map = OFF new FG rays are appended to the FG map so it makes sense that the file is getting bigger.  My concern is that the FG map will eventually get bigger than 2 GB.  My PC has a 32 bit OS and I know that 2 GB files on 32 bit machines can cause a problem.  Will Maya eventually clip off the FG map size and not let it get any bigger or will my render just crash?  If Maya does clip off the FG file size, will I start to get my flicker back?

Thanks,

Matt

[joojaa]

My PC has a 32 bit OS and I know that 2 GB files on 32 bit machines can cause a problem.

err... no file size has nothing to do with the bitness of the os but rather the allocation table size of your disk and what filesystem it is formatted with.

2 gb limit is for sued memory not files on disk. There however is a maximum disk file size too but its not the same limit, it depends on WHAT operating sytem your on and WAHT options you used when you formatte dthe dsik. Ive use dplenty of 32 bit programs with bigger than 2GB files as a fact. That doenst mane there might not be a 2g filesize limit but thest basically just how you formatted your hardrive has nthing to do with os bit depth.

Besides youll kill your machine at some point regardless if it grows at 100megs per frame that is then 100 gig file and most oses dont allowfor that big files even IF you were 64 bit.

In any case set up a biger filetar area it will make your file smaller,

Will Maya eventually clip off the FG map size and not let it get any bigger or will my render just crash?

Try and see if it does then deal with the issue. then spit the render up by say 100 frames... maybe with few frames overlp and blend in posr´t hat will take care of the flicker if any. 

PS: mr CAN use many fg files.

[mfire]

Joojaa,

Thanks for the info and tips.  I'm running WinXP SP3 and my HD is formatted NTFS.

I thought about the idea of breaking up the render into smaller sections and blending them in over several frames after I posted.  If the fg map causes the render to die I can always do this.  BTW, the fg map I'm currently testing with sections of animation has grown to 186 MB with FG rays = 1000 for about 300 frames (1280 x 720).

A couple of related questions on how the fg map actually works.

I notice that the fg map grows slightly with each frame, but not nearly what the original fg map was for the first frame.  What is mr actually doing when it appends to the fg map when fg rebuild is off?  If the initial fg map is for 1000 fg rays then it is not casting another 1000 fg rays for the second frame and adding it to the initial 1000 fg ray fg map.  I believe more fg rays would cause the render to be brighter (as I've seen when I compare the same scene rendered with fg rays = 100 to fg rays = 500).

This also brings up an issue for rendering the initial fg map:  does it matter what is in the scene for this initial fg map render?  I've taken the precaution of making all objects invisible except for the lights and walls of the environment for the initial render. I assumed that trace depth (=2 in my case) might give different results if there is a lot of geometry in the scene. However, since the fg rays are cast from the camera (which is stationary for my scene), and the fg map is "modified" or added to for each frame this might be an unnecessary precaution. So, if the camera is not moving, would it really matter what is in the scene for the first frame?

Thanks again for the help you've given me and many others over the years.

Matt

[joojaa]

HD is formatted NTFS.

still the max filesize is determined by your block size and what os you had when you formatted the drive (as opposed to what you have now)

What is mr actually doing when it appends to the fg map when fg rebuild is off?

final gather makes for points to sample, sometimes the measuring metric notices areas where the original pattern was not sufficent to give the resolution needed. It then proceeds by adding more points to that area. This does not happen for thw whole picture so it only grows slightly over time. This is good because a bigger map renders slower.

does it matter what is in the scene for this initial fg map render?

Yes.

However, since the fg rays are cast from the camera

Well not actually the pattern is determined form the camera view the rays are cast form the scene. Improtions work like you describe tough.

So, if the camera is not moving, would it really matter what is in the scene for the first frame?

Yes, and no depends a bit. The system would fix hats there in later stage but it might be faster to actually have data beforehand. So it might be best to render the sequsce out of order might produce the best results because you would account for the futture as well as past.

Alternatively you can render just the fg map beforehand.

[rtist]

In this case, just render the background once, and composite the character and shadows separately. 

FGmaps are based on a stationary scene, you can't bake a map to work with a character in motion.

[joojaa]

Hes not baking a fg map to atexture, its abit unfortunate form of naming convention.

FG map is the seed for the sample matrix as well as a texture map that has baked the solution into it. Now both are baked if you do it over in separate passes. But i can assure you:

you can't bake a map to work with a character in motion.

You can! Especially since hes only baking the positions of the sample points. Its a different KIND of map.