Radiance Digest Volume 1, Number 4

Dear Radiance User,

Here is another culling of mail regarding Radiance.  There are many new
users since the last mailing, and if you are one of them I would like to
send you my welcome.  Also, if you would like back issues of this digest,
just send me some mail.  (No one has asked for any yet -- should this be
telling me something?)  Topics included in this digest are the following:

	GEOM	Geometric Primitives in Radiance
	ATMOS	Simulating Atmospheric Effects
	LARGE	Large Radiance Models
	PORT	Portability Issues (on the long side)
	PINTERP	Uses for the Pinterp Program

GEOM	Geometric Primitives in Radiance

Date: Sat, 8 Jun 91 17:24:43 NZT
From: pdbourke%ccu1.aukuni.ac.nz@Csa2.lbl.gov
Subject: Polygon primitive
To: GJWard@Csa2.lbl.gov

Regarding my raving earlier about the ordering of polygons for the direction
of facet normal...how about a special polygon primitive which is defined
as double sided, it is really two polygons with the same vertices but one
ordered clockwise and the other anticlockwise. It seems better to make this
a primitive that the renderer "knows" about than to have the data files
include both polygons. Does Radiance handle coincident polygons like that
descibed above?
Also I am fustrated by renderers which don't know about lines and therefore
force me to turn lines into cylinders. It would seem nicer for the renderer
to turn them into cylinders of radius = 1 pixel, ie: normally the modelling
or translator software does not know the pixel size (image space not world) 

	Paul D Bourke

Date: Mon, 10 Jun 91 08:57:54 +0200
From: greg (Greg Ward)
To: pdbourke%ccu1.aukuni.ac.nz@Csa2.lbl.gov
Subject: Re:  Polygon primitive

Hi Paul,

As I said in an earlier mail, Radiance ignores polygon "sidedness" for all
material types except dielectric.  Thus, most polygons in fact act as though
they are two-sided during rendering.  Dielectric objects must be modeled as
solids, since light refraction happens on entry and on exit, and a two-sided
polygon would be equivalent to an infinitely thin volume, which should be
modeled instead by the material "glass" that is designed for this purpose
and that ignores surface orientation.

The hack used by most scanline renderers of culling back-facing polygons
does not really help that much in a ray tracer so I felt that all faces
should be treated as two-sided in Radiance.  This makes the modelers job
a lot easier (whether it be a modeler programmer like youself or some poor
fool like me using a text editor).

To answer your question, "does Radiance handle coincident surfaces?" I would
have to say no.  There is a well-known problem in ray tracing which is 
avoiding a reintersection with a surface upon reflection or refraction.
For polygons, it is an easy decision not to test the intersected surface
again for intersection, but spheres and other curved surfaces can have
multiple intersection and the decision is not so straightforward.  The
nicest way to avoid this problem is to insist that the first intersection
be some minimum distance from the starting point, which precludes the
possibility of properly handling coincident surfaces as well.  I could
discuss this topic in more detail, but I see my letter running off the
top of the screen and sense that I should move on.

Drawing lines does not make sense for a physically-based rendering program
because lines in fact do not exist.  I suppose true two-dimensional surfaces
don't exist either, but for the purpose of light interaction they are a
fair approximation of the real world.  Physics aside, it is not easy in
a ray-tracer to decide which pixels to paint with a line because the
rays go into the scene from the pixels and may not even be aware when
they pass close to a line.  Line drawing works much better the other
way where you start with the world coordinates of the line and draw
a nice pixel-width object on the image.  Believe it or not, Radiance
sometimes does not even know what the pixel size is because it is
frequently used in a luminance mode where it is not generating an image
but is being used instead to calculate light levels.  Also, since lines
are non-physical, it would not be possible to shade them properly and
they would wind up as these anomolous glowing objects in an otherwise
natural-looking scene.

For the purpose of rendering with a ray-tracer, it really makes the
most sense to convert the lines into cylinders as you do and
give them a radius that makes the most sense of the size of the
object the lines are meant to represent, ie. grass or sticks or
whatever.  The lines may show up as thicker up close and thinner
(or dissappearing) at a distance, but this is the nature of physical
reality.  Setting the line width proplerly usually means leaving it
to the user.


Date: Thu, 1 Aug 91 8:43:19 NZT
From: pdbourke%ccu1.aukuni.ac.nz@Csa2.lbl.gov
Subject: A few questions
To: GJWard@Csa2.lbl.gov

I have been using radiance a bit now although generally in a simple minded
way, I do have a question on which you may have some suggestions.

What is the "nicest way" to include parameters in a scene description. For 
example, define some constants which are used thoughout the scene description.
This would allow the user to change the constants to meet his/her needs.
A real example, I would like to define a constant called RADIUS say, this
would be used thoughout the geometry description of cylinders and spheres.

	Paul D Bourke

From greg Fri Aug  2 08:38:51 1991
Date: Fri, 2 Aug 91 08:38:50 +0200
From: greg (Greg Ward)
To: pdbourke%ccu1.aukuni.ac.nz@Csa2.lbl.gov
Subject: Re:  A few questions

Hi Paul,

I have considered from time to time adding variables to the scene description
but never did it.  I guess I wanted to keep the job of parsing the scene
files as simple as possible for other programs/programmers who might want
to use the information.

The first method that occurs to me for adding variables to the input file is
with the C language preprocessor, /usr/lib/cpp, or better yet the macro
processor m4.  This will allow you to define variables as well as (macro)
functions with arguments.  I have not tried this myself, but I see no reason
why it wouldn't work.


Date: Sat, 3 Aug 91 14:31:53 NZT
From: pdbourke%ccu1.aukuni.ac.nz@Lbl.Bitnet
Subject: Radiance (of course)
To: greg%lesosun1.epfl.ch@Lbl.Bitnet
Thanks for the reply, I didn't think that parameters were possible in the
Radiance scene description but thought I would check in case there were
some as yet undocumented features.
You may have noticed a new version of Vision3D in the Mac FTP folder. If not
then you may want to change the file privileges.
Has anyone else to your knowledge written a translator from Super3D (another
Mac modeller, not all that powerful but widely used, it is to 3d modelling
what Lotus is to speadsheets - the product to which others are compared). I
have worked on one over the last week for a project here, before I develop
it much further I would like to make sure there is not already something
out there.
I'll send you a GIF sometime soon of some 3D L-System plants I've been
working on recently. They look quite good I think, the application that
allows the user to specify the production rules, etc, exports to Radiance.

	Paul D Bourke
Date: Mon, 5 Aug 91 10:00:04 +0200
From: greg (Greg Ward)
To: pdbourke%ccu1.aukuni.ac.nz@Lbl.Bitnet
Subject: Re:  Radiance (of course)

Hi Paul,

Thanks for the new version of Vision3D.  I did noticed it and renamed
the files, getting rid of the old one and updating the README file.
I have since made the README file in that directory writable so you
can modify it if you like.

I have had a student working (for some time) on translating the Renderman
output of Sculp3D into Radiance format, but I don't know off hand of anyone
who has worked with Super3D files.

You can drop GIF (Targa, PICT, Sun rasterfile, Radiance pictures) off
in the pub/xfer directory on hobbes with anonymous ftp.  Which reminds
me, I need to write some new image format translators...  My prediction
for computer science is that in two years the hardware industry will
abandon the ASCII standard and the QWERTY keyboard and the few bitter
programmers left will spend all their time hacking on new viruses.


ATMOS	Simulating Atmospheric Effects

To: greg@hobbes.lbl.gov
Subject: Atmospheric effects
From: Jerrell Ballard  
Date: Thu, 13 Jun 91 11:31:34 EDT

  Hello Greg,

  Are you aware of any RADIANCE functions that *roughly* approximate
  atmospheric effects ?  I have been generating some landscape scenes,
  and then post-processing to add the atmospheric effects.  It would
  handy to be able to add atmospherics at time of rendering. 

  Jerrell Ballard
  Geographical Information Systems Team
  Waterways Experiment Station
  United States Army Corp Engineers

From greg Fri Jun 14 08:56:22 1991
Date: Fri, 14 Jun 91 08:56:18 +0200
From: greg (Greg Ward)
Message-Id: <9106140656.AA06417@lesosun1.epfl.ch>
To: ballard@mc1.wes.army.mil
Subject: Re:  Atmospheric effects
Status: RO

Hi Jerrell,

If by atmospheric effects you are referring to scattering, absorption, etc.,
the answer is no, Radiance does not support it.  You can, however, model
high clouds and other patterns in the sky directly in Radiance.  If this
is what you are after, I can give you some hints and examples in another
letter.  For now, I'll assume that what you want is the former.

The best post-process to get a rough approximation to scattering (and/or
absorption) would use the -z option of rpict to produce a file of pixel
distances then use this information to modify the colors in the final
picture.  This would be done most efficiently by a special purpose program,
but you can do it also with the existing tools pvalue and pcomb.

By way of example, let's say you want to imitate haze that fades to white
as an exponential function of distance.  You would first render an ordinary
image with rpict, using the -z option to produce a distance file, like so:

% rpict -x 512 -y 480 -z scene.z scene.oct > scene.pic

Then you would use pvalue together with pcomb to apply the desired function
to the pixels based on their distance.  Pvalue is necessary to convert the
machine floating point numbers in the z-file into a Radiance picture 
because pcomb only works on this format.

% pvalue -r -b -h -df -x 512 -y 480 scene.z | \
	pcomb -e 'ro=f(ri(2));go=f(gi(2));bo=f(bi(2))' \
		-e 'f(p)=c*p+1-c;c=exp(-gi(1)/udist)' \
		-e 'udist=50.0' - scene.pic > scene.fade.pic

Note that it is necessary to repeat the image size to pvalue so it knows
what to do with scene.z.  The unit fade-out distance "udist" can be
changed from 50.0 to whatever you like to provide the desired fade-out.

If you tell me what kind of effects you desire (perhaps after some
experimentation), I may even write a program to do it more efficiently
for you (still as a post-process, though).  I never did much with
atmospherics because most of my scenes are indoors, and I prefer to
create accurate physical simulations rather than quick hacks.
However, atmospherics is one thing I don't expect to be able to treat
correctly within Radiance in the near future, so a hack is the best
I can do.


LARGE	Large Radiance Models

Date: Mon, 1 Jul 91 12:01:59 NZT
From: arch2@ccu1.aukuni.ac.nz
Subject: Large Radiance Models
To: greg@hobbes.lbl.gov


I have been trying to get Radiance to work with models containing
about 10,000 spheres, stored in a text file of about 1M, and keep
getting the "out of octree" space message from oconv.

In your first Radiance digest you suggest ways of increasing the
size of models oconv can handle. None of these seem to do the

I have tried these values:
    MAXOBJBLK in object.h is 65535
    MAXOBLK   in octree.h is 524287
    OSTSIZ    in objset.c is 1047821 (It is prime)

I also changed OBJECT to a long.

oconv dies with this message:
    oconv: system - out of octree space: Not enough space

According to ps -l oconv uses up to about 2,500K of memory. (The machine has
64M and I am allowed a maximum of 10M). The exit code is 2, if it helps.  

Also, what does the '-n' parameter do. On my "smaller" models '-n 7' or
similar stopped the error message.

Thanks in advance,
Russell (for Paul Bourke)

Date: Mon, 8 Jul 91 11:22:47 +0200
From: greg (Greg Ward)
To: arch2@ccu1.aukuni.ac.nz
Subject: Re:  Large Radiance Models

Hi Russell (and Paul?),

I think your problems with oconv must be due to memory limitations, since
it is a malloc failure that is stopping the process.  If you can't find
any other system variables or administrative things that our limiting
your process size (Cray's operating system places limits on interactive
sessions, for example), then you might try replacing the COMPAT=malloc.o
to COMPAT=bmalloc.o in ray/src/{rt,ot}/Makefile and recompiling.  This
will use the system version of malloc rather than my home-grown routines.
Sometimes people do some pretty strange things with memory allocation.

The -n parameter to oconv makes the octree place more surfaces into the
octree voxels.  It is a good idea to increase this number for very complex
scenes if memory is a problem.  You can jack it up to around 16 with little
degradation in rendering time -- at least for spheres.


Date: Tue, 16 Jul 91 17:46:33 NZT
From: arch2@ccu1.aukuni.ac.nz
Subject: Large Radiance Models
To: greg@lesosun1.epfl.ch

I am still having "fun" with my large models.

Would splitting the .rad file into smaller pieces and using
oconv to merge them together help?

Some of the programs I ran today wanted 64M of memory -- they
were run in batch mode where processes are allowed that much memory.



Date: Tue, 16 Jul 91 17:47:45 NZT
From: arch2@ccu1.aukuni.ac.nz
To: greg@lesosun1.epfl.ch

These are the statistics printed out (from the routine PrintMemStats):

oconv-l: system - out of octree space: Not enough space
Memory statistics:
	bmalloc: 66437172 bytes allocated
	bmalloc: 3936 bytes freed
	bmalloc: 28696 bytes scrounged
	malloc: 11931552 bytes allocated
	malloc: 5796830 bytes wasted (48.6%)
	malloc: 6006992 bytes freed
	238 * 512
	395 * 256
	720 * 128
	257 * 64
	12 * 32
	53 * 16
	2 * 8
	 346248 total bytes in free list

Date: Tue, 16 Jul 91 10:05:02 +0200
From: greg (Greg Ward)
To: arch2@ccu1.aukuni.ac.nz
Subject: Re:  Large Radiance Models

Hi Russell,

Thank you for the details on the oconv errors.  Oconv should be able to
handle 10,000 non-intersecting spheres quite easily.  Your spheres must
be intersecting an awful lot or you are using more spheres than you claim
to be running over 64 Mbytes of memory!

Things you can do about it:

1) Change your scene generator so as to avoid generating so many
intersecting spheres.

2) Increase the -n parameter of oconv to 120.

3) Decrease the -r parameter of oconv by half or so.  (This will
cause a set overflow error if you decrease it too much.)

4) Try generating the octree in stages (as you suggested) by giving
oconv progressively more spheres to add to the scene.  You may have
to use the -b option on the initial run of oconv to tell it what you
expect the eventual scene boundaries to be.

5) Use the Radiance instance type to duplicate sections of your scene
rather than enumerating everything.  This is the best method to achieve
geometric complexity without using up all available memory.  You simply
create a fraction of the scene you want, then instantiate it throughout
the environment.  Using heirarchical instancing, it is easy to create
models with many millions of surfaces.

Let me know if I can be of any more help.

PORT	Portability Issues

Date: Tue, 16 Jul 91 22:27:29 CDT
From: stephens@minnie.wes.army.mil (Mike Stephens)
To: GJWard@Csa2.lbl.gov
Subject: radiance
this is mike stephens at waterways experiment station (wes) in vicksburg, miss.
i just got the 5th release of your program radiance 1.4 and plan to use it
for several projects we have going on at the scientific visualization center

i have tried to compile it on our sgi (4D) boxes and have run into some
problems. i was wondering what sgi machines you have successfully
installed radiance on?

i get errors in the 'malloc.c' routine (v_pageshift not defined)
also things in tty.c get 'twisted' somehow.

we are running irix ver 3.3.2 on our sgi's.

any help on this would be greatly


Date: Wed, 17 Jul 91 08:57:27 +0200
From: greg (Greg Ward)
To: stephens@minnie.wes.army.mil
Subject: Re:  radiance

Hi Mike,

You need to change the COMPAT=malloc.o to COMPAT=bmalloc.o in the
Makefiles in the src/rt and src/ot directories.  The memory stuff
has not been very well standardized under System V, so some of the
definitions in my malloc.c cause trouble for some implementations.
The routines in tty.c are really written for BSD derivatives, and
don't work for any System V Unix's, but this module is only used
by the AED 512 driver, which you probably don't need.  I guess I
made an error in my makeall script and included this driver when
I shouldn't have.  Anyway, it just won't be made properly --
everything else should work fine.  If you want, you can change
the line in makeall under the Silicon Graphics IRIS choice from
special="aed" to special=

I have never tried to compile 1.4 on an IRIS, just 1.3.  I no longer
have easy access to an IRIS workstation.  (Actually, I have never
had easy access to anything except a Sun 3/60.)

Hope this helps!

From: stephens@slowhand.wes.army.mil
To: GJWard@Csa2.lbl.gov
Subject: sgi's and radiance


many thanks for your quick response!
the malloc problem could have been solved by yours truly if
i had bothered to CAREFULLY read the comments in malloc.c.
oh, well....

instead of the bmalloc=>malloc solution for the sgi anyway
i changed malloc.c so that getpagesize was called as a system
routine (which it is on the sgi irix 3.3.2) and also added
an include because as it wass it couldn't find the type 'daddr_t'
which is in  in irix 3.3.2.

did this last night after i wrote to you and viola the main
critters got made!! aed still didn't but at least i had the
majority of the goodies to play with.

went in first thing today (7/17) and drew a pretty daffodil!!!
your code is pretty slick...thanks for your efforts...
atta boy... and all that stuff.

take care
mike (stephens@slowhand.wes.army.mil)

Date: Wed, 17 Jul 1991 13:52 +0200
From: "Sigge Ruschkowski email:f87-sir@nada.kth.se or kjr@ekab1.ericsson.se"
Subject: Radiance for the Mac
To: greg@hobbes.lbl.gov

	Hi Greg,

	I read in RTNEWS that there is a version of Radiance
	for the Mac. What kind of Macs does Radiance run on?


Date: Wed, 17 Jul 91 17:28:48 +0200
From: greg (Greg Ward)
To: KJR@kkeka1.ericsson.se
Subject: Re:  Radiance for the Mac

Hi Sigge,

Radiance runs under A/UX (Apple's UNIX) on the Mac II family.  Since
most folks use the ordinary Mac OS, this doesn't do much good.  But,
if you're interested in A/UX for the MacIntosh, it's not all that
expensive and Radiance will run on it.  I've been using a Mac IIfx
myself successfully to do animations using Radiance.

A/UX costs around $500 in the US and X11 software is another $200 or so.
The main drawback is that it requires 80+ Mbytes of disk space and X11
doesn't run well unless you have at least 8 Mbytes of RAM.  Also,
installation is difficult unless you buy it already installed on an
Apple external drive (very expensive).  CD-ROM is the next best
installation method.  You don't want the floppy disk product!


Date: Thu, 18 Jul 1991 08:02 +0200
From: "Sigge Ruschkowski email:f87-sir@nada.kth.se or kjr@ekab1.ericsson.se"
Subject: Re: Radiance for the Mac
To: greg@lesosun1.epfl.ch

    Hi Greg,

    thank you for the answer!

    As I am using my MacII/8/170 just for private things and 
    am just a poor student, I can't afford to by AUX and a
    80MB hard drive. We will soon have AUX on some of the 
    Macs at school and I will get your ray-tracer and try
    it out.

    Have a nice life,

To: greg@hobbes.lbl.gov
Subject: Radiance1R4.tar.Z
Date: Thu, 18 Jul 91 11:42:39 EDT
From: Scott Hankin 

Howdy -

    I've been trying to work with your latest release, and I appear to be
missing some files.  When I try to build the cubspace model, make tells me it
doesn't know how to make "proof" which the model depends upon.  When I try to
run rview on anything, it fails because it can't open rayinit.cal.  I can't find
rayinit.cal in the tree, I deleted the distribution after expanding it, and I am
reluctant to ftp it again to see if it was indeed in the distribution, but
deleted by one of the many makeall clean's I did while getting things going.

    Can you help me out with these files?  I'd really appreciate it.  Thanks.

- Scott

Scott Hankin  (hankin@osf.org)
Open Software Foundation

Date: Fri, 19 Jul 91 08:54:05 +0200
From: greg (Greg Ward)
To: hankin@osf.org
Subject: Re:  Radiance1R4.tar.Z

Dear Scott,

Sure enough, the critical file "proof" was missing from the distribution.
An over-zealous cleanup job on my part, I'm afraid.  I've added it back
in again -- thanks for bringing it to my attention.  To save you from
ftp'ing it again (though it's small), I'll send you the file in the next

The rayinit.cal file (and other essential library files) come in the ray/lib
directory of the distribution.  They are not deleted by any cleanup procedure
I wrote, but you may not have remembered to set the RAYPATH environment
variable to tell the programs where to find this directory.  The makeall
script is supposed to do this automatically, but it only works if you
tell it to go ahead and install the library in the location you select.
You can always set the RAYPATH variable manually with a line in your
.login file like so:

	setenv RAYPATH .:/installpath/ray/lib

Where "installpath" is replaced with the place you installed the distribution.

Hope this helps!

To: "(Greg Ward)" 
Subject: Re: Radiance1R4.tar.Z 
Date: Fri, 19 Jul 91 09:47:43 EDT
From: Scott Hankin 

    It does indeed.  Thanks for the info - things are up and running great even
as we speak.  It seems that in a moment of insanity (and a temporary shortage of
disk space) I removed the ray/lib subtree - for some reason I had decided it was
generated during the build process.  I was obviously wrong.

    Thanks for the help, the software, the work it involved - thanks for
everything.  I never cease to be amazed at the effort folks like you will put
into things they make available to the public.  You are one of the heroes of
learning.  I know I will get a great deal out of using and examining Radiance. 
Keep up the terrific work!

- Scott

Scott Hankin  (hankin@osf.org)
Open Software Foundation

The following message is not specifically about Radiance, but it does
get around a bug in the 1.4 release of x11image so take note.  By the
way, both x11image (now called just plain old "ximage") and xshowtrace
have been fixed for the next release.

Date: Sat, 20 Jul 91 12:23:12 PDT
From: raja@robotics.berkeley.edu (Raja R. Kadiyala)
To: robotics-users@robotics.berkeley.edu
Subject: xdvi and openwindows

Many have noticed that some programs such as xdvi and xfig do not work
properly under openwindows -- they fail to accept input in the window.

The fix is to tell the window manager to explicitely get input from the window
this is done by putting the following lines in your
.Xresourses/.Xdefaults/.Xdef (or wherever your applications resources are

xfig.Input: true
xdvi.Input: true


Date: Wed, 7 Aug 91 20:09:43 EDT
From: chen@eleceng.ee.queensu.ca (Junan Chen)
To: greg@hobbes.lbl.gov
Subject: Radiance
Status: RO

Hi, Greg:

Thanking you for your mail of July 31.  I tried to grab Radiance at midnight,
and successfully got everything I need.

After I installed the Radiance, I found *rview* didn't get compiled.  I also
checked the *devtable.c*, and the default_driver is x11_init(), though I 
replied "no x10 support" during the installation.  I modified default_driver
of devtable.c to *sun*, but *make  rview* still doesn't work properly.

The other thing is how to specify the focal length with the command *rpict*.
I checked the reference manual and relevant manual pages, but couldn't find
any direct way to do that. 

Could you please give me some hint to my questions.

BTW, we use a sparc-2 station with a 24-bit graphics adaptor which is compatible
with CG8 and can be set up as 8-bit CG4 as well.  Most of the time we use it as
a 8-bit CG4 workstation.

I really appreciate your help.

Junan Chen
Date: Thu, 8 Aug 91 09:46:06 +0200
From: greg (Greg Ward)
To: chen@eleceng.ee.queensu.ca
Subject: Re:  Radiance

Hi Junan,

I have had this asked of me before, so I decided to make a little readme
file explaining what to do if you don't have X11 support.  I've attached
it to the end of this letter.  (When you answered "no" to X10 support,
the script still assumed you had X11 support -- which is very different!)

There is no adjustment for focal length, since the renderers do not have
depth of field in their simple pinhole camera model.  If you want this,
you will have to add it yourself.  [But see PINTERP topic below -G]


This Radiance distribution assumes that you have X11 support
(ie.  a /usr/include/X11 directory and /usr/lib/libX11.a library).
If this is not the case, you will have to make a couple of changes
to the files in the src/rt directory to make "rview" compile properly.  
If you are a thorough person, you can also make changes to the Makefile's
in the src/util and src/px directory to avoid some other spurious but
unimportant errors.

The following diffs should be applied to Makefile and devtable.c in the
src/rt subdirectory:

============= rt/Makefile =============
< DOBJS = devtable.o devcomm.o editline.o x11.o x11twind.o \
> DOBJS = devtable.o devcomm.o \
< DSRC = devtable.c devcomm.c editline.c x11.c x11twind.c \
> DSRC = devtable.c devcomm.c \
< DLIBS = -lX11
> DLIBS = 

============= rt/devtable.c =============
< char  dev_default[] = "x11";
> char  dev_default[] = "sun";
< extern struct driver  *x11_init();
< 	{"x11", "X11 color or greyscale display", x11_init},
> 	{"x11", "X11 color or greyscale display", comm_init},

These changes may be applied to the Makefile's in the src/util and
src/px subdirectories for cleaner compilation:

=============== px/Makefile =============
< ra_t8 ra_bn ra_t16 pcomb pinterp ximage xshowtrace pflip
> ra_t8 ra_bn ra_t16 pcomb pinterp xshowtrace pflip

=============== util/Makefile ============
< PROGS = makedist swaprasheader findglare xglaresrc glarendx
> PROGS = makedist swaprasheader findglare glarendx

PINTERP	Uses for the Pinterp Program

From: Frank Bennett 
Subject: Radiance
To: greg@hobbes.lbl.gov
Date: Tue, 20 Aug 91 9:46:15 MDT

	I just picked up Radiance. Look's interesting. I found the following

	obj/cabin/tree.rad  - landscape wants to instanciate tree.oct
	I have done alot yet, did go back & pick up some .pic files
	& pub/objects/gjward.tar.Z

	I have not been able to assertain (from Raytracing News or your
	package) whether you generate "lit" polygons with soft shadows,
	which you can then walk through. The advantage of a Radiosity
	system is you only need to recompute the sceen if the lights or
	objects are moved, but not for camera moves.

good work,

Frank Bennett - Hewlett Packard 
P.S. a plug: Our new Snake CPU love to raytrace, the aquarium from:


	Spark2     52 hours
	Cray YMP   18 hours
	HP9000/720 17.5 hours
	HP9000/750 13 hours

Date: Wed, 21 Aug 91 08:26:06 +0200
From: greg (Greg Ward)
To: fwb@hpfcfwb.fc.hp.com
Subject: Re:  Radiance

Hello Frank,

It sounds like you need to set the environment variable RAYPATH to
the location of the library directory because it's not in the default
location /usr/local/lib/ray.  The README file should explain it, but
basically you need a line in your .login like:

	setenv RAYPATH .:/my/radiance/path/lib

Then the problems you mentioned should go away.

As for soft shadows, the default options of rpict produce sharp shadows,
but you can set the following if you want soft shadows:

	-sp 1 -dj .5

The -sp 1 value turns off image plane sampling, so the renderings will
take substantially longer.  Also, if you don't do any anti-aliasing by
running the result through pfilt and reducing the resolution, the shadows
will appear noisy.

I am aware that soft shadows and walk-through animations are big advantages
of radiosity methods, but then you're stuck with simple polygonal scenes
and diffuse surfaces, so it's a tradeoff.  I have implemented a z-buffer
interpolation program, pinterp, for generating walk-through animations that
makes ray tracing a reasonable way to go, actually.  It would be nice to
store all that shadow information somehow in the scene, but the memory
requirements are daunting.  We're running these programs on small machines,
too you know.

Thanks for your input.

Date: Wed, 14 Aug 91 17:24:34 -0400
From: hr3@prism.gatech.edu (RUSHMEIER,HOLLY E)
To: greg@lesosun1.epfl.ch

For our computer vision project, we are using Radiance to model a
finite size pinhole by making lots of images from different points in
the pinhole and then adding them up, accounting for the shifts in pixel
location. Apart from writing new code, is this the only way to do this?


Date: Thu, 15 Aug 91 09:41:30 +0200
From: greg (Greg Ward)
To: hr3@prism.gatech.edu
Subject: looking at the world through a pinhole

Hi Holly,

Regrettably, I can't think of any more direct way to do pinhole sampling
than what you're doing already.  However, there is a way you can do it
a little faster, I think.  Generate an image from the center using rpict
with the -z option to generate a z-file.  Then, use pinterp with the
following options to produce images at different points like so:

	% rpict [opts] [view] -x xres -y yres -z scene.z scene.oct > scene.pic
	% pinterp -vf scene.pic -vp x1 y1 z1 -vs h1 -vl v1 -x xres -y yres \
		-ff -r "[opts] scene.oct" scene.pic scene.z > scene1.pic

Pinterp just moves the pixels around according to the new viewpoint using
a z-buffer approach and calling on rtrace (in this case) to compute
pixels it cannot find.  The only problem with this technique is that it
does not correctly follow specular reflections in the new image, so if
you are trying to see depth of field in a reflection you need to wait
for rpict.

Also, you can use the view shift and lift parameters to do the pixel
shifting for you.  You just have to compute the appropriate values based
on the distance to your pinhole's image plane.  I would work out the
formulas for you, but I'm sure I'd make some dumb error.

Finally, I would recommend using pcomb to add the images up if you aren't
using it already.  You can give a scalefactor of 1/N for each image
and when you pass it through pfilt later you should get the correct
radiance values.

Let me know if I can be of any help, and thanks very much for sending
the report and the announcement.


Back to Top of Digest Volume 1, Number 4
Return to RADIANCE Home Page
Return to RADIANCE Digests Overview

All trademarks and product names mentioned herein are the property of their registered owners.
All written material is the property of its respective contributor.
Neither the contributors nor their employers are responsible for consequences arising from any use or misuse of this information.
We make no guarantee that any of this information is correct.