# Remove attenuation and specify ray distance of an IES light source?

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...

···

Sent from my iPad

Bonjour,

Je suis actuellement en vacances. Je serai de retour le 7 août 2017.

En cas d'urgence, vous pouvez toujours appeler le numéro général d'Estia : +41 (0) 21/510.59.59 ou envoyer un mail à l'adresse [email protected].

Pour toutes questions relatives à DIAL+, merci d'utiliser l'adresse mail [email protected].

Cordialement

Julien Boutillier
Estia SA

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 <[email protected]>
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...

Bonjour,

Je suis actuellement en vacances. Je serai de retour le 7 août 2017.

En cas d'urgence, vous pouvez toujours appeler le numéro général d'Estia : +41 (0) 21/510.59.59 ou envoyer un mail à l'adresse [email protected].

Pour toutes questions relatives à DIAL+, merci d'utiliser l'adresse mail [email protected].

Cordialement

Julien Boutillier
Estia SA

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 <[email protected]> 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 <[email protected]>
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...

_______________________________________________
[email protected]

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 <[email protected]>
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 <[email protected]> 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 <[email protected]>
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...

Thanks Greg, thats working for me

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

···

Sent from AltaMail
From: Greg Ward <[email protected]> To: Radiance general discussion <[email protected]> Subject: Re: [Radiance-general] Remove attenuation and specify ray distance of an IES light source? Date: 17/07/2017, 22:32

From: John Everist <[email protected]>
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 <[email protected]> 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 <[email protected]>
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...

_______________________________________________