GI caching for fast camera moves

[Hannes]

I have a scene where the camera is inside the hangar of a spaceship floating above the earth (my 2nd VR challenge entry animated). The (spherical) camera and the hangar move very fast in sync.

I created a GI cache file every 5th frame and used "interpolate for animation" as blend mode (5 files to blend). I get every 5th frame rendered correctly, but all the frames in between seem to have no GI.
So how is the GI calculated? Inside the camera or in real world space? I guess it's the latter, because of the missing GI?! Or did I miss something?

[Dune]

There's just no GI in space, it's all black 

[Hannes]

There's just no GI in space, it's all black 

That's the reason!!!! 
Maybe I should call GI Joe?! (...a bad one, I know...)

[bobbystahr]

There's just no GI in space, it's all black 

hee hee hee

[Matt]

GI cache stores its points in world space, so moving objects move in relation to the points in the GI cache, causing incorrect GI.

Matt

[Hannes]

GI cache stores its points in world space, so moving objects move in relation to the points in the GI cache, causing incorrect GI.

Matt

Ah thanks for the explanation, Matt! In the meantime I created a GI cache file for every single frame and used 10 files to blend. Seems to be working.

[Matt]

If your first test showed that every frame was black except for the exact frame on which a cache file was rendered, then it means your scene is moving so fast that blending is not going to help at all because there is no overlap between each dataset. Using the blend option will only make your renders take longer. Worse still, you might get incorrect GI if any of the data does happen to overlap between frames.

Matt

[Kadri]

If your first test showed that every frame was black except for the exact frame on which a cache file was rendered, then it means your scene is moving so fast that blending is not going to help at all because there is no overlap between each dataset. Using the blend option will only make your renders take longer. Worse still, you might get incorrect GI if any of the data does happen to overlap between frames.

Matt

Matt can you elaborate a little more. What is the best way to do in such a position?

[Hannes]

If your first test showed that every frame was black except for the exact frame on which a cache file was rendered, then it means your scene is moving so fast that blending is not going to help at all because there is no overlap between each dataset. Using the blend option will only make your renders take longer. Worse still, you might get incorrect GI if any of the data does happen to overlap between frames.

Matt

Hmm, doesn't sound good...
Actually the hangar and the camera are travelling 500000 units during 300 frames. Quite a lot. I'll see how the result is. Anyway thanks again for this detailed explanation.

[Matt]

If your first test showed that every frame was black except for the exact frame on which a cache file was rendered, then it means your scene is moving so fast that blending is not going to help at all because there is no overlap between each dataset. Using the blend option will only make your renders take longer. Worse still, you might get incorrect GI if any of the data does happen to overlap between frames.

Matt

Matt can you elaborate a little more. What is the best way to do in such a position?

If your scene changes so much that the GI cache needs to be different for each frame, then the only thing you can do is calculate the GI for each frame, and choose high enough settings that it doesn't flicker. In this case, the GI cache files are useless because you can't reuse the information.

Matt

[Kadri]

Thanks Matt.

[Hannes]

If your scene changes so much that the GI cache needs to be different for each frame, then the only thing you can do is calculate the GI for each frame, and choose high enough settings that it doesn't flicker. In this case, the GI cache files are useless because you can't reuse the information.

Matt

OK, it didn't really work. As you said, Matt. 
I realized that in terms of (sun-) lighting the hangar more or less stays the same. So I'll try to delete the camera's and the hangar's animation and render it separately. If I'll comp it onto the (moving) earth's backplate it should look the same, but without the flicker. Hopefully.

[bobbystahr]

If your scene changes so much that the GI cache needs to be different for each frame, then the only thing you can do is calculate the GI for each frame, and choose high enough settings that it doesn't flicker. In this case, the GI cache files are useless because you can't reuse the information.

Matt

OK, it didn't really work. As you said, Matt. 
I realized that in terms of (sun-) lighting the hangar more or less stays the same. So I'll try to delete the camera's and the hangar's animation and render it separately. If I'll comp it onto the (moving) earth's backplate it should look the same, but without the flicker. Hopefully.

Sigh, it's always the flicker....

[paq]

Hi Matt,

With the new progressive rendering in T4, is it possible that the GI is computed using an MC brute force method ? (so no more GI sampling prepass at all) 

[bobbystahr]

Hi Matt,

With the new progressive rendering in T4, is it possible that the GI is computed using an MC brute force method ? (so no more GI sampling prepass at all) 

heh heh, that'd be telling....