[Radiance-general] IES files and MGF geometry

[Axel Jacobs]

Hello again,

I've run some quick tests on with my bollard photometry. falsecolor
images below:

Unaltered IES file as it came from the manufacturer:
http://www.jaloxa.eu/pickup/mr84_li34_fc.jpg
This uses a short, capped cylinder.  rvu complains about
"source aspect too small for cylinder xxx
aiming failure for light source xxx"
Looks weird.

sphere, generated with ies2rad's -i option:
http://www.jaloxa.eu/pickup/mr84_li34_sphere_fc.jpg
This is a little darker than the previous image.

box geometry with all 6 sides (edited IES file):
http://www.jaloxa.eu/pickup/mr84_li34_closed_box_fc.jpg
some 'streaky' artifacts that didn't show up in the sphere image.

box with top and bottom removed. Unaltered source.cal
http://www.jaloxa.eu/pickup/mr84_li34_open_box_fc.jpg
a little darker than the full box

box with top and bottom removed.  source.cal edited as per Greg's instructions
http://www.jaloxa.eu/pickup/mr84_li34_open_box_fixed_fc.jpg
Looks identical to the previous picture.

I used the new ltview command for the previews, so the lower side of
the enclosing plane is much further away than the actual ground would
be.  This might be the reason why the 'corrected' and 'uncorrected'
open boxes produce the same results.  Equally, there is hardly any
downward or upward component.  Virtually all of the emitted light is
projected into a narrow strip.  It still seems as if the open box does
emit a little less light than its closed brother, even with the
correction in source.cal

Best
Axel





On 5 November 2014 17:19, Axel Jacobs <jacobs.axel at gmail.com> wrote:
> Thanks, Greg.  Will give this a try.
>
> Best
> Axel
>
>
> On 5 November 2014 17:04, Greg Ward <gregoryjward at gmail.com> wrote:
>> Hi Axel,
>>
>> Yes, as Randolph reminds me, LM-63 did have the geometry spec in there.  All I remember is that it was never supported by anyone.  At least we are using MGF in our XML specification for complex fenestration system BSDFs, so it's not a complete waste.
>>
>> Regarding the local box correction, you could take out the third term "noneg(abs(Pz-Dz*Ts)-A4/2)*A2*A3" from the formula:
>>
>> lboxprojection = (      noneg(abs(Px-Dx*Ts)-A2/2)*A3*A4 +
>>                         noneg(abs(Py-Dy*Ts)-A3/2)*A2*A4 +
>>                         noneg(abs(Pz-Dz*Ts)-A4/2)*A2*A3 ) / Ts;
>>
>> I think that should work.
>>
>> Cheers,
>> -Greg
>>
>>> From: Axel Jacobs <jacobs.axel at gmail.com>
>>> Subject: Re: [Radiance-general] IES files and MGF geometry
>>> Date: November 5, 2014 8:57:01 AM PST
>>>
>>> Hi Greg,
>>>
>>> I only know about this MGF embedding from the ies2rad man page, and
>>> thought it might solve my problem:
>>>
>>> " -i rad    Ignore the crude geometry given by the IES input file and
>>> use  instead  an  illum
>>>                 sphere  with radius rad.  This option may be useful
>>> when the user wishes to add a
>>>                 more accurate geometric description to the light
>>> source model, though  this  need
>>>                 is  obviated by the recent LM-63-1995 specification,
>>> which uses MGF detail geome-
>>>                 try.  (See -g option below.)"
>>>
>>> This sounds rather more positive than the situation appears to be now.  Oh well.
>>>
>>> As you say--I would need near-field for my bollard.  Thank for sending
>>> the projection formula.  With the NF-correction for boxes already in
>>> the code, would a square bollard (again w/o bottom and top) be any
>>> easier to describe?  A square imposter is still a lot better than a
>>> hovering crystal ball.
>>>
>>> Many thanks
>>>
>>> Best
>>> Axel
>>
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