Re: LightSources

*To*: mathgroup at smc.vnet.net*Subject*: [mg14474] Re: [mg14440] LightSources*From*: "Jens-Peer Kuska" <kuska at linmpi.mpg.de>*Date*: Fri, 23 Oct 1998 20:58:52 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Hi Maarten, at first, if You need a rotated object (model coordinates) in fixed world coordinates (where ViewPoint & LightSources are) You may use the Graphics`Shapes package with its the RotateShape[] function. Tom Wickham-Jones ("Mathematica Graphics ...") has a function ViewPointFromUser[], ViewPointToUser[] in the packages of its book (View3D.m package) that convert between the model and the world coordinates. I expect that you can use the same functions to convert the light positions. You may find the package on MathSource . My book has a similar function for the calculation of line colors in depenence of the ViewPoint distance. You may find the informations about the book at http://www.mpae.gwdg.de/~kuska . Finaly my MathGL3d program let You rotate/spin the 3d object with fixed light sources (Menu or Spin, Rotate) You may find the program on my www-page http://www.mpae.gwdg.de/~kuska/mview3d.html with binaries for MS-Windows, Linux and Solaris. There You can find the 1.2 Version. The 2.0 Version is finished and will be available next week for all systems. Hope that helps Jens -----Original Message----- From: Maarten.vanderBurgt at icos.be <Maarten.vanderBurgt at icos.be> To: mathgroup at smc.vnet.net Subject: [mg14474] [mg14440] LightSources > >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 To: mathgroup at smc.vnet.net >Tabarrok <00attabarrok at bsu.edu.bsu.edu> To: mathgroup at smc.vnet.net >Subject: [mg14474] [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 To: mathgroup at smc.vnet.net >Kraus <mkraus at theorie3.physik.uni-erlangen.de> To: >mathgroup at smc.vnet.net >Subject: [mg14474] [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 > > >