# rtrace direction

Hello everyone!

This is my first email to the group.

My queries are:

When the input to rtrace is lets say 0 0 0 0 0 1. (X,Y,Z origin = 0; X,Y,X
direction is from Up or 0 0 1) then:

1. Does it creates ONLY a single Ray from this point (0 0 0) towards
direction (0 0 1), in this case normal towards Zenith? Just to make sure I
am getting the right concepts of ray tracing.

2. If it is so, then output irradiance is from ONLY the Up direction (0 0
1), and not from any other direction?

3. If it is so, then: is it possible (may be a rarest of the rare case) to
get Zero irradiance at a point from a particular direction?

I am asking this because I am getting Zero irradiance at a vertical surface
inside the room when the direction given to rtrace is normal to this
surface. E.g for a point on North wall, the direction given is 0 -1 0. For
all the other interior surfaces I am getting some reasonable irradiance
values, but only for North wall its Zero. So my reasoning for this was,
since rtrace traces only a single ray from a point towards a particular
direction then it is possible (though rarely) to get zero irradiance from
that direction. I just thought to get your opinion on my reasoning.

All surface normals are towards inside of the room.

Thank you in anticipation! Hope I made my question clear.

Best regards,
Vaibhav Jain
www.vaibhavjain.co

Hello again!

By doing some parametric analysis I got my answer. Actually my so called
photocell was facing the window, and since I had no sky distribution (only
sun defined in my sky file), thats why in the model there was no sky
environment (just like in outer Space). Hence the recieved irradiance at
that location was Zero. I think I am right now.

Thanks!

Best regards,
Vaibhav Jain
www.vaibhavjain.co

On 21 April 2013 11:45, Vaib <[email protected]> wrote:

Hello everyone!

This is my first email to the group.

My queries are:

When the input to rtrace is lets say 0 0 0 0 0 1. (X,Y,Z origin = 0; X,Y,X
direction is from Up or 0 0 1) then:

1. Does it creates ONLY a single Ray from this point (0 0 0) towards
direction (0 0 1), in this case normal towards Zenith? Just to make sure I
am getting the right concepts of ray tracing.

2. If it is so, then output irradiance is from ONLY the Up direction (0 0
1), and not from any other direction?

3. If it is so, then: is it possible (may be a rarest of the rare case) to
get Zero irradiance at a point from a particular direction?

I am asking this because I am getting Zero irradiance at a vertical
surface inside the room when the direction given to rtrace is normal to
this surface. E.g for a point on North wall, the direction given is 0 -1 0.
For all the other interior surfaces I am getting some reasonable irradiance
values, but only for North wall its Zero. So my reasoning for this was,
since rtrace traces only a single ray from a point towards a particular
direction then it is possible (though rarely) to get zero irradiance from
that direction. I just thought to get your opinion on my reasoning.

All surface normals are towards inside of the room.

Thank you in anticipation! Hope I made my question clear.

Best regards,
Vaibhav Jain
www.vaibhavjain.co

Hi Vaibhav,

it is hard to tell what caused the result, as we do not know the
parameters you used with rtrace. For the point to be interpreted as an
irradiance sensor, which seams to be what you expect, you need the -I
switch at least.

Cheers, Lars.

Hello again!

By doing some parametric analysis I got my answer. Actually my so called
photocell was facing the window, and since I had no sky distribution
(only sun defined in my sky file), thats why in the model there was no
sky environment (just like in outer Space). Hence the recieved
irradiance at that location was Zero. I think I am right now.

Thanks!

Best regards,
Vaibhav Jain

Thanks Lars. Actually my illuminance sensor (I already used -I switch),
was spatially located on a wall, with its direction towards a window Xorg
Yorg Zorg 0 -1 0. But out of this window there was no sky glow or source
defined (neither ground); only Sun source was defined. Thats why, the
sensor was not able to trace any ray coming from that direction (0 -1 0)
using rtrace, because there was no sky. But finally I understood that and
the issue is now resolved. Also this proved to me that there is some
reverse ray tracing going on.

This was my command: echo '3 4 1.5 0 -1 0' | rtrace -w -as 512 -ar 512 -aa
0.15 -ab 2 -i+ -h sunnyScene.oct | rcalc -e
'\$1=(\$1*.265+\$2*.67+\$3*.065)*179'

Thanks again!

Vaib

PS: If you are interested to see the geometry, and sky, I have reported
that in my university assignment. Just see the 'last page' of this report:
http://tinyurl.com/d86dbo4

Best regards,
Vaibhav Jain
www.vaibhavjain.co

On 21 April 2013 23:56, Lars O. Grobe <[email protected]> wrote:

Hi Vaibhav,

it is hard to tell what caused the result, as we do not know the
parameters you used with rtrace. For the point to be interpreted as an
irradiance sensor, which seams to be what you expect, you need the -I
switch at least.

Cheers, Lars.

> Hello again!
>
> By doing some parametric analysis I got my answer. Actually my so called
> photocell was facing the window, and since I had no sky distribution
> (only sun defined in my sky file), thats why in the model there was no
> sky environment (just like in outer Space). Hence the recieved
> irradiance at that location was Zero. I think I am right now.
>
> Thanks!
>
> Best regards,
> Vaibhav Jain

_______________________________________________
[email protected]

Vaib,

There is an important difference between the -i (lower case i) and -I
(capital i) in rtrace. When -i is given, rtrace will trace a ray in the
direction given, and then will calculate the hemispherical irradiance at
the point where the ray intersects with geometry (ignoring some material
types). With the -I command it calculates the hemispherical irradiance at
the point you specify using the direction vector as a a normal for the
imaginary surface on which irradiance is calculated.

Users typically want -I, except for specialized cases. You should make
sure that -i is correct for your case.

Andy

On Mon, Apr 22, 2013 at 4:44 AM, Vaib <[email protected]> wrote:

Thanks Lars. Actually my illuminance sensor (I already used -I switch),
was spatially located on a wall, with its direction towards a window Xorg
Yorg Zorg 0 -1 0. But out of this window there was no sky glow or source
defined (neither ground); only Sun source was defined. Thats why, the
sensor was not able to trace any ray coming from that direction (0 -1 0)
using rtrace, because there was no sky. But finally I understood that and
the issue is now resolved. Also this proved to me that there is some
reverse ray tracing going on.

This was my command: echo '3 4 1.5 0 -1 0' | rtrace -w -as 512 -ar 512
-aa 0.15 -ab 2 -i+ -h sunnyScene.oct | rcalc -e
'\$1=(\$1*.265+\$2*.67+\$3*.065)*179'

Thanks again!

Vaib

PS: If you are interested to see the geometry, and sky, I have reported
that in my university assignment. Just see the 'last page' of this report:
http://tinyurl.com/d86dbo4

Best regards,
Vaibhav Jain
www.vaibhavjain.co

On 21 April 2013 23:56, Lars O. Grobe <[email protected]> wrote:

Hi Vaibhav,

it is hard to tell what caused the result, as we do not know the
parameters you used with rtrace. For the point to be interpreted as an
irradiance sensor, which seams to be what you expect, you need the -I
switch at least.

Cheers, Lars.

> Hello again!
>
> By doing some parametric analysis I got my answer. Actually my so called
> photocell was facing the window, and since I had no sky distribution
> (only sun defined in my sky file), thats why in the model there was no
> sky environment (just like in outer Space). Hence the recieved
> irradiance at that location was Zero. I think I am right now.
>
> Thanks!
>
> Best regards,
> Vaibhav Jain

_______________________________________________
[email protected]

_______________________________________________
[email protected]

Thank you Andy and Lora for correcting me and pointing this out. Since it
was my first project I was under an impression that + sign after -i makes
it equivalent to -I. Ignorance can be dangerous in simulation..
Wonderful group and spirit. Next semester I have to work much with Radiance
because it will be used in my masters thesis. So I have to start digging
deep and experiment more. Thank you again!

Vaib

On 22 April 2013 19:07, Andrew McNeil <[email protected]> wrote:

Vaib,

There is an important difference between the -i (lower case i) and -I
(capital i) in rtrace. When -i is given, rtrace will trace a ray in the
direction given, and then will calculate the hemispherical irradiance at
the point where the ray intersects with geometry (ignoring some material
types). With the -I command it calculates the hemispherical irradiance at
the point you specify using the direction vector as a a normal for the
imaginary surface on which irradiance is calculated.

Users typically want -I, except for specialized cases. You should make
sure that -i is correct for your case.

Andy

On Mon, Apr 22, 2013 at 4:44 AM, Vaib <[email protected]> wrote:

Thanks Lars. Actually my illuminance sensor (I already used -I switch),
was spatially located on a wall, with its direction towards a window Xorg
Yorg Zorg 0 -1 0. But out of this window there was no sky glow or source
defined (neither ground); only Sun source was defined. Thats why, the
sensor was not able to trace any ray coming from that direction (0 -1 0)
using rtrace, because there was no sky. But finally I understood that and
the issue is now resolved. Also this proved to me that there is some
reverse ray tracing going on.

This was my command: echo '3 4 1.5 0 -1 0' | rtrace -w -as 512 -ar 512
-aa 0.15 -ab 2 -i+ -h sunnyScene.oct | rcalc -e
'\$1=(\$1*.265+\$2*.67+\$3*.065)*179'

Thanks again!

Vaib

PS: If you are interested to see the geometry, and sky, I have reported
that in my university assignment. Just see the 'last page' of this report:
http://tinyurl.com/d86dbo4

Best regards,
Vaibhav Jain
www.vaibhavjain.co

On 21 April 2013 23:56, Lars O. Grobe <[email protected]> wrote:

Hi Vaibhav,

it is hard to tell what caused the result, as we do not know the
parameters you used with rtrace. For the point to be interpreted as an
irradiance sensor, which seams to be what you expect, you need the -I
switch at least.

Cheers, Lars.

> Hello again!
>
> By doing some parametric analysis I got my answer. Actually my so
called
> photocell was facing the window, and since I had no sky distribution
> (only sun defined in my sky file), thats why in the model there was no
> sky environment (just like in outer Space). Hence the recieved
> irradiance at that location was Zero. I think I am right now.
>
> Thanks!
>
> Best regards,
> Vaibhav Jain

_______________________________________________