Questions about Light Maps

Hi guys, this is my first attempt to do light maps, I’ve read epic docs about it and made a couple researches and learn some rules and techniques to do such thing, but I still have some questions.

1 - My model has multiple UV sets for textures, can I also do multiple UV sets for light maps ??

2 - Can I have massive distortions on that UVs without any poor results ??

3 - I’ve read that low resolution light maps is more for modulate assets that will be repeatedly placed on level, so can I do light map resolution 512x512 or 1024 or even 2048 for assets that is going to be place just once ??

4 - Again about distortions, following the rules I should leave this part of my object all together, but doing so will result on a massive result, is that correct ?? If no, what would be a alternative for that exemple ??

An automatic light map generated by Unreal I get some issues, I think I can handle with the rest of object, but this very part I am not sure and have no idea what to do

You get best lightmap results if you do UV’s by hand, and you keep the amount of seams and the UV islands as few as possible. When you do that, you can usually lower the resolution of the lightmap and still get good results because it makes better use of the UV space.

You want to avoid stretching otherwise the pixels can get distorted, it’s not entirely avoidable but you want to minimize it as much as possible.

You can only use one UV channel for lightmaps.

Thank you for your reply, i’m a little confused about what you said of few UV island as possible, because if for normal maps accuracy must be split at every hard edge and for light map for every corner naturally you will have more UV Island on your Light Map UV, in this very case combining 5 UV sets into one I will have a lot Islands, I will do that work and see what happens, but that part of picture one I dont know how to split, I will try to cut the top when it becomes a rounded shape!!!

Hey that is not that bad from the engine for your lightmap here…you can also increase your light map resolution to minimize the seam…important note: will the player be able to watch the top of your vehicule? If not, the seam isn’t very noticeable i guess…
? If yes, check your UV by hand like mentioned before :wink:

Smoothing groups get separated on import into UE4, that doesn’t matter when you’re setting up your UV’s in your 3D program. Each UV island means you need space between them, and the empty space is a waste.

And it’s better to have good UV’s and a low resolution lightmap than to just increase the lightmap resolution

I am still struggling with this, I just set up a new UV and I now understand and agree about what darthviper said, letting continuous mesh together actually has a better result and more friendly layout. I do have some bleed on couple spots don’t know why, I set up room space for 2 texels on my UV grid on Maya and also 2 texels for the wasted area, am I missing something ?? I just don’t get it.




Your mesh is split up far too much, you see all of those thin and tiny pieces? Those are the issue, they don’t likely need to be split off from the rest of the vehicle, and because they’re so small to get a good result you would need to increase the lightmap resolution really high. To get the best result, you need to do the whole UV mapping by hand.

By the way, if this vehicle is going to be driveable or animated, then you don’t need lightmap UV’s since it will use dynamic lighting.

I see, my goal is for marketplace, its my first attempt so I want to make sure that every thing is setting up for all purposes. Do you think 21k Tris is a good amount for this kind of vehicle ?? And what about padding and grid snap, I’ve seen some tutos saying about snapping to grid, but they were all cubes, so is that necessary to snap all split edges for all kinds of shapes even distorted those for accuracy ?? For hard edges I read that they must be split for a better result, is that applied for any hard edge and/or 90 degrees angles shapes ??

For a shape with any curves, you can’t snap it to the grid, since that means most objects there’s little reason to even try to snap it to the grid. And no, you don’t need to split at 90 degree angles, you want to only split seams when you need to to avoid distortion or so that things will flatten out. Even simpler stuff would be done this way–take for instance a cylinder, you split the loop going along the length, but for the cap you can split the loop around the cap except for one edge so that it keeps the cap attached to the rest of the cylinder but still flattens out. If the cylindrical shape is really short, like those round lights on the back, then you don’t need any seams because the whole shape can be flattened and the distortion won’t be all that much.

I got you man, you’ve been a really big help to me, thanks a lot I appreciate it, one more thing about this cylinder example that you gave me, leaving the cap just connected with one edge will let some disconnected edges pretty close one with another right ??? Won’t that cause any issue ??? I mean the padding between them is going to be too short, I am working on it right now, I will post my result if you don’t mind

I wouldn’t worry about snapping a bus to a grid.
Vehicles can be stuck wherever you want to put them.

Grid snapping is for modular pieces that need to interlock to create a bigger asset.
If you made the bus in interchangeable pieces with different grills, doors, windows etc. you would want it on the grid

For the light map you definitely had way too many islands in that example.
Like Darthviper said you want as few seams and islands as possible.

I like unwrapping light maps with a pelting tool. I use UVLayoutPro by Headus.
But I saw there is something similar now in Max 2015.
There is a bunch of different tools that do Pelting I am not recommending one or the other.
Pelting is like stretching the pelt of an animals skin to make it flat
but on your UV’s. It warps the UV’s to keep in in one island.

I would not use pelting for the main texture map of a hard surface object
like that bus. But for the Lightmap channel pelting is the approach I would use.

You can make the main body of that bus into 3 islands or less.
then do separate islands for the wheels.
You can scale the unseen faces on the back of the wheels way down in size.

21k triangles is an OK resolution for desktop or console.
These days I only like to develop for Mobile.

I try to keep my entire scene under 200,000 tris so
for mobile i would look at vehicles in the 2000 to 4000 tris range.

If you are planning on selling on the asset store, why not
make 2 versions.

Here is the pelting button in Max 2015
You need to be in the Edit UV’s mode


I have never heard about pelting tool before, I saw a introduction about and seems a really cool stuff, thanks for the tip.

i did some progress yesterday and I actually have 2 island for body 2 island to the front part and every component has a single UV island, So far i,ve tested on U4 just with the automatic Layout and it has way less bleeding, today I am gonna to optimize my UV Space as much as I can and test into the engine.

Do you know if it is really necessary to have a waste space between UVs close to the borders(its called waste space I guess) ??

I still have some bleeding, I made a new layout with padding based in a grid for 32 resolution leaving 2 pixels horizontally and 1 pixel vertically, I re-scaled some small pieces but didn’t work, I have less bleeding but I have a few really bad ones

you need a higher resolution than 32 for that

I made based on 32 for the padding amount reference, on U4 I tried 512, 1024 and 2048, that is why I believe I have enough padding

You need to pack to a 30x30 grid, UE4 and UDK automatically take one pixel off each side. Also where is your bleeding?

Your UV map has lot of wasted space, and i see lot of duplicated elments that should feet in the same UV space (like tires for example).

Lightmap UVs need unique space, you cannot stack elements.

ZacD, I made 30x30 grid and this have solved 90% of my problems, I had a lot of my small components that with huge amount of bleeding now I have none, I just have a few spots of bleeding but really bad ones, I assume this is because my padding is not enough. Sorry for so many questions but I have to do it, Can one UV island bleed to itself, like in the main body Shell ???