HDTenEightyP/NetNews huggingface dataset:
From: sundar@fiber-one.ai.mit.edu (Sundar Narasimhan)
Newsgroups: comp.graphics
Subject: Re: Polygon (or point) within an arbitrary polygon
Date: 23 Nov 92 00:17:25 GMT
Reply-To: sundar@ai.mit.edu
Organization: MIT Artificial Intelligence Laboratory
NNTP-Posting-Host: fiber-one.ai.mit.edu

In article <1992Nov20.020732.2530@sophia.smith.edu>, orourke@sophia.smith.edu (Joseph O'Rourke) writes:
|> In article <1egv39INNj29@life.ai.mit.edu> sundar@ai.mit.edu writes:
|> >This problem [polygon in polygon] ([...]) can be solved
|> >by computing the convolution of the two polygons -- for which linear
|> >time algorithms exist in the plane. 
|> 
|> The Minkowski sum of two polygons of n and m vertices can have
|> Omega( n^2 m^2 ) vertices.  Thus if n=m, the size of the convolution
|> can be proportional to n^4.
|> 	Perhaps you are making some assumptions about the two polygons?
Yes, I was. For convex polygons A and B there is an O(n+m) algorithm 
(see Guibas et al. "Kinetic Framework for Computational Geometry"
24'th FOCS 83).

Now, for the more interesting case when A, B can be concave. Is there
a bound on the number of bounding outer edges/vertices of the Minkowski sum
(since this is all one would need to compute)? For special cases, i.e. when
the number of concavities in A + B is odd (say k), the above algorithm can be 
modified to work in O(n+m) time. A friend and I tried our hand at the
general case but couldn't get any better than O(n*m) -- and ended up
concluding that our attempts at mapping R^2xSO(1) to R^2xSO(k) had the
right sort of flavor, but was missing something fundamental that some
mathematician familiar with this could probably whiz thru in a second. 
Any further thoughts?
Newsgroups: comp.graphics.opengl
From: ramirez@mcclb0.med.nyu.edu
Subject: Off-Screen Images
Organization: NYU Medical Center, New York, NY 10016, USA
Date: Thu, 19 Nov 1992 23:12:46 GMT

Hello all,

	I know that GL is optimized to do faster image manipulations directly
onto the screen (I think).  However, is there a way to do image manipulations
with GL without displaying these images?

Thanks in advace.
ramirez@mcclb0.med.nyu.edu
From: akin@tuolumne.asd.sgi.com (Allen Akin)
Newsgroups: comp.graphics.opengl
Subject: Re: Off-Screen Images
Date: 20 Nov 1992 02:08:33 GMT
Organization: Silicon Graphics, Inc.  Mountain View, CA
NNTP-Posting-Host: tuolumne.asd.sgi.com


In article <1992Nov19.181246.1@mcclb0.med.nyu.edu>, ramirez@mcclb0.med.nyu.edu writes:
> 
> 	I know that GL is optimized to do faster image manipulations directly
> onto the screen (I think).  However, is there a way to do image manipulations
> with GL without displaying these images?

Were you asking about IRIS GL, or OpenGL?

OpenGL can be used to draw to pixmaps (under X11) or device-independent
bitmaps (under Windows NT).

Machines from Silicon Graphics often draw onscreen more quickly than they
draw offscreen, but this is a characteristic of the hardware rather than
OpenGL.  OpenGL will draw into offscreen memory at full speed on existing
machines from other vendors.

Allen
Newsgroups: comp.graphics.opengl
From: u8111031@cc.nctu.edu.tw ()
Subject: test
Organization: National Chiao Tung University
X-Newsreader: TIN [version 1.1 PL6]
Date: Mon, 23 Nov 1992 08:49:56 GMT

test

Newsgroups: comp.graphics
From: R5321GAB@vm.univie.ac.at
Subject: Re: FTP Site for 3D objects now OPEN!
Organization: University of Vienna
Date: Fri, 20 Nov 1992 21:23:11 GMT

------------------------- Original Article -------------------------

Can someone tell me how can I view those 3-d files the had an extention of
 obj?  Many Thanks.

obj is the model format from the program Wavefront which runs on Unix
workstations. I use in on the Tektronics XD8830 and the DEC 5000. It also
runs on SGI machines.

/Patrick Maun
/Hochschule fuer Angewandte Kunst
/Vienna, Austria
R5321GAB@AWIUNI11.BITNET
From: watson@maths.uwa.oz.au (David Watson)
Newsgroups: comp.graphics
Subject: Re: Point inside a triangle
Date: 17 Nov 1992 02:05:00 GMT
Organization: The University of Western Australia
NNTP-Posting-Host: madvax.maths.uwa.oz.au

watson@maths.uwa.oz.au (David Watson) writes:

>A fail-proof method is to compute the barycentric coordinates.  For a
>triangle {(x1,y1), (x2,y2), (x3,y3)} and some point (x0,y0), calculate

>b0 = (x2 - x1) * (y3 - y1) - (x3 - x1) * (y2 - y1)
>b1 = ((x2 - x0) * (y3 - y0) - (x3 - x0) * (y2 - y0)) / b0 
>b2 = ((x3 - x0) * (y1 - y0) - (x1 - x0) * (y3 - y0)) / b0
>b3 = ((x1 - x0) * (y2 - y0) - (x2 - x0) * (y1 - y0)) / b0 

>Then if b1, b2, and b3 are all > 0, (x0,y0) is strictly inside the
>triangle; if bi = 0 and the other two coordinates are positive, (x0,y0)
>lies on the edge opposite (xi,yi); if bi and bj = 0, (x0,y0) lies on
>(xk,yk); if bi < 0, (x0,y0) lies outside the edge opposite (xi,yi);
>if all three coordinates are negative, something else is wrong.  This
>method does not depend on the cyclic order of the vertices.

and if b0 == 0 => (x1 == x2 && x1 == x3 && y1 == y2 && y1 == y3)

that is, if b0 = 0 then you have an empty triangle because all
three vertices are coincident.  That is because
fabs(b0) / 2 is the area of the triangle and b1, b2, and b3,
before division by b0, are similarly related to the areas of the
subtriangles defined by (x0,y0) and each pair of the other three
points.  Notice that b1 + b2 + b3 = 1 always so if bi is > 0 the
others will compensate, and not all three can be negative.
If b1 = b2 = b3 then (x0,y0) is at the centroid (center of gravity)
of the triangle, x0 = (x1 + x2 + x3) /3, and y0 = (y1 + y2 + y3) /3.

--
Dave Watson                          Internet: watson@maths.uwa.edu.au
Department of Mathematics            
The University of Western Australia               Tel: (61 9) 380 3359
Nedlands, WA 6009  Australia.                     FAX: (61 9) 380 1028
Newsgroups: comp.graphics
From: terryr@krang.vis.citri.edu.au (Terry Robison)
Subject: How do I make a CONICAL SPLINE in POV
Summary: How do I make a CONICAL SPLINE in POV
Keywords: CONICAL SPLINE in POV
Organization: Computer Science, University of Melbourne, Australia
Date: Mon, 16 Nov 1992 04:08:31 GMT

Hello,

	How do I make a conical spline in POV raytracer.  What I
want is an ice cream cone shaped object with a thread running around it.
Is there a simple way of doing this?

		Terry
.



Newsgroups: comp.graphics
From: tld@moon.base.bellcore.com (Terry Davidson)
Subject: Re: CORAL (Corral? Chorale?) -- Anyone heard of it?
Followup-To: Corel Draw (TM)
Keywords: graphics art
Reply-To: tld@cosmos.bellcore.com
Organization: Bellcore
Date: Thu, 19 Nov 92 13:41:07 GMT

Greetings...

I've used Corel Draw, Adobe Illustrator, MicroGrafix Designer, and
Arts&Letters at my job.  I use Arts & Letters on my machine at home.

A&L, IMHO, is superior to any/all of the others; it *does not* force
one to draw in `wire frame' mode, then `preview' to see what the final
artwork is like; what you see is what you get *AS* you draw with A&L...

A&L's capability to warp text to *any* curve and into any shape, *PLUS*
`cut' a pattern to overlay on any object, *including* text, is FAR beyond
the capabilities of the others ... well, as of 6 months ago, anyway;
they'll probably duplicate A&L's functions at some point...  Example:
Get a nice brick patterned rectangle; lay the text over it; hit a couple'a
functions, and voila!  Rectangle disappears, leaving brick-patterned text.

A&L's gradient shading capabilities are more intuitive than the others.
Now, take the text manipulation and gradient shading, combine with the
`blend' function, and you get things like word spiraling out of the
background, changing colors on the way...  This particular effect really
catches attention!  BTW - this can be done with objects, also...

Anyway, 'nuff said:  I'm not affiliated (sp?) with A&L in any manner;
just an extremely satisfied customer!

-- 
*-----------------------------------------------------------------------------*
* # include disclaimer.lib   //* All standard disclaimers apply *//
* My wife let's me think my opinions are my own.  Bellcore doesn't care
* either way, and doesn't claim them anyway...
*-----------------------------------------------------------------------------*
* Terry Davidson - tld@cosmos.bellcore.com / tld@cosmos.bae.bellcore.com      *
*-----------------------------------------------------------------------------*
Newsgroups: comp.graphics
From: katkere@krusty.eecs.umich.edu (Arun Katkere)
Subject: Re: Shortest distance between two line _segments_
Reply-To: katkere@engin.umich.edu
Organization: University of Michigan EECS Dept., Ann Arbor, MI
Date: Mon, 23 Nov 1992 02:47:36 GMT

In article <1992Nov22.112142.24512@sophia.smith.edu>, orourke@sophia.smith.edu (Joseph O'Rourke) writes:
|> In article <By2z4D.How@slipknot.rain.com> robert@slipknot.rain.com.UUCP (Robert Reed) writes:
|> >In article <1992Nov21.000527.21786@zip.eecs.umich.edu> katkere@engin.umich.edu writes:
|> >|
|> >|The problem I am trying to solve is whether two swept spheres intersect.
|> >
|> >Two spheres intersect if the sum of their radii is greater than or equal to the
                                                       ^^^^^^^ lesser
|> >distance between their centers.
|> 
|> Perhaps what the original poster means by a swept sphere is the set
|> of points obtained by sweeping a sphere along a line segment, which
|> produces a cylinder with spherical endcaps.
This is exactly what I meant. Thanks for making it explicit.
I claim I was making was that two "cylinders with spherical endcaps"
intersect iff the shortest distance between the line segments along
which the spheres were swept to get those "cylinders with spherical
endcaps" was less than the sum of radii of the two spheres used in
sweeping. (Whew!)
What I wanted was how that shortest distance could be computed.
-arun
-- 
+-----------------------------------------------------------------------------+
| Arun Katkere                      |   The University of Michigan AI Lab     |
| katkere@engin.umich.edu           |   147 ATL, 1101 Beal Avenue             |
| O:(313)763-1563 | R:(313)761-9462 |   Ann Arbor, MI 48109-2110              |
+-----------------------------------------------------------------------------+
Newsgroups: comp.graphics
From: tim@cs.monash.edu.au (Tim Shimmin)
Subject: Re: Quickest way to calculate the distance between a point and a line
Organization: Computer Science, Monash University, Australia
Date: Wed, 18 Nov 1992 07:21:26 GMT

One way to find the distance between a point and a straight line can be
found in: Foley et al,"Computer Graphics: Principles and Practice" 2nd
Ed., 1990, p1100. 
It is rather simple & uses one parameter t and dot-product.

If one needs to calculate the distance quickly and is willing to accept
a possible error between 3.5%-5%, then there is an approx. equation
which does not require any squaring. This can be found in:
Foley et al,"Fundamentals of Interactive Computer Graphics" 1st Ed. 1982,
p203
and also in Pizer, S., "Numerical Computing and Mathematical Analysis",
SRA, 1975.

Tim Shimmin.
--
------------------------------------------------------------------------
          Name:        Tim Shimmin 
          Net Address: tim@bruce.cs.monash.edu.au
          Occupation:  Masters Degree Student
Newsgroups: comp.graphics
From: jdunning@phoenix.Princeton.EDU (John Alan Dunning)
Subject: Re: What are Quad Trees?
Originator: news@nimaster
Organization: Princeton University
Date: Thu, 19 Nov 1992 04:23:58 GMT

In article <martin.721555622@marsh> martin@cs.curtin.edu.au (Martin Dougiamas) writes:
>schultz@schultz.kgn.ibm.com (schultz) writes:
>>There are a bunch of papers covering the properties of quadtrees.
>>Also, octrees are the logical extension of quadtrees into 3D.
>
>I actually wrote a simple but effective solids-modeller last year using 
>linear octrees, which are a VERY space efficient way to represent volumes.
>You can also encode quadtrees linearly.  Essentially, the linear encoding
>reduces the tree to a sorted array of leaves.  There is no need for pointers.
>I found that operations like merging octrees and calculating cross-sections
>could be performed quite speedily.

Yes, octrees are extremely useful data structures.  Last year I wrote
a sort of 3D drawing program that let you sketch in 3D space using
cubes, much like you can sketch in 2D space using little squares in a
traditional bitmapped drawing program.  I used a linear octree to encode the
positions of the "voxels" (volume elements) in space.  If the user
drew eight voxels in one area so that their volume could be reprensented
by a larger octant, the program would condense them into a single,
larger octant, thus saving 7 elements in the array.  Conversely, if
the user deleted a voxel from a single large octant, the program
would decompose that octant into smaller ones until the octree
represented the new shape.  Anyway, the program handled all this
condensing and decomposing of the octree in real time.  The main speed
limitation was depthcuing the voxels on a Personal IRIS, rather than
maintaining the linear octree, even though I was using very naive algorithms
for searching the array (i.e., starting at the beginning and checking
each octant until I found the one I wanted).

John

Newsgroups: comp.graphics
From: goza@norm.JSC.NASA.GOV (Mike Goza)
Subject: Re: Point inside a triangle
Organization: IGOAL
Date: Tue, 17 Nov 1992 15:22:42 GMT

>It seems from your description that points on the boundary of the triangle
>T are not handled consistently by the ray algorithm.  Below, a is not in T
>but b is in T.
>
>			       /\	
>              		      b  c
>			     /    \
>			    +--a---+       
>
>At least this seems to be what the code that Michael Goza posted does.
>Am I right?


The above analysis is correct for the algorithm that I posted.  For that matter a point c on the
other edge would be considered outside as well.  The algorithm will make mistakes on points that
are exactly on the edge, but then how many times do computers calculate points that are EXACTLY
on the edge of a polygon.  For my purposes, the small error is fine, but your application may be
different.  I have found it to be quite satisfactory and very fast.  Everything in computers is a
compromise and the only exact thing about math is the theory.  Actual aplication is something
completely different.

Hope this clears up things,
Mike Goza
goza@cheer.jsc.nasa.gov
Newsgroups: comp.graphics
From: lee@paisly.sna.dec.com (Brian Lee)
Subject: Q: Converting a negative to a positive
Reply-To: lee@aussie.enet.dec.com
Organization: Digital CSS Sydney Australia
Date: Sun, 22 Nov 1992 23:58:41 GMT


--
Hello all you graphics experts,

I have a simple question that I'm sure all of you will be able to help
me with.

If I have a 35mm colour negative and I capture this image into say a PC
with a frame grabber then what is involved in converting this to a 
positive image ? e.g. I have grabbed a 24 plane colour neg. (i.e. no
colour map) is it as simple as doing some simple maths to create the 
positive ?

e.g. 0xffffff - negative_pixel_value = positive_pixel_value

any comments greatly appreciated

Thanks...Brian
==============================================================================
This is my signature file.

This file tells people that I don't know anything and that I don't
mean to say anything. And that Anything that sounds like I might
have said really is just a figment of the readers imagination.
=============================================================================
From: spl@pitstop.ucsd.edu (Steve Lamont)
Newsgroups: comp.graphics
Subject: Re: What's a package with well done tick (scale) marks?
Date: 18 Nov 1992 22:35:04 GMT
Organization: University of Calif., San Diego/Microscopy and Imaging Resource
NNTP-Posting-Host: pitstop.ucsd.edu

In article <2411@usna.NAVY.MIL> dfr@usna.navy.mil (PROF D. Rogers (EAS FAC)) writes:
>In article <1edpj1INN4od@network.ucsd.edu> spl@alex.ucsd.edu (Steve Lamont) writes:
>!I mean, it's pretty darn easy to write an intelligent tick mark
>!algorithm -- I've done it a couple of times.
>
>Perhaps you might like to post it. Also there is a routine
>in one of the Graphic Gems books.

The routine in Graphics Gems (Graphics Gems I, p. 61-63) by Paul
Heckbert is similar to mine -- in fact other than mine was written in
FORTRAN on an IBM 3033AP running MVS (ouch -- hit me again!) -- I'd
swear that they were the same piece of code.  Great minds and all of
that. :-) :-) :-)

							spl


-- 
Steve Lamont, SciViGuy -- (619) 534-7968 -- spl@szechuan.ucsd.edu
UCSD Microscopy and Imaging Resource/UCSD Med School/La Jolla, CA 92093-0608
"Far out, man"
            - President George Bush, heard in a stump speech on NPR
Newsgroups: comp.graphics,comp.lang.c
From: ph+@cs.cmu.edu (Paul Heckbert)
Subject: Re: Please Help Me Keep My Job!
Organization: School of Computer Science, Carnegie Mellon
Date: Fri, 20 Nov 1992 20:25:51 GMT

In article <1992Nov19.173301.3870@kpc.com> hollasch@kpc.com (Steve Hollasch) writes:
>    My manager has asked me to finish several projects by the end of this
>year, and they're really hard!  I told her I could do them, but now I don't
>know; they're pretty tricky.  I'm sure other people have done stuff like
>this, so why should I reinvent the wheel?
>net?

What a coincidence! I feel a little over my head in my job too!

In high school I used to like to shoot small animals with my bb-gun,
and my dad's friend down the street ... well ... he liked me I guess and he
got me a job here at the Pentagon right after I graduated!!  Mr. Quayle
has always been real nice to me. It's really cool here where I work
I've got a whole CM-5 to myself and they give me exciting things to
work on and learn about.  They gave me a bunch of technical magazines
and told me to try to figure out how to use neural networks to target
IBCM's.  These neural networks sound really cool and all but I can't
figure out the math!!!!!  Yuck!

But your job sounds better for me.  Do you work with fractals
and virtual reality and awesome stuff like that??
I know C pretty okay so maybe I could do your tasks and you
could do mine.  We could exchange work with email!!

-Bob "BB" Spudhead

		    bb@cm5.nukem.pentagon.mil

		    Projectile Trajectory Division
		    Strategic Defense Initiative
		    DoD
Newsgroups: comp.graphics
From: Ron Beloin <R.Beloin@cornell.edu>
Subject: looking for info-color bitmap filters
X-Xxmessage-Id: <A72D60E07E020E56@theq.cit.cornell.edu>
X-Xxdate: Mon, 16 Nov 92 14: 29:52 GMT
Nntp-Posting-User: rmb1@cornell.edu
Organization: Boyce Thompson Inst.
X-Useragent: Nuntius v1.1.1d12
Date: Mon, 16 Nov 1992 19:25:55 GMT


I've been searching for books/algorithms/code/whathaveyou for examples of
filtering color pixel images for special effects. I've checked the FAQ
and the local library and bookstore, but so far not much info. There were
some common techniques like blurring and rotating. I'm looking for more
interesting things that can be done to an image. The graphics gems series
seems to have a bit of this stuff, but I was hoping to find something like
``101 fun filters for images, with C code (disk included).'' :-)

TIA,
Ron Beloin, Boyce Thompson Inst., Ithaca, NY
R.Beloin@cornell.edu
Organization: Arizona State University
Date: Monday, 23 Nov 1992 13:58:36 MST
From: <AGDAV@ASUACAD.BITNET>
Newsgroups: comp.graphics
Subject: GIF viewer for IRIS 3030

     Can anyone tell me where I might find a GIF or JPEG viewer
     for the IRIS 3000 series ?

                                      - Thanx
                           Dave   agdav@acvax.inre.asu.edu
Newsgroups: comp.graphics
From: kenneth@dekalb.dc.peachnet.edu (Kenneth Palmertree)
Subject: Re: MPEGXING QUESTION..HELP!
Organization: DeKalb College
X-Newsreader: TIN [version 1.1 PL7]
Distribution: usa
Date: Sat, 21 Nov 1992 17:14:36 GMT

Does Mpegxing support the ATI Graphics Ultra Video card?

-- 
Real Name     : Kenneth Palmertree
Internet      : kenneth@dekalb.dc.peachnet.edu
Phone Number  : (912)-746-3034
Computer Type : Laser 486/33 Tower
From: sundar@fiber-one.ai.mit.edu (Sundar Narasimhan)
Newsgroups: comp.graphics
Subject: Re: Polygon (or point) within an arbitrary polygon
Date: 19 Nov 92 20:57:13 GMT
Reply-To: sundar@ai.mit.edu
Organization: MIT Artificial Intelligence Laboratory
NNTP-Posting-Host: fiber-one.ai.mit.edu

In article <HINKER.92Nov19081251@cocker.acl.lanl.gov>, hinker@acl.lanl.gov (Paul J. Hinker) writes:
|>    I have Polygon1 and Polygon2 described by their respective vertice
|> lists and bounding boxes and I would like to find out whether or not
|> Polygon1 *contains* Polygon2.  Nothing else is known about either
|> polygon.
This problem (like the polygon intersection problem) can be solved
by computing the convolution of the two polygons -- for which linear
time algorithms exist in the plane. 

Let's say you have polygon A, B. First let's consider determining
if A intersects B. To do this imagine shrinking B to a point, and growing A
by the similar amount. Now if the point representing B is in the 
grown polygon GO_B(A) (read that as "grown obstacle A relative to B),
then they must intersect. What do I mean by "growing A by a similar amount"?
I mean that A is replaced by the convolution of the two polygons A and
-B (negated copy of B where every vertex V_i in B has been replaced by -V_i).
Thus queries about intersection can be reduced to the point in polygon
problem. 

Your containment problem is essentially the same. If you consider
the complement of A, your problem is deciding if B intersects complement of
A. Note that generating complements is extremely easy (just switch
the signs of edge-normal information - or change ccw polygons to cw ones).
Newsgroups: comp.graphics
From: cplai@csie.nctu.edu.tw ()
Subject: Image processing, sharpen, calibrate, dither, contrast.....
Organization: Dep. Computer Science & Engin. of Chiao Tung Univ., Taiwan, ROC
Date: Wed, 18 Nov 1992 13:51:50 GMT


Hi:
    I am doing a image processing project right now, I have to manipulate some
functions to a scanned picture. like sharpen, calibrate, dither, contrast.....,
Could someone give me some directions how to find the infos?
    I need to know the theory and how to implement it, of course, any source
codes will be appreciated.

   Please reply to:
   cplai@ccsun5.csie.nctu.edu.tw

   Thanks.


scott
From: dfr@usna.navy.mil (PROF D. Rogers (EAS FAC))
Newsgroups: comp.graphics
Subject: Re: "Scientific American Frountiers" rips off SIGGRAPH
Date: 16 Nov 92 17:20:04 GMT
Organization: U. S. Naval Academy

In article <1992Nov16.141305.2999@ra.msstate.edu> mrr1@Ra.MsState.Edu writes:
!In article 2388@usna.NAVY.MIL, dfr@usna.navy.mil (PROF D. Rogers (EAS FAC)) writes:
!! In article <1992Nov13.193353.2158@megatek.com! tomw@stephanie.megatek.com (Tom Wright) writes:
!! !Wednesday night on PBS, "Scientific American Frountiers" presented during
!! !their hour long show a roughly 5 minute segment on SIGGRAPH '92. They showed
!! !the exhibit hall, featured "The Cave", and showed examples of scientific
!! !visualization. Yet they NEVER MANAGED TO SAY THE WORD "SIGGRAPH"! And just 
!! !in case you saw the clip and would give your right arm to attend the next 
!! !conference, they never said the next one would be in Anaheim or that it 
!! !would be next summer.
!! !
!
!I would much rather they give the topic partial attention than none at all.
!
!Mark

No, I disagree. What was done is intellectually dishonest. I'd rather
they did nothing than do that.

Dave Rogers

Newsgroups: comp.graphics
From: banister@rintintin.Colorado.EDU (Trevor Banister)
Subject: SVGA animation maker?
Summary: Wanted: SVGA animation maker.
Keywords: animation FLI animation
Organization: University of Colorado, Boulder
Date: Mon, 16 Nov 1992 00:36:53 GMT

Does anyone know of an SVGA animation maker?
Any format is allright. FLI, GL, DL, etc.
I'm interested in 640x480x256 or greater.

Email to banister@rintintin.colorado.edu.

or post here.

Thanks.

Trevor Banister

Xref: sparky comp.graphics:12029 comp.graphics.visualization:1783