[Radiance-general] Remove attenuation and specify ray distance of an IES light source?

[John Everist]

Thanks Greg, thats working for me 😊


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 From: Greg Ward <gregoryjward at gmail.com> To: Radiance general discussion <radiance-general at radiance-online.org> Subject: Re: [Radiance-general] Remove attenuation and specify ray distance of an IES light source? Date: 17/07/2017, 22:32

 
Well, you have to convert an IES source to Radiance using ies2rad, right?  Just edit the output of that program to fit the described solution.  For example, you can use the "-i" option of ies2rad to generate a spherical light source, then change the "illum" to "glow" with the Dmax limit. 
 
Cheers, 
-Greg 
 
> From: John Everist <john.everist at icloud.com> 
> Date: July 17, 2017 2:15:33 PM PDT 
>  
> Thank you greg - that's very kind of you to answer so quickly. You even managed to answer part 2 of my task before i asked it (relating to the rendered image). 
>  
> Out of curiosity, is it possible to limit the ray distance of an IES light source? 
>  
> Sent from my iPad 
>  
>> On 17 Jul 2017, at 01:11, Greg Ward <gregoryjward at gmail.com> wrote: 
>>  
>> Hi John, 
>>  
>> If I understand your query, you just want to "see" what is within a certain distance from a point -- it that right? 
>>  
>> To generate an image from the light source's perspective to some maximum distance, just use an rpict or rvu view with a fisheye view and aft clipping distance: 
>>  
>>   -vta -vp Lx Ly Lz -vh 360 -vv 360 -va Dmax 
>>  
>> Where (Lx,Ly,Lz) is the position of your light source (or just in front of it) and Dmax is how far you want to look.  You may also need the -vd and -vu specs to specify the central view direction and distance.  The above will generate a 360° fisheye view, which may be larger than you want, so adjust accordingly. 
>>  
>> If instead you want to illuminate your scene, but only for points within some distance of a source, you can use the "glow" type: 
>>  
>> void glow limited_light 
>> 0 
>> 0 
>> 4 1000 1000 1000 Dmax 
>>  
>> limited_light sphere limited_bulb 
>> 0 
>> 0 
>> 5 Lx Ly Lz 1 
>>  
>> Again, you'll need to insert the appropriate values for your source position, and this light will still have a 1/r^2 fall-off.  Also, make sure to set "-ab 0" in your rendering, so it doesn't try to count the glow source in the indirect calculation. 
>>  
>> If you want to eliminate the fall-off, you can use a compensating pattern like so: 
>>  
>> void brightfunc square_riseup 
>> 2 T*T . 
>> 0 
>> 0 
>>  
>> square_riseup glow limited_light 
>> 0 
>> 0 
>> 4 1 1 1 Dmax 
>>  
>> limited_light sphere limited_bulb 
>> 0 
>> 0 
>> 5 Lx Ly Lz 1 
>>  
>> This will still have a cosine-orientation effect on your surfaces, but no fall-off. 
>>  
>> Hope this helps. 
>> -Greg 
>>  
>>> From: John Everist <john.everist at icloud.com> 
>>> Date: July 16, 2017 4:22:51 PM PDT 
>>>  
>>> Hello community, 
>>>  
>>> Is it possible to totally break the laws of physics in radiance? Can I make a calculation with an IES file where I can terminate the ray distance (at 100 metres for example) and remove any attenuation from the rays?  
>>>  
>>> In summary, i want to use radiance to identify 'line of sight' to a maximum distance - a  point was/was not 'seen' from the light source position. 
>>>  
>>> Its properly an easy question but i cant find the answer. I have the rendering with radiance book if e answer is in there... 
 
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