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Understanding Lightmap

Hello,

I am having trouble with some lightmap issues and couldn't find a solution yet. I checked the unreal documents but couldn't understand a few things.

  • In details of an object, "Overriden Light Map Res" determines how big the map is going to be, but what about World Settings "Packed Light and Shadow Map Texture Size"? If I put 1K for both of them, does it mean there will be only one map for the selected mesh?

  • The problem I am having is a pretty common I guess. I used 1/512 formula to snap UV's to grid in Maya for my ceiling to prevent bleedings. I used the 512 res in my settings in Unreal as well. But I am having lowres shadow casts. So, are those squares in the image below represent the pixels baked into map? When I increase the 512 into 1024, they uniformly get smaller. If so, I need to put something like more then 2K to get a better result and thats huge! How do you cope with big meshes for lightmap baking?

  • One more question, I have created a day cycle which is using dynamic lightning. Do you thing I will need lightmaps or I have to disable Precomputed Lightning?

Thanks so much for your help

Lightmap 512 alt text

Lightmap 1024 alt text

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asked Apr 09 '15 at 07:38 PM in Rendering

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Excalith
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avatar image Excalith Apr 09 '15 at 08:32 PM

I have tried different things now, and I am more confused

  • I guess it is not about the resolution, but the lightning is not enough to fill the details. Am I right?

  • I lowered the resolution to 128 and it kind of blended the spots together, or vanished. Is this because of lightmap requested more data for baking with less lightning I pointed out above

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Hi Excalith,

You're on the right track with most of your thoughts with Lightmapping.

The issue you're seeing is directly related to indirect lighting from your light source and bounce.

You can see a basic example here that should help some: https://wiki.unrealengine.com/LightingTroubleshootingGuide#Why_is_there_shadow_splotches_on_my_static_mesh.3F.2C_or_How_to_clean_those_dirty_lightmaps.3F

I have created a day cycle which is using dynamic lightning. Do you thing I will need lightmaps or I have to disable Precomputed Lightning?

If you're planning to use a day/night cycle there should be no need for static lighting for the most part. There are instances where you would want to use a combination of both, but for most cases if someone makes a conscious decision to use Dynamic lighting that's because there are plans to utilize it only in that way.

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answered Apr 13 '15 at 03:51 PM

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Tim Hobson ♦♦ STAFF
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avatar image Excalith Apr 13 '15 at 04:03 PM

Hi Tim, Thank you for your help, now I understand the relation between indirect lightning, bounce and lightmaps!

I will play with new settings to see if I can make a real dynamic lightning system, but so far with my semi-dynamic setup I can't seem to update reflection capture i.e. the warm sun color reflected to metal surface stays warm even tough after day cycle it should be cold. While we are still on lightning topic, do I need more rays to update reflection capture or manually update it from BP's?

Thanks again!

avatar image Tim Hobson ♦♦ STAFF Apr 13 '15 at 06:34 PM

Reflection captures can be updated in realtime while working in the editor, but are static at runtime.

https://docs.unrealengine.com/latest/INT/Resources/Showcases/Reflections/index.html

avatar image lanfranconi Apr 13 '19 at 04:37 PM

I found this a valid question and missed an answer: "In details of an object, "Overriden Light Map Res" determines how big the map is going to be, but what about World Settings "Packed Light and Shadow Map Texture Size"? If I put 1K for both of them, does it mean there will be only one map for the selected mesh?"

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