Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1998
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1998

[Date Index] [Thread Index] [Author Index]

Search the Archive

LightSources

  • To: mathgroup at smc.vnet.net
  • Subject: [mg14440] LightSources
  • From: Maarten.vanderBurgt at icos.be
  • Date: Wed, 21 Oct 1998 03:32:36 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

In the MathGroup archives I found two messages with some questions
regarding light sources. I attach them below. I did not find any
answers or responses to them. Currently I have the same questions as in
these two messages. I did read section 2.9.12 in the book and related
help items. But this does
 not answer all these questions.
Is there anyone who knows more about this or who can point me to the
right sources?

thanks

Maarten van der Burgt

Icos Vision Systems
Leuven
Belgium


******************************************************* From: Alex
Tabarrok <00attabarrok at bsu.edu.bsu.edu> To: mathgroup at smc.vnet.net
Subject: [mg14440] [mg7611] LightSources
Organization: Ball State University
Hello,

         I have a 3D object which I want to show from different
viewpoints.  As the viewpoint changes I want the colors to remain the
same to facilitate comparisons.  Mathematica keeps it's RGB color
sources in fixed positions in terms of the display, thus the colors
change as one changes the viewpoint.  The solution would seem to be
move the lightsources so that the lights are in the same position
relative to the object as the viewpoint changes.  I am having trouble,
however, figuring out how to convert display coordinates to viewpoint
coordinates so that I can properly place the lights.  If anyone has
already done this or has any other ideas I would appreciate hearing
them.

Thanks

Alex

P.S. I have Mathematica 3.0
Alex Tabarrok
Department of Economics
Ball State University

******************************************************* From: Martin
Kraus <mkraus at theorie3.physik.uni-erlangen.de> To:
mathgroup at smc.vnet.net
Subject: [mg14440] [mg10120] Coordinate system of LightSources Organization: Univ.
Erlangen-Nuernberg, Theoret. Physik III Hello,
working on "Live.java" I am trying to find out how to simulate the
lighting done by Mathematica. Does anyone know in which  coordinate
system LightSources are defined? Or where this is explained? Ok, I know
this is answered in the Mathematica book. Thus here are some questions
which are connected with the question above but not answered by the
Mathematica book:
Why (and how) does the length of ViewPoint influence the lighting? (Does
it just quench the space in the direction of ViewPoint?)  Why is the
polygon in the following example not gray?
Show[Graphics3D[Polygon[{{0,0,0},{1,0,0},{1,0,1},{0,0,1}}],
ViewPoint->{1,0,0},PlotRange->{{0,1},{0,1},{0,1}},
LightSources->{{{1,0,1},RGBColor[1,0,0]},{{1,0,-1},RGBColor[0,1,1]}}]];
Currently my answers (as programmed in "Live.java") are: The lighting
should not depend on the length of ViewPoint. The polygon should
begray. I am not suggesting to change these things (bugs?) in
Mathematica  (its far too late). However I would like to be able to
simulate them. Thanks for any response

Martin Kraus



  • Prev by Date: Inserting/Removing Forced Page Breaks?
  • Next by Date: Re: Re: Error in CrossProduct...
  • Previous by thread: Re: Inserting/Removing Forced Page Breaks?
  • Next by thread: Re: LightSources