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