Trouble with shadows using radiosity & HDRI

[billtheia]

I think that I must be missing something. I'm experimenting with HDRI backgrounds. When I use final quality renderworks, shadows render as I would expect but when I use final quality RADIOSITY, I get no shadows at all.

Help!

See attached pic.

[michaelk]

Bill

Final Quality Radiosity adds ambient light.

Try a Custom Radiosity with the ambient light turned off.

Michael

[Dave Donley]

Hello Bill:

For radiosity the triangle sizes are probably too coarse to capture the shadows cast by the relatively smaller podium object. You can change the Init Detail size in the Custom Radiosity Options dialog to set the triangle sizes small enough to get the shadows there. The Show Color Coded Preview option in the Custom Radiosity Options dialog will let you see the triangle sizes as yellow triangles.

For most cases it is easier to use Custom RenderWorks with Final Gather on. For this scene set the Detail Size to something like 1" to get the edge of the podium. For a building- or room-sized model the 2009 defaults of 1' detail size and 10% accuracy would work OK but this is smaller than that.

[michaelk]

Dave

Am I wrong about ambient light in Final Quality Radiosity?

Michael

[billtheia]

Hello Bill:

For radiosity the triangle sizes are probably too coarse to capture the shadows cast by the relatively smaller podium object. You can change the Init Detail size in the Custom Radiosity Options dialog to set the triangle sizes small enough to get the shadows there. The Show Color Coded Preview option in the Custom Radiosity Options dialog will let you see the triangle sizes as yellow triangles.

For most cases it is easier to use Custom RenderWorks with Final Gather on. For this scene set the Detail Size to something like 1" to get the edge of the podium. For a building- or room-sized model the 2009 defaults of 1' detail size and 10% accuracy would work OK but this is smaller than that.

Thanks, Dave. Can you give me more detail about how Color Coded Preview works? I can see red and yellow areas in the scene but it's not clear to me what they mean.

Also, is Michael right? Does radiosity add ambient lighting?

[Dave Donley]

Hello Michael and Bill:

Final Quality Radiosity mode uses the layer's or viewport's ambient light setting. A lot of times the ambient may be too strong and in combination with the auto exposure adjustment the ambient can cause the scene to look very flat.

I recommend turning off the layer's or viewport's ambient while adjusting the lighting and only adding a bit of it if necessary once you know what the scene will do with the indirect lighting and auto exposure going.

There is an option with Custom Radiosity for the remaining indirect light to be pumped into ambient light, that may be what Michael is thinking of?

[Dave Donley]

The help text in the dialog should mention what the colors mean - red is objects that will only receive light from their neighbors but not re-emit it, the yellow triangles are to show the initial detail size.

You want the initial detail size to be fine enough to capture the shadow edges from the direct lighting, which in this case is the shadow edges from the podium. If the initial detail size is too large the shadows will not be evident in the lighting; if it is too small then the radiosity processor will be doing excessive work.

[billtheia]

I looked at the help file but it's not clear what exactly I should be after with these controls.

Object Inclusion:

If something is red in the preview, will it NOT cast a shadow? Should I be setting Object Inclusion so that nothing red (so that is shows gray) or so that things that don't need to reflect light (like the human figure in my previous image) are red?

Initial Detail:

What exactly do the yellow triangles mean? Should I be setting Initial Detail so that I see large triangles, small triangles, or no triangles (so that everything shows as gray.)

Is there some comprehensive resource and/or tutorial that can help me with this stuff? I bought the Renderworks tutorial DVD but it only really scratched the surface and it didn't cover radiosity.

[Dave Donley]

Hi again Bill:

Did you read this FAQ on radiosity already? It may help:

http://techboard.vectorworks.net/ubbthreads/ubbthreads.php?ubb=showflat&Number=60037&Main=13944#Post60037

[billtheia]

No, I didn't see that. It looks like it's just what I need. Thanks.

[Dave Donley]

Good I hope that does help.

Note that Custom RW with Final Gather should give a nice result and is much easier to setup and manage.

There are few cases that require using the radiosity render modes anymore. One would be an interior that has localized direct lighting that needs to be bounced around a few times to reach the whole room.

Other than that case:

Good results = ambient low/off + HDRI + FG + auto exposure

HTH!

[billtheia]

Thanks again, Dave. At least half of my work is interior which is why I'm messing around with raidosity in the first place.

[billtheia]

OK. I think that I'm starting to get the hang of this but now I've run into another stumbling block.

I can now get both radiosity and renderworks to give me the shadows that I'd expect when using HDRI backgrounds BUT when I turn on final gather (in rad. and rw) my shadows completely disappear.

See attached images.

I have a scene that is lit only with an HDRI background. If I use radiosity or renderworks without final gather, I get shadows cast by the light source in the HDRI. When I turn on final gather to add some indirect light to the ceiling, all shadows disappear completely. The attached images use 36" for detail size and 50% for accuracy. I've used other settings but none bring the shadows back.

My ultimate goal is to use HDRI backgrounds to light interior scenes.

Help, again!

[billtheia]

Now I have another problem. I'm getting light leaks at the junctions between walls, ceilings, & floors when I use radiosity. There are NO gaps in the model and I don't get these leaks when using renderworks.

See attached image.

Can someone tell me why that is happening?

Thanks.

Edited October 30, 2008 by billtheia

[Dave Donley]

Hello Bill:

36" is too big for the FG detail size (that might be appropriate for a site model of several large buildings), which likely is causing the lack of shadows and the light leaks. Try a much smaller value like 1". Set the accuracy low to say 10% to start to compensate a bit for the smaller detail size, then work up from there to improve quality.

In 2009 the defaults for FG are 1' and 10%. I have found that you only need a few size values depending on the size of the objects in the scene. 1', 4", 1", 0.1" work well for me, and I use a few accuracy values like 10% 30% 70% or 80%.

Final gather can be sufficient for interiors as long as the one bounce indirect lighting is kept in mind. Note that if you use an HDRI it fills in pretty well because the light reaches a lot of surface area to start with.

Also to help remove light leaks make sure that your ceiling and floor have edges at the wall interior sides. This is true for radiosity especially but should also help with final gather light leaking as well.

These images used FG size of 2", accuracy of 80%, and auto exposure of 180% to make the walls brighter.

Edited October 30, 2008 by Dave Donley

[billtheia]

Thanks again, Dave. I really appreciate your time and patience.

I'll try changing my FG settings.

Could you post your vwx file? I'd like to see all of your settings and see if I can replicate your results on my computer.

Thanks.

[Dave Donley]

Hi Bill:

Sorry but I can't post the vwx file - I didn't model it (I think it may be an Australian one) and I don't want to get in trouble. The HDRI is one of the new library from LightWorks that I hope to post here soon but it's not ready yet. I'll post that to the RW forum.

[billtheia]

Bummer.

Can you tell me how long that took to render?

Was it done with radiosity or renderworks?

Are shadows ray traced or shadow mapped?

If you could, a run down of all settings would be really helpful.

Thanks.

[billtheia]

I think that I must be missing something. I'm experimenting with HDRI backgrounds. When I use final quality renderworks, shadows render as I would expect but when I use final quality RADIOSITY, I get no shadows at all.

Help!

See attached pic.

Hello Bill:

For radiosity the triangle sizes are probably too coarse to capture the shadows cast by the relatively smaller podium object. You can change the Init Detail size in the Custom Radiosity Options dialog to set the triangle sizes small enough to get the shadows there. The Show Color Coded Preview option in the Custom Radiosity Options dialog will let you see the triangle sizes as yellow triangles.

For most cases it is easier to use Custom RenderWorks with Final Gather on. For this scene set the Detail Size to something like 1" to get the edge of the podium. For a building- or room-sized model the 2009 defaults of 1' detail size and 10% accuracy would work OK but this is smaller than that.

Just wanted to update this post for those of you who are following.

Dave was right about the detail size setting in final quality radiosity. I changed them and got shadows to appear. See attached pic.

[billtheia]

OK. I think that I'm starting to get the hang of this but now I've run into another stumbling block.

I can now get both radiosity and renderworks to give me the shadows that I'd expect when using HDRI backgrounds BUT when I turn on final gather (in rad. and rw) my shadows completely disappear.

See attached images.

I have a scene that is lit only with an HDRI background. If I use radiosity or renderworks without final gather, I get shadows cast by the light source in the HDRI. When I turn on final gather to add some indirect light to the ceiling, all shadows disappear completely. The attached images use 36" for detail size and 50% for accuracy. I've used other settings but none bring the shadows back.

My ultimate goal is to use HDRI backgrounds to light interior scenes.

Help, again!

Hello Bill:

36" is too big for the FG detail size (that might be appropriate for a site model of several large buildings), which likely is causing the lack of shadows and the light leaks. Try a much smaller value like 1". Set the accuracy low to say 10% to start to compensate a bit for the smaller detail size, then work up from there to improve quality.

In 2009 the defaults for FG are 1' and 10%. I have found that you only need a few size values depending on the size of the objects in the scene. 1', 4", 1", 0.1" work well for me, and I use a few accuracy values like 10% 30% 70% or 80%.

Final gather can be sufficient for interiors as long as the one bounce indirect lighting is kept in mind. Note that if you use an HDRI it fills in pretty well because the light reaches a lot of surface area to start with.

Also to help remove light leaks make sure that your ceiling and floor have edges at the wall interior sides. This is true for radiosity especially but should also help with final gather light leaking as well.

These images used FG size of 2", accuracy of 80%, and auto exposure of 180% to make the walls brighter.

Another update. Again, Dave was right that the final gather size was at the root of my disappearing shadows. His recommendation of 2"/80% might result in better images but they dramatically increase render times. I found that 3"/10% was the sweet spot for my rendering. Those settings gave me the shadows I was looking for while keeping render times down to an acceptable level. Going to 1"/10% increased my rendering times five fold while only marginally improving the quality of the rendering.

See attached pic

[billtheia]

Now I have another problem. I'm getting light leaks at the junctions between walls, ceilings, & floors when I use radiosity. There are NO gaps in the model and I don't get these leaks when using renderworks.

See attached image.

Can someone tell me why that is happening?

Thanks.

...to help remove light leaks make sure that your ceiling and floor have edges at the wall interior sides. This is true for radiosity especially but should also help with final gather light leaking as well....

I still haven't gotten a handle on this light leak thing.

I've looked at the "edges" of everything and all seems to be correct. The walls are walls and the ceiling & floor are 1" thick extrudes. I've tried moving ceiling inside of walls and on top of them - no change. I've even tried moving the ceiling down so that it overlaps with the walls and still no joy.

I think that it's something in radiosity because renderworks with similar settings doesn't suffer this problem.

See attached pic & vwx file

[Dave Donley]

Hello again Bill:

The top surface of the ceiling is not covering the top edge of the wall, it is co-located with the top of the wall. If you move the top surface of the ceiling above the top edge of the wall it will obscure the top edge of the wall and the ceiling leaks will go away.

Similarly the floor edges go out to the outside edge of the walls. If the floor edges were instead terminated at the inside edge of the walls then the floor leaks go away.

If a surface is co-located with another that is supposed to obscure it then light can leak at that edge. The obscuring surface has to be offset from the other one for the light to not leak.

HTH

[billtheia]

Thanks, once again, Dave. I misunderstood your earlier directions.

Moving the ceiling to cover the tops of walls and moving the floor to reside inside the walls, fixed the light leaks.

Here are updated pics and vwx file for posterity.

[billtheia]

I realize now that I posted this question in the General Questions forum when, in fact, it should have probably been posted in the Renderworks Forum.

If the folks at NNA are so inclined, I'd be fine with them moving it there.