modeling trees in Radiance

radiance-general
1

Dear list,

May I ask advices on modeling trees in a Radiance scene?

Suppose I can get a so-called "*transmittance coefficient*" value for a
given type of tree through field measurement and then calculating the
average ratio of the irradiance below a tree to that above it for multiple
points below a tree under various types of sky conditions, what *surface
parameter * can I specify in Radiance for a simplified sphere surface
representing a tree that can use this "transmittance coefficient" as a
reference for simulation to understand the impact of the tree to the
surrounding environment in terms of shading?

Hope I explain myself clearly ...

Thanks!

2

Hi Joe,

If you want to model your tree as a sphere (on a stick?) with a certain transmittance, the "trans" material type should suit your purpose. Parameter setting is a bit tricky, but since you don't have any reflection or scattering to consider, simply set values according to your transmittance T:

void trans treeT
0
0
7 T T T 0 0 1 1

I hope this addresses your question.

Best,
-Greg

···

From: Joe Smith <[email protected]>
Subject: [Radiance-general] modeling trees in Radiance
Date: February 5, 2015 3:41:24 AM EST

Dear list,

May I ask advices on modeling trees in a Radiance scene?

Suppose I can get a so-called "transmittance coefficient" value for a given type of tree through field measurement and then calculating the average ratio of the irradiance below a tree to that above it for multiple points below a tree under various types of sky conditions, what surface parameter can I specify in Radiance for a simplified sphere surface representing a tree that can use this "transmittance coefficient" as a reference for simulation to understand the impact of the tree to the surrounding environment in terms of shading?

Hope I explain myself clearly ...

Thanks!

3

Dear Joe and Greg,

Not sure if this is a question... there it goes though.

I was trying to emulate a micro perforated metal the other day (I do not
want to draw thousands of little holes!)... I tried to use TRANS equations
to derive the parameters I needed, but it did not seem to work. I think
TRANS properties vary with the angle of incidence?? (the percentaje of
specular transmission does no change with different angles of incidence in
a perforated screen)

I ended up using a mixture between VOID and a Plastic material, on which I
varied the percentage of "Void"... I am not sure, maybe that trick would
also help modelling trees.

Am I correct? Is, what I did, legally from the physical laws of lighitng?

THANKS

Germán

···

2015-02-05 8:52 GMT-03:00 Greg Ward <[email protected]>:

Hi Joe,

If you want to model your tree as a sphere (on a stick?) with a certain
transmittance, the "trans" material type should suit your purpose.
Parameter setting is a bit tricky, but since you don't have any reflection
or scattering to consider, simply set values according to your
transmittance T:

void trans treeT
0
0
7 T T T 0 0 1 1

I hope this addresses your question.

Best,
-Greg

*From: *Joe Smith <[email protected]>

*Subject: *[Radiance-general] modeling trees in Radiance

*Date: *February 5, 2015 3:41:24 AM EST

Dear list,

May I ask advices on modeling trees in a Radiance scene?

Suppose I can get a so-called "*transmittance coefficient*" value for a
given type of tree through field measurement and then calculating the
average ratio of the irradiance below a tree to that above it for multiple
points below a tree under various types of sky conditions, what *surface
parameter * can I specify in Radiance for a simplified sphere surface
representing a tree that can use this "transmittance coefficient" as a
reference for simulation to understand the impact of the tree to the
surrounding environment in terms of shading?

Hope I explain myself clearly ...

Thanks!

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

4

Dear Joe and Greg,

I was trying to emulate a micro perforated metal the other day (I do not
want to draw thousands of little holes!)... I tried to use TRANS equations
to derive the parameters I needed, but it did not seem to work. I think
TRANS properties vary with the ngle of incidence??

I ended up using a mixture between VOID and a Plastic material, on which I
varied the percentage of "Void"... I am not sure, maybe that trick would
also help modelling trees.

Am I correct? Is, what I did, legally from the physical laws of lighitng?
Hi Joe,

If you want to model your tree as a sphere (on a stick?) with a certain
transmittance, the "trans" material type should suit your purpose.
Parameter setting is a bit tricky, but since you don't have any reflection
or scattering to consider, simply set values according to your
transmittance T:

void trans treeT
0
0
7 T T T 0 0 1 1

I hope this addresses your question.

Best,
-Greg

···

*From: *Joe Smith <[email protected]>

*Subject: *[Radiance-general] modeling trees in Radiance

*Date: *February 5, 2015 3:41:24 AM EST

Dear list,

May I ask advices on modeling trees in a Radiance scene?

Suppose I can get a so-called "*transmittance coefficient*" value for a
given type of tree through field measurement and then calculating the
average ratio of the irradiance below a tree to that above it for multiple
points below a tree under various types of sky conditions, what *surface
parameter * can I specify in Radiance for a simplified sphere surface
representing a tree that can use this "transmittance coefficient" as a
reference for simulation to understand the impact of the tree to the
surrounding environment in terms of shading?

Hope I explain myself clearly ...

Thanks!

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

5

I think German's proposal is very clever for modelling a tree canopy "material". But if Joe is then using spheres for modelling the trees geometry, then the void percentage must be set to the square root of the tree canopy transmittance since a ray "transmitted" by the tree will always intersect twice with the sphere!

I hope this will help.

Raphaël

6

I see Raphaël just pointed out what I was in the middle of typing about the square root transmittance correction. Also, keep in mind this will only be a very rough approximation for any measurements very near the tree, where rays passing through all parts of the tree get the same reduction even if they just glance the fringe of the sphere or other shape. In reality, rays passing through the outer fringes of a tree canopy would intersect with fewer leaves than those passing through the more substantial core of the tree (also depending on tree species).
I would love to here if anyone has a more ideal solution for modeling trees that is relatively accurate, and reasonable in terms of rendering time and use of RAM – in other words without modeling every single leaf. If it looked nice that would be a bonus. Is this a possible application for something exotic like mist? I’ve never even investigated mist so apologies if that’s a ridiculous suggestion.

···

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1 Like
7

Yes, I should have thought about the square root -- good catch!

The trans type doesn't change with incident angle (unlike glass or dielectric), which is part of why I suggested it. I don't know what's happening in Germán's case, but using a mixfunc with void and plastic is a perfectly acceptable approach.

As for varying the absorption using mist, a ball of mist might indeed have the desired behavior, as the absorption is an exponential function of the volume traversed using the mist material.

Cheers,
-Greg

···

From: Christopher Rush <[email protected]>
Subject: Re: [Radiance-general] modeling trees in Radiance
Date: February 5, 2015 7:05:02 AM PST

I see Raphaël just pointed out what I was in the middle of typing about the square root transmittance correction. Also, keep in mind this will only be a very rough approximation for any measurements very near the tree, where rays passing through all parts of the tree get the same reduction even if they just glance the fringe of the sphere or other shape. In reality, rays passing through the outer fringes of a tree canopy would intersect with fewer leaves than those passing through the more substantial core of the tree (also depending on tree species).

I would love to here if anyone has a more ideal solution for modeling trees that is relatively accurate, and reasonable in terms of rendering time and use of RAM – in other words without modeling every single leaf. If it looked nice that would be a bonus. Is this a possible application for something exotic like mist? I’ve never even investigated mist so apologies if that’s a ridiculous suggestion.

1 Like
8

Dear all, thank you very much!

To Greg: May I ask, if I also want to consider reflection or scattering of
the sphere surface, how should I specify the parameters for the trans type
of material? and what does the "trans" parameter for trans material means?

To German: Thank you for the tip of using a mixfunc! Can you advise on how
to specify the funcfile to define the pattern and proportion of mixing of
void and plastic materials?

To Compagnon: Thank you for the square-root reminder!

To Christopher and Greg: Thanks for the tip on mist! Can we imagine the
tree object modeled in this way as a hollowed sphere whose surface is
composed of a texture with an "alternating void and plastic" pattern, and
the inside of the sphere is filled with a lump of "mysterious" fog ...?

···

On Fri, Feb 6, 2015 at 8:14 AM, Greg Ward <[email protected]> wrote:

Yes, I should have thought about the square root -- good catch!

The trans type doesn't change with incident angle (unlike glass or
dielectric), which is part of why I suggested it. I don't know what's
happening in Germán's case, but using a mixfunc with void and plastic is a
perfectly acceptable approach.

As for varying the absorption using mist, a ball of mist might indeed have
the desired behavior, as the absorption is an exponential function of the
volume traversed using the mist material.

Cheers,
-Greg

*From: *Christopher Rush <[email protected]>

*Subject: *Re: [Radiance-general] modeling trees in Radiance

*Date: *February 5, 2015 7:05:02 AM PST

   I see Raphaël just pointed out what I was in the middle of typing
about the square root transmittance correction. Also, keep in mind this
will only be a very rough approximation for any measurements very near the
tree, where rays passing through all parts of the tree get the same
reduction even if they just glance the fringe of the sphere or other shape.
In reality, rays passing through the outer fringes of a tree canopy would
intersect with fewer leaves than those passing through the more substantial
core of the tree (also depending on tree species).

I would love to here if anyone has a more ideal solution for modeling
trees that is relatively accurate, and reasonable in terms of rendering
time and use of RAM – in other words without modeling every single leaf. If
it looked nice that would be a bonus. Is this a possible application for
something exotic like mist? I’ve never even investigated mist so apologies
if that’s a ridiculous suggestion.

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

9

Ok, so I can think of two ways... one sort of show "random leaves", and the
other is just continuous. HERE
<https://drive.google.com/open?id=0B2NfkTSl19hQNjZUOGZzTkZSTjA&authuser=0>
is a picture of both. I guess the one that shows leaves is better, and
allows more interesting stuff... also, since it is random, I assume its is
also more realistic.

HERE IS THE FOLDER
<https://drive.google.com/open?id=0B2NfkTSl19hQVHpKSmFRSFdNcXc&authuser=0>
with the files... just run the "run" file, and you will get everyting done.

Best,

Germán

···

2015-02-06 5:55 GMT-03:00 Joe Smith <[email protected]>:

Dear all, thank you very much!

To Greg: May I ask, if I also want to consider reflection or scattering of
the sphere surface, how should I specify the parameters for the trans type
of material? and what does the "trans" parameter for trans material means?

To German: Thank you for the tip of using a mixfunc! Can you advise on how
to specify the funcfile to define the pattern and proportion of mixing of
void and plastic materials?

To Compagnon: Thank you for the square-root reminder!

To Christopher and Greg: Thanks for the tip on mist! Can we imagine the
tree object modeled in this way as a hollowed sphere whose surface is
composed of a texture with an "alternating void and plastic" pattern, and
the inside of the sphere is filled with a lump of "mysterious" fog ...?

On Fri, Feb 6, 2015 at 8:14 AM, Greg Ward <[email protected]> wrote:

Yes, I should have thought about the square root -- good catch!

The trans type doesn't change with incident angle (unlike glass or
dielectric), which is part of why I suggested it. I don't know what's
happening in Germán's case, but using a mixfunc with void and plastic is a
perfectly acceptable approach.

As for varying the absorption using mist, a ball of mist might indeed
have the desired behavior, as the absorption is an exponential function of
the volume traversed using the mist material.

Cheers,
-Greg

*From: *Christopher Rush <[email protected]>

*Subject: *Re: [Radiance-general] modeling trees in Radiance

*Date: *February 5, 2015 7:05:02 AM PST

   I see Raphaël just pointed out what I was in the middle of typing
about the square root transmittance correction. Also, keep in mind this
will only be a very rough approximation for any measurements very near the
tree, where rays passing through all parts of the tree get the same
reduction even if they just glance the fringe of the sphere or other shape.
In reality, rays passing through the outer fringes of a tree canopy would
intersect with fewer leaves than those passing through the more substantial
core of the tree (also depending on tree species).

I would love to here if anyone has a more ideal solution for modeling
trees that is relatively accurate, and reasonable in terms of rendering
time and use of RAM – in other words without modeling every single leaf. If
it looked nice that would be a bonus. Is this a possible application for
something exotic like mist? I’ve never even investigated mist so apologies
if that’s a ridiculous suggestion.

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

10

Hi Joe,

The setting of trans parameters is a bit tricky and an oft-visited question that should be the first in a FAQ, if indeed such a thing will happen if it hasn't yet after 25 years.... If you do a search on the Radiance mailing list for "trans parameters" or similar, I'm sure you'll find some choice entries. Maybe someone can recommend a calculator for you, but the basic formulae are given in Section 5.2 on p. 325-6 of "Rendering with Radiance," attached below.

I like the concept of using a mixfunc with void and plastic on the outside and mist on the inside. Working out the appropriate parameters to get a reasonable look would be a challenge, but the results might be worth it.

Best,
-Greg

TransMaterial.pdf (80 KB)

···

From: Joe Smith <[email protected]>
Subject: Re: [Radiance-general] modeling trees in Radiance
Date: February 6, 2015 12:55:47 AM PST

Dear all, thank you very much!

To Greg: May I ask, if I also want to consider reflection or scattering of the sphere surface, how should I specify the parameters for the trans type of material? and what does the "trans" parameter for trans material means?

To German: Thank you for the tip of using a mixfunc! Can you advise on how to specify the funcfile to define the pattern and proportion of mixing of void and plastic materials?

To Compagnon: Thank you for the square-root reminder!

To Christopher and Greg: Thanks for the tip on mist! Can we imagine the tree object modeled in this way as a hollowed sphere whose surface is composed of a texture with an "alternating void and plastic" pattern, and the inside of the sphere is filled with a lump of "mysterious" fog ...?

On Fri, Feb 6, 2015 at 8:14 AM, Greg Ward <[email protected]> wrote:
Yes, I should have thought about the square root -- good catch!

The trans type doesn't change with incident angle (unlike glass or dielectric), which is part of why I suggested it. I don't know what's happening in Germán's case, but using a mixfunc with void and plastic is a perfectly acceptable approach.

As for varying the absorption using mist, a ball of mist might indeed have the desired behavior, as the absorption is an exponential function of the volume traversed using the mist material.

Cheers,
-Greg

From: Christopher Rush <[email protected]>
Subject: Re: [Radiance-general] modeling trees in Radiance
Date: February 5, 2015 7:05:02 AM PST

I see Raphaël just pointed out what I was in the middle of typing about the square root transmittance correction. Also, keep in mind this will only be a very rough approximation for any measurements very near the tree, where rays passing through all parts of the tree get the same reduction even if they just glance the fringe of the sphere or other shape. In reality, rays passing through the outer fringes of a tree canopy would intersect with fewer leaves than those passing through the more substantial core of the tree (also depending on tree species).

I would love to here if anyone has a more ideal solution for modeling trees that is relatively accurate, and reasonable in terms of rendering time and use of RAM – in other words without modeling every single leaf. If it looked nice that would be a bonus. Is this a possible application for something exotic like mist? I’ve never even investigated mist so apologies if that’s a ridiculous suggestion.

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general