# Cubical sky maps?

Anyone using these? Anyone think these might be possible?

···

--
Randolph Fritz • RFritz@lbl.gov
Environmental Energy Technologies Division • Lawrence Berkeley Labs

Should be possible, but why give up the advantages of the dimensionless source-object? With cubical maps you must think about where in you cube the scene is to be located, how much related error to accept, then, how to get the increased scene bounding box reflected in the ambient setting...

Cheers, Lars.

···

On 11.06.2010 18:57, R Fritz wrote:

Anyone using these? Anyone think these might be possible?

Thanks, Lars. The big reason for doing this is to make it possible to use a captured sky, and it's probably easier to keep the exterior housing containing cameras clean if it's got flat surfaces, than if it's a sphere.

···

On 2010-06-12 02:41:27 -0700, Lars O. Grobe said:

On 11.06.2010 18:57, R Fritz wrote:

Anyone using these? Anyone think these might be possible?

Should be possible, but why give up the advantages of the dimensionless source-object? With cubical maps you must think about where in you cube the scene is to be located, how much related error to accept, then, how to get the increased scene bounding box reflected in the ambient setting...

--
Randolph Fritz • RFritz@lbl.gov
Environmental Energy Technologies Division • Lawrence Berkeley Labs

Using a cube map and actually mapping a cube are separable issues. You don't need local geometry to do this in other words. The mapping, which you can translate pretty easily to a .cal file, is given in Paul Debevec's image-based lighting chapter in the HDR Imaging book, Section 9.4.4. Quoting:

World to Image:
if Dz<0 and Dz<Dx and Dz<Dy
u = 1.5 - 0.5 * Dx / Dz
v = 2.5 - 0.5 * Dy / Dz
else if Dz>0 and Dz>Dx and Dz>Dy
u = 1.5 + 0.5 * Dx / Dz
v = 0.5 + 0.5 * Dy / Dz
else if Dy<0 and Dy<Dx and Dy<Dz
u = 1.5 + 0.5 * Dx / Dy
v = 1.5 - 0.5 * Dz / Dy
else if Dy>0 and Dy>Dx and Dy>Dz
u = 1.5 + 0.5 * Dx / Dy
v = 3.5 + 0.5 * Dz / Dy
else if Dx<0 and Dx<Dy and Dx<Dz
u = 0.5 - 0.5 * Dz / Dx
v = 2.5 + 0.5 * Dy / Dx
else if Dx>0 and Dx>Dy and Dx>Dz
u = 2.5 + 0.5 * Dz / Dx
v = 2.5 + 0.5 * Dy / Dx

Image to World:
if u>=1 and u <=2 and v>=0 and v<=1 // up
Vx = (u - 0.5) * 6
Vy = 1.0
Vz = (v - 0.125) * -8
else if u>=0 and u <=1 and v>=1 and v<=2 // left
Vx = -1.0;
Vy = (v - 0.375) * -8;
Vz = (u – 1/6) * -6;
else if u>=1 and u <=2 and v>=1 and v<=2 // forward
Vx = (u - 0.5) * 6;
Vy = (v - 0.375) * -8;
Vz = -1.0;
else if u>=2 and u <=3 and v>=1 and v<=2 // right
Vx = 1.0;
Vy = (v - 0.375) * -8;
Vz = (u – 5/6) * 6;
else if u>=1 and u <=2 and v>=2 and v<=4 // down
Vx = (u - 0.5) * 6;
Vy = -1.0;
Vz = (v - 0.625) * 8;
else if u>=1 and u <=2 and v>=3 and v<=4 // backward
Vx = (u - 0.5) * 6;
Vy = (v - 0.875) * 8;
Vz = 1.0;
normalize = 1 / sqrt(Vx * Vx + Vy * Vy + Vz * Vz)
Dx = normalize* Vx
Dy = normalize* Vy
Dz = normalize* Vz

Best,
-Greg

···

From: R Fritz <RFritz@lbl.gov>
Date: June 13, 2010 7:56:16 AM PDT

On 2010-06-12 02:41:27 -0700, Lars O. Grobe said:

On 11.06.2010 18:57, R Fritz wrote:

Anyone using these? Anyone think these might be possible?

Should be possible, but why give up the advantages of the dimensionless source-object? With cubical maps you must think about where in you cube the scene is to be located, how much related error to accept, then, how to get the increased scene bounding box reflected in the ambient setting...

Thanks, Lars. The big reason for doing this is to make it possible to use a captured sky, and it's probably easier to keep the exterior housing containing cameras clean if it's got flat surfaces, than if it's a sphere.

Thanks, Lars. The big reason for doing this is to make it possible to
use a captured sky, and it's probably easier to keep the exterior
housing containing cameras clean if it's got flat surfaces, than if it's
a sphere.

I would be careful with that. If you have a dome with a wide-angle camera, transmission is about perpendicular for all directions. If you have a flat glass, it is not. Do you want to a cube-shaped box with five cameras?

Cheers, Lars.

Randolph's query reminded me that I had a search for cheap domes a while ago. This is what I found:

http://www.hammacher.com/publish/75098.asp?cm_mmc=CJ--1414665--1492714-_-Hammacher+Schlemmer

Difficult to tell from the photo if it is optically suitable, though Fido looks quite happy. I'd be interested to hear if this is any good as a housing.

Woof woof!

-John

···

-----------------------------------------------
Dr. John Mardaljevic
Institute of Energy and Sustainable Development
De Montfort University
The Gateway
Leicester
LE1 9BH, UK
+44 (0) 116 257 7972
+44 (0) 116 257 7981 (fax)

Oh, cool.

Thanks!

Randolph

···

On 2010-06-13 09:13:34 -0700, Greg Ward said:

Using a cube map and actually mapping a cube are separable issues. You don't need local geometry to do this in other words. The mapping,
which you can translate pretty easily to a .cal file, is given in Paul
Debevec's image-based lighting chapter in the HDR Imaging book,Section 9.4.4. Quoting:

World to Image:
if Dz<0 and Dz<Dx and Dz<Dy
u = 1.5 - 0.5 * Dx / Dz
v = 2.5 - 0.5 * Dy / Dz
else if Dz>0 and Dz>Dx and Dz>Dy
u = 1.5 + 0.5 * Dx / Dz
v = 0.5 + 0.5 * Dy / Dz
else if Dy<0 and Dy<Dx and Dy<Dz
u = 1.5 + 0.5 * Dx / Dy
v = 1.5 - 0.5 * Dz / Dy
else if Dy>0 and Dy>Dx and Dy>Dz
u = 1.5 + 0.5 * Dx / Dy
v = 3.5 + 0.5 * Dz / Dy
else if Dx<0 and Dx<Dy and Dx<Dz
u = 0.5 - 0.5 * Dz / Dx
v = 2.5 + 0.5 * Dy / Dx
else if Dx>0 and Dx>Dy and Dx>Dz
u = 2.5 + 0.5 * Dz / Dx
v = 2.5 + 0.5 * Dy / Dx

Image to World:
if u>=1 and u <=2 and v>=0 and v<=1 // up
Vx = (u - 0.5) * 6
Vy = 1.0
Vz = (v - 0.125) * -8
else if u>=0 and u <=1 and v>=1 and v<=2 // left
Vx = -1.0;
Vy = (v - 0.375) * -8;
Vz = (u – 1/6) * -6;
else if u>=1 and u <=2 and v>=1 and v<=2 // forward
Vx = (u - 0.5) * 6;
Vy = (v - 0.375) * -8;
Vz = -1.0;
else if u>=2 and u <=3 and v>=1 and v<=2 // right
Vx = 1.0;
Vy = (v - 0.375) * -8;
Vz = (u – 5/6) * 6;
else if u>=1 and u <=2 and v>=2 and v<=4 // down
Vx = (u - 0.5) * 6;
Vy = -1.0;
Vz = (v - 0.625) * 8;
else if u>=1 and u <=2 and v>=3 and v<=4 // backward
Vx = (u - 0.5) * 6;
Vy = (v - 0.875) * 8;
Vz = 1.0;
normalize = 1 / sqrt(Vx * Vx + Vy * Vy + Vz * Vz)
Dx = normalize* Vx
Dy = normalize* Vy
Dz = normalize* Vz

Best,
-Greg

From: R Fritz <RFritz@lbl.gov>
Date: June 13, 2010 7:56:16 AM PDT

On 2010-06-12 02:41:27 -0700, Lars O. Grobe said:

On 11.06.2010 18:57, R Fritz wrote:

Anyone using these? Anyone think these might be possible?

Should be possible, but why give up the advantages of the>> dimensionless source-object? With cubical maps you must think about

where in you cube the scene is to be located, how much related>> error to accept, then, how to get the increased scene bounding box

reflected in the ambient setting...

Thanks, Lars. The big reason for doing this is to make it possible> to use a captured sky, and it's probably easier to keep the exterior

housing containing cameras clean if it's got flat surfaces, than if

it's a sphere.

--
Randolph Fritz • RFritz@lbl.gov
Environmental Energy Technologies Division • Lawrence Berkeley Labs

That was actually pretty much what I was visualizing. Any model, we'd have to experiment.

Randolph

···

On 2010-06-14 07:35:58 -0700, Lars O. Grobe said:

Thanks, Lars. The big reason for doing this is to make it possible to
use a captured sky, and it's probably easier to keep the exterior
housing containing cameras clean if it's got flat surfaces, than if it's
a sphere.

I would be careful with that. If you have a dome with a wide-angle camera, transmission is about perpendicular for all directions. If you have a flat glass, it is not. Do you want to a cube-shaped box with five cameras?

Cheers, Lars.

<image>_______________________________________________

--
Randolph Fritz • RFritz@lbl.gov
Environmental Energy Technologies Division • Lawrence Berkeley Labs

Hee.

Randolph's query reminded me that I had a search for cheap domes a while ago. This is what I found:

http://www.hammacher.com/publish/75098.asp?cm_mmc=CJ--1414665--1492714-_-Hammacher+Schlemmer

Difficult

···

On 2010-06-14 08:22:07 -0700, John Mardaljevic said:

to tell from the photo if it is optically suitable, though Fido looks quite happy. I'd be interested to hear if this is any good as a housing.

Woof woof!

-John

-----------------------------------------------
Dr. John Mardaljevic
Institute of Energy and Sustainable Development
De Montfort University
The Gateway
Leicester
LE1 9BH, UK
+44 (0) 116 257 7972
+44 (0) 116 257 7981 (fax)

--
Randolph Fritz • RFritz@lbl.gov
Environmental Energy Technologies Division • Lawrence Berkeley Labs

Hi, to complete an old thread on this and to avoid disappointment for anyone arriving from a search machine, there are acrylic domes available at Edmund Optics (not cheap but affordable):

http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=1395

as well as glass domes (not cheap but expensive):

http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=3147

Just in case someone wants to build some hemispherical capturing device or such...

Cheers, Lars.

···

On 14.06.2010 17:22, John Mardaljevic wrote:

Randolph's query reminded me that I had a search for cheap domes a while
ago. This is what I found: