Lightmapping clarification - Unwrap UVWs

[path-to-star]

I need to clarify something from a lesson I was reading, but a few things are not working in the ED the same way for me as the lesson explains. I export out of 3dsMax to get that out of the way.
In hourences lightmapping lesson, he explains two ways to set proper light mapping UVs. First using a second unwrap modifier as channel (2) before you export your model. The second option would be to let the UDK handle it. The first option being recommended for better accuracy.

Ok, here is where things don't make sense. In this picture he shows his modifier stack having one Unwrap UVW set above a model that is still in a polygon state which would only have default mapping.
My question is: Say you already had a UnwrapUVW mapping your model, is he saying to add a another ..a second Unwrap with it's channel set to (2)?
Because the way he's showing it, he has only one Unwrap set to (2), but then how would the box under that modifier have any coordinates other than the default if you didn't have a second Unwrap/ or UVW modifier set to (1)? Being that it's just a simple box I'm assuming the box in the lesson is using the generic mapping coordinates for the first channel. I guess this would work, but with a more complex model I would think you would need two unwrap modifiers in your stack? That is my main question.

And, does all this lightmapping theory apply to standard UVW modifiers, or only Unwraps? What I mean is, would it be sufficient to set your channels in standard UVW if you didn't need to use an Unwrap Modifier?

Last: where is bforceDirectLightmap hourences mentions? was this replaced with a new name?

[obihb]

I don't know the tutorial but based on this post with this shot, I'd say he is using the default Box UV's in channel 1 and simply adding channel 2.

With that said, if you had to modify UV's on channel 1, of course you'd add a modifier for that. Also, if you collapsed the stack you would not have the modifier visible anymore so to go purely on what the stack suggests is not accurate. Simply add a modifier, check what the UV's look like and modify if you want. Collapsing the stack will not kill your UV's and at any point you can add another modifier to modify any channel of UV's you wish or add any additional channels.

I don't really understand your 2nd question. What do you classify as a standard UVW modifier if you don't mean the UVW Unwrap?.

All I can say is this. If your model is one of Max's default primitives, it would have a channel 1 UV set by default and that is all. For any custom model you need to create a channel 1 UV set to map your model with. For any other channels you want or need, you need to create them in all cases for any model. The only reason why most models need channel 2 UV's for light mapping is because you need a unique set. This means no overlaps on the UV set. So, if in a case you had a completely unique set on channel 1, you don't even need a channel 2. But in any other case you do need it.

Not sure if this helps you at all but I think my explanation is clear and it's pretty much as simple as that.

As for the bforceDirectLightmap, I'm not sure. You can always search this in the docs. It may very well be something that changed along the way of the UDK's development.

[path-to-star]

Hello obihb!

if you collapsed the stack you would not have the modifier visible anymore so to go purely on what the stack suggests is not accurate.

True, but his stack was not collapsed in the picture, it was a box. I understand that 3dsmax generates default mapping coordinates on Ch1 for polygonal models that have not been converted/collapsed.
What I'm asking is, how do you go about adding the second lightmass channel in 3dsMax? What is the procedure? Are you just dropping in another Unwrap UVW on top of the first one and simply setting that second Unwrap to channel 2? Or do you have to go into that second Unwrap and do something else? Obviously the first Unwrap UVW is being used to control the texture on your model, but I don't get how the UVW for light mass would be setup in 3dsMax. That tutorial did not help me.

I don't really understand your 2nd question. What do you classify as a standard UVW modifier if you don't mean the UVW Unwrap?.

There is an Unwrap modifier and a more simple UVW modifier in 3dsMax. I was just wondering if the light mass engine would respect the channels of a simple UVW as it will an unwrap?
Based on the tutorial they didn't mention a simple UVW, they say to use an unwrap, and I don't always like to use the more complex Unwarp for simple models. but I wasn't sure how the Lightmass engine would handle the simple UVW modifier as it is not mentioned in the lessons I've seen.

I don't know the tutorial but based on this post with this shot, I'd say he is using the default Box UV's in channel 1 and simply adding channel 2.

Yes. Thats good, I didn't know if the lightmass engine of the UDK accepted the data from a standard UVW, but that makes things easier. good!
Here was the full tutorial by the way. Hourences has great lessons, I just had a few issues on this as I think his version of UDK is older. http://www.hourences.com/tutorials-ue3-lightmapping/

The only reason why most models need channel 2 UV's for light mapping is because you need a unique set.

You mean..one for the main texture and the second channel for the lighting? Thats how I understand it.

This means no overlaps on the UV set.

No overlapping on the second UV channel which is the channel the lightmass uses.. right?

[obihb]

Ok, yeah, sorry, the UVW Mapping modifier does some auto mapping procedures but yes it will also affect the UV's for Lightmass just as the Unwrapper would. Both modifiers are tools to create UV's and both modifiers will affect channels in the same way. Which channel you pick, is the one being modified.

Yes, the 2nd channel is the default used by Lightmass and yeah, that should have no overlapping. My point before was just to say that channel 2 is not the only channel that will work for Lightmass. You can set any channel, even channel 1 if the UV's supports it.

[path-to-star]

I see, thanks for this clarification. well explained obihd!

Yes, the 2nd channel is the default used by Lightmass and yeah, that should have no overlapping.

Thanks again obihb
Now that I think about my first question, and what you said here. I think I got it.

I guess all you're really doing with the second channel is unwrapping the model. I don't think the second channel even needs a texture. Therefore, you're just using the second Unwrap to separate the UVs, ..then flatten the model and export it.

[obihb]

Yes, exactly. You're not texturing on channel 2 or adding textures in that case, in fact the "texture" will be the light map. You're not creating a texture, just a UV set.

[path-to-star]

Yes, exactly. You're not texturing on channel 2 or adding textures in that case, in fact the "texture" will be the light map. You're not creating a texture, just a UV set.

Beautiful, thank you for confirming this!
See, I knew I took off work on Sunday for a good reason.

EDIT: well I tried one of your suggestions and it worked pretty well!
Check it out!
http://www.pyramid-of-wisdom.com/ch_fixed.jpg

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