On 09/21/2017 06:15 AM, Ive wrote:
> Am 9/20/2017 um 9:40 schrieb Mr:
> 
> They are but the effect is too dim to be seen in this image.
> While the headlights itself are modeled quite detailed and realistic I 
> don't think it is possible to get realistic head*lights* without using 
> IES light profiles, something POV-Ray does not support.
> 
> -Ive

I remember the VW van and bug headlights in the VWs of my youth as being 
VERY dim and so thought you'd gotten them about right for the environment!

On the IES profiles. I took a run at some kind of support 5 years or 
more back on a mention of them in the newsgroups - prior to which I 
didn't know such files existed. Does a profile actually exist for a 
1970s VW van headlight? ;-)

Perhaps it was unfortunate choices in light fixture manufactures and IES 
profiles, but with the samples I grabbed, I ended frustrated by the 
differing standards over time, the seeming lack of full compliance to 
any of them and the frequent, probable errors in the data. A task that 
started simple per first look, turned into real work with a view to 
endless support. I quit. I got to where I was able to render a few 
reasonable looking IES profiles via light enclosing, hollow spheres with 
image mapped transparency(1).

Today, are the other rendering tools supporting real IES manufacturer 
profiles (if so, what does that really mean...(3)) or are they using 
some already converted set of spot light like variations for a 
particular tool or standard being 'called' IES lights in the tool? I'm 
thinking it easier to support the latter sort of 'IES stand-in' in 
POV-Ray as that could perhaps be a smallish set of spherical image maps 
folks could use in some semi-standard light enclosing set up?

Bill P.

(1) - Passable for most, essentially spreading, IES intensity profiles 
such as a light and fixture against a building's siding say. This faking 
is not OK for light&fixture profiles which have focusing or additive 
areas as one moves away from the light in 3D. Such faking as that needs 
more complicated, light associated, 3D pigments/media densities for all 
objects and media around the light(s). This too is doable with functions 
or DF3s/functions in POV-Ray and it'd now be easier with function based 
user_defined {} pigments in 3.8. Though not IES related, I've played 
with projected_through no_image-isosurface-fragments as a way to shape 
3d scene light intensity in interesting ways not requiring modification 
to in scene textures / media. Maybe such a technique could play an IES 
roll too...

The IES files contain a smallish number of samples taken around a 
certain light source and light fixture which get interpolated for the 
resultant, in scene, profile.

To 'accurately' model a light(2) and fixture one must shoot photons from 
a light source inside a good representation of the actual light fixture 
- perhaps also calibrate/fit to actual IES measured locations for the 
fixture. I'd argue POV-Ray can implement the photons method quite well - 
if one wants to burn the time and effort for the precise effect.

(2) - As you know, you need too some overall system like lightsys 
(spectral rendering?) for the sources and intensities indicated in the 
IES file about which you know far, far more than me :-).

(3) - For one, does such implementation grab too the light fixture's 
model? Asking because in my very limited bit of playing, I had trouble 
with the environment corrupting the result of the IES profiled light due 
not having the actual fixture (parts corresponding to 
black/blocked-by-the-fixture light of the profile). This was partly me 
not being able to easily sort out good sphere enclosed light position 
and orientations relative to the fixture given the actual light bulb's 
shape was not the shape of my spherical stand-in. All caused me to 
wonder whether folks using IES profiles were just after some rough 
effect more than any kind of exact one. If so, maybe the format issues 
don't matter all that much and sometimes sloppy IES files - so long as 
you can parse and interpret them somehow - are OK in practice. Or, maybe 
the IES implementation in other tools is much different than anything I 
considered?

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