LuxCoreRender Forums

Hi,

I'm trying to simulate realistic impression of cars lighting systems.
This sample came from http://3dmdb.com/. It's not as detailed as my final work flow will require.
Anyway, there are some results that are pretty good within a pretty little amount of time.
My approach is using real world data as much as possible...
There are some open points that I miss, respectivley that I don't know how to set them up.

1 st
I want to create a mesh light source that emits into a material. The faces that are the emitter are part of a complete solid.
The emitting direction is always toward the surface normals, right? My issue is, that I can't take the IOR of the external volume, but only the one from internal volume. Conflict comes if I have to flip my normals to emit into the material, that would turn into an external volume for lux... Did I made my point clear? I'm afraid not.

2 nd
I'd like to define the absorption of volumes by tables (tabulated data in classic lux) to ensure correct red PMMA appearance of tail lamps.

3 rd
The irregular data desciption for emitting specra is hard to use if you want to define a spectrum in 5nm steps, or even smaller.
Would it be possible to create a reference to a somehow external stored table file that is written only once and gives the necessary detail?

4 th
Why can the shadown catcher not be used in BiDir? Is there any option that the shadow catcher also catches light (road illumination).

5 th
I'm really missing the false color luminance map of classic lux, that also delivers some luminance values that could be compared with real world data or other simulation results.

Thank you

BR

Just looking at the images, it is a quite convincing result

lighting_freak wrote: ↑Thu Apr 05, 2018 5:20 pm 1 st
I want to create a mesh light source that emits into a material. The faces that are the emitter are part of a complete solid.
The emitting direction is always toward the surface normals, right?

Yes.

lighting_freak wrote: ↑Thu Apr 05, 2018 5:20 pm My issue is, that I can't take the IOR of the external volume, but only the one from internal volume. Conflict comes if I have to flip my normals to emit into the material, that would turn into an external volume for lux... Did I made my point clear? I'm afraid not.

I don't understand what do you mean with "I have to flip my normals to emit into the material". You can emit into an object, mesh, etc. but material Some kind of diagram/picture may help me to understand.

lighting_freak wrote: ↑Thu Apr 05, 2018 5:20 pm 2 nd
I'd like to define the absorption of volumes by tables (tabulated data in classic lux) to ensure correct red PMMA appearance of tail lamps.

Do you mean to define volume absorption according the wavelength ? It is possible to use the same technique used for glass dispersion in order to achieve this result however it is not a trivial work and, as usual, the problem is to find the time.

lighting_freak wrote: ↑Thu Apr 05, 2018 5:20 pm 3 rd
The irregular data desciption for emitting specra is hard to use if you want to define a spectrum in 5nm steps, or even smaller.
Would it be possible to create a reference to a somehow external stored table file that is written only once and gives the necessary detail?

You mean to add the support for reading an external text file to define "irregulardata texture" ? It is easy to add the support for this feature. I will try to add it as soon as possible, just open issue at https://github.com/LuxCoreRender/LuxCore/issues so I don't forget.

lighting_freak wrote: ↑Thu Apr 05, 2018 5:20 pm 4 th
Why can the shadown catcher not be used in BiDir? Is there any option that the shadow catcher also catches light (road illumination).

Shadow catcher is a very tricky feature and, for your application, you may need more a "light"catcher than a "shadow"catcher They are not exactly the same feature.

lighting_freak wrote: ↑Thu Apr 05, 2018 5:20 pm 5 th
I'm really missing the false color luminance map of classic lux, that also delivers some luminance values that could be compared with real world data or other simulation results.

The image pipeline contour plugin should help you (http://www.luxrender.net/forum/viewtopi ... 10#p109794). I remember to have seen B.Y.O.B to post a demo picture with the support in the new BlendLuxCore

Dade wrote: ↑Thu Apr 05, 2018 8:12 pm You mean to add the support for reading an external text file to define "irregulardata texture" ? It is easy to add the support for this feature. I will try to add it as soon as possible, just open issue at https://github.com/LuxCoreRender/LuxCore/issues so I don't forget.

This can be implemented in the addon.
It's just parsing a text file and passing the result to the existing pyluxcore properties.
This is the irregulardata node: https://github.com/LuxCoreRender/BlendL ... lardata.py
The export function does the work.

So you can decide if you want to do it in C++ in LuxCore or in Python in BlendLuxCore

For contour lines, simply go to camera imagepipeline settings and enable the contour lines button.

B.Y.O.B. wrote: ↑Thu Apr 05, 2018 9:31 pm

Dade wrote: ↑Thu Apr 05, 2018 8:12 pm You mean to add the support for reading an external text file to define "irregulardata texture" ? It is easy to add the support for this feature. I will try to add it as soon as possible, just open issue at https://github.com/LuxCoreRender/LuxCore/issues so I don't forget.

This can be implemented in the addon.
It's just parsing a text file and passing the result to the existing pyluxcore properties.
This is the irregulardata node: https://github.com/LuxCoreRender/BlendL ... lardata.py
The export function does the work.

So you can decide if you want to do it in C++ in LuxCore or in Python in BlendLuxCore

It may be better to have it in LuxCore so it can be used by any app ... I have the feeling I should have said that

Dade wrote: ↑Thu Apr 05, 2018 8:12 pm Shadow catcher is a very tricky feature and, for your application, you may need more a "light"catcher than a "shadow"catcher They are not exactly

This is what may be very interesting for you:

1) place the camera over the car looking down, perpendicular to the road;

2) mark all the car as camera invisible;

3) render with contour lines;

You should get something like this, with contour lines (and without the car):

Hi,

thanks for that lots of answers.

I don't understand what do you mean with "I have to flip my normals to emit into the material". You can emit into an object, mesh, etc. but material Some kind of diagram/picture may help me to understand.

First I'll try to describe the issue in a better way: So light is emitted into a volume. I can't change the IOR reference to the external volume.
If I use the "normal" setup the IOR refence is coming from the internal volume (which I can't use in that case.)
Anyway, the easiest (and in my opinion most logical) solution might be an option to emit light against the surface normals.

Shadow catcher is a very tricky feature and, for your application, you may need more a "light"catcher than a "shadow"catcher They are not exactly the same feature.

Yes, light and shadow catcher would be the required functions.

My request popped up after seeing this thread in "old" forum:
http://www.luxrender.net/forum/viewtopi ... automotive

I'm wondering whether I could integrate the model perfectly into an HDRI environmel (something ground plane projection of the HDRI image) and create also light (and shadow) interactions with this surroundings.

The image pipeline contour plugin should help you

From it's name its "irradience" (assuming that illuminace is meant it means lux-values) but I'm looking for luminance (in cd/m² - units).
Classic GUI offerd a feature that turns the rendered image into a virtual luminance camera shot. That was a great feature.

In the particular case of rendering the daytime running light of a car the road view doesn't make sense, but for low and high beam functions it's working pretty well. I've done several analysis and animations using the "old" classic lux.

Once more, thanks for all your help and support.

BR

lighting_freak wrote: ↑Fri Apr 06, 2018 5:31 pm So light is emitted into a volume.
I can't change the IOR reference to the external volume.
If I use the "normal" setup the IOR refence is coming from the internal volume (which I can't use in that case.)
Anyway, the easiest (and in my opinion most logical) solution might be an option to emit light against the surface normals.

It is veeeeery easy to add an option to emit light in the opposite direction but I don't think it is really required. This is how I would model your object:
I would model the red mesh with a not emitting material and an outside volume with IOR 1.0 (i.e. air) and an inside volume with IOR 1.4 (i.e. glass or whatever).

I would model the green mesh with an emitting material and a normal pointing inside. An outside volume with IOR of 1.4 and an inside volume IOR of 1.0 (see what I did ? I flipped the volumes, not only the normal).

Yes, the 2 meshes are open and this can be very dangerous with volumes but the result is still a coherent and correct object.

Hi,

finished a first quick animation of that car. Looks nice. Each picture is done with 50 samples BiDir only.
Complete animation uses 300 frames. I think the reported issue in this thread can be closed now. The renders ran perfectly. Thank you.
viewtopic.php?f=4&t=195

I would model the green mesh with an emitting material and a normal pointing inside. An outside volume with IOR of 1.4 and an inside volume IOR of 1.0 (see what I did ? I flipped the volumes, not only the normal).

How can a some more complex volumes be treaten that can't be defined with a single IOR-only?
I assume that using the internal volume IOR transfers the complex IOR definitions of the volume towards the material definition.
I still think that there might be a "flip emission direction" button that solves the issue in most logical way, without mind twists.
BR

EDIT:
I forgot to tell you how to handle the attachments. Sorry.
Please download all the zip files.
Remove the last ".zip" from it's name, now it's a splitted zip file.
This file can be unzipped with e.g. 7zip.
The result should be a few seconds video in mp4 format.

lighting_freak wrote: ↑Sun Apr 08, 2018 10:26 am

I would model the green mesh with an emitting material and a normal pointing inside. An outside volume with IOR of 1.4 and an inside volume IOR of 1.0 (see what I did ? I flipped the volumes, not only the normal).

How can a some more complex volumes be treaten that can't be defined with a single IOR-only?
I assume that using the internal volume IOR transfers the complex IOR definitions of the volume towards the material definition.

You can leverage volume priorities, it is a quite advanced features not many renders support and, for instance, it allows to easily embed a volume inside another one.

Hi,

did I got you right? I shall create the emitting surface inside the volume.
This means that internal and external volume is the same and I can reference to the more complex volume definition as well.
How would you add those priorities that you've mentioned.

Well yes, it may work... but sounds a little bit like bypassing, not solving, an issue.

BR.