[Radiance-general] Error: Rendering with Radiance p. 319 Luminaire Modeling

[Randolph M. Fritz]

On 2012-02-07 00:18:26 +0000, Randolph M. Fritz said:

> On 2012-02-07 00:12:18 +0000, Greg Ward said:
> 
>> Hi Randoph,
>> 
>> Could you be more specific?  The radius of a sphere whose *projected*
>> area is 1.0 for any distant point is sqrt(1/pi) as Chas derived it.
>> This is in fact what ies2rad needs.  This is not the same as a sphere
>> whose total surface area is 1.0, which is the value you derived.
>> 
>> Is there an error in ies2rad.c, somewhere?
> 
> Then maybe I've done something else wrong.  When I ran a simulation
> which checks the luminaire model against the IES file by simulating a
> goniophotometer the numbers lined up.  I'll take a closer look at my
> scripts and see if I can find a factor of two somewhere.

The same check script worked correctly with an untouched ies2rad output 
file with both the given geometry and a spherical substitute.

I then ran the procedure with -i 0.56419 and the numbers I am getting 
back are the same and correct.

I am now thoroughly confused.  Does the radius even matter in that 
procedure?  Or do I have a case of a luminaire where it doesn't matter?

Randolph

> 
> Randolph
> 
>> 
>> -Greg
>> 
>>> From: "Randolph M. Fritz" <RFritz at lbl.gov>
>>> Date: February 6, 2012 3:59:10 PM PST
>>> 
>>> I just had occasion to go through Chas. Ehrlich's luminaire modeling
>>> procedure given in *Rendering with Radiance* and there is an error on
>>> page 319 of the text. The radius of a unit sphere is 0.282095, not
>>> 0.56419. Both the number in the text and the ies2rad command are wrong.
>>> 
>>> Ouch!
>>> --
>>> Randolph M. Fritz


-- 
Randolph M. Fritz