Beyond Gnuplot: An introduction to POV-Ray

Transcription

1 Beyond Gnuplot: An introduction to POV-Ray Timothy Jones Drexel University May 28, 2008

2 What is raytracing? Step 1: Get a light source.

3 What is raytracing? Step 2: Get a camera.

4 What is raytracing? Step 3: Get an object.

5 What is raytracing? Step 4: Ray trace.

6 What is POV-Ray? The Persistence of Vision Raytracer a freely available leading free raytracer. Ray tracing origins: In the 1980s, David Kirk Buck (real name) hacks around with the ancient Unix raytracer Amiga, eventually deciding to write his own version. He creatively calls it DKBTrace. Posted on ancient communication device called bulletin board system. Snowballs into POV-Ray. Street-cred: First raytracer to render an image while in space (rendered by astronaut Mark Shuttleworth on the ISS); used by Intel to demonstrate new processors, etc.

7 Get it right. POV-Ray is free software, not open source. If you don t know the difference, you probably have a life.

8 Features Lots of technical features of interest to graphics designers. Makes great use of classical optics. Many features consume a lot of processor time, thus I don t use them for my simulations, just the basics. POV-Ray is well documented on-line.

9 Known knowns and known unknowns What POV-Ray can do: Improved photo-realism via ray-tracing (an important part of the evolved human visual system) Better feel for data and easier presentation Animation for extra dimension What POV-Ray can t do: Plots aren t typically journal-quality (too 3D) Sophisticated visualizations (like masking) available in such programs as VISIT aren t pre-programed.

10 An example from the internets The famous Utah teapot: POV-Ray uses more sophisticated algorithms than simple photon raytracing, including radiosity and other optical effects, and focal blur and other camera effects.

11 The finest example: Glasses by artist Gilles Tran

12 Practical examples: Algebraic Topology figure Goal: To create a visualization of the concept of contractibility via space homotopy to a single point. First we set the lighting, background, and camera position and angle. camera { location <0.5, 0.8,-5> look_at <0,0,0> } light_source {<0, 20, -30> color White} light_source {<0,-10,-500> color White} background {rgb <1,1,1>}

13 Practical examples: Algebraic Topology figure Build up the blob space. We use spheres and the blob function of POV-Ray. The threshold gives us a measure of blobiness. blob { threshold.65 sphere { <.5,0.3,0.2>, 0.5, 0.5 pigment {Yellow} } sphere { <0,0.6,0>,1.3, 1 pigment {Red} } sphere { <0.5,1,-0.5>,0.8, 0.5 pigment {Yellow} } sphere { <-1,0.7,0>, 1, 0.5 pigment {Gold} } texture{glass} finish { phong 0.8 } }

14 Practical examples: Algebraic Topology figure Finally draw a few homotopy paths (in this case the problem called for a composition of functions). We use cylinders to show these paths and a sphere to mark our single-point. sphere {<0.2,0.4,-1.5>,0.05 pigment{black} finish { phong 0.9 }} cylinder {<.5,0.3,0.2>,<0.8,0.2,-3>, 0.01 texture{pigment{color Green} finish {ambient 0.45 diffuse 0.55 phong 1}}} cylinder {<0.8,0.2,-3>,<0.2,0.4,-1.5>, 0.01 texture{pigment{color Blue} finish {ambient 0.45 diffuse 0.55 phong 1}}} cylinder { <0,0.6,0>,<-0.8,1.2,-3>, 0.01 texture{pigment{color Green} finish {ambient 0.45 diffuse 0.55 phong 1}}} cylinder {<-0.8,1.2,-3>,<0.2,0.4,-1.5>, 0.01 texture{pigment{color Blue} finish {ambient 0.45 diffuse 0.55 phong 1}}} cylinder { <0.5,1,-0.5>,<0.8,1,-3>, 0.01 texture{pigment{color Green} finish {ambient 0.45 diffuse 0.55 phong 1}}} cylinder {<0.8,1,-3>,<0.2,0.4,-1.5>, 0.01 texture{pigment{color Blue} finish {ambient 0.45 diffuse 0.55 phong 1}}} cylinder { <-1,0.7,0>,<-0.8,0.2,-2>, 0.01 texture{pigment{color Green} finish {ambient 0.45 diffuse 0.55 phong 1}}} cylinder {<-0.8,0.2,-2>,<0.2,0.4,-1.5>, 0.01 texture{pigment{color Blue} finish {ambient 0.45 diffuse 0.55 phong 1}}}

15 Practical examples: Algebraic Topology figure

16 Practical examples: Astrophysics (microlensing) A friend in astrophysics wants to give a really great postdoc job talk. He has a number of concept figures which POV-Ray could do quite well, and a friend who knows POV-Ray (me). To make a gravitational lens diagram such as he had, we use POV-Rays spline (generates smooth curve from discreet points) and lathe (generates by rotation) functions: #declare bottle = lathe { quadratic_spline 7, <29/40,2-(113-59)/59>, <22/40,2-(104-59)/59>, <14/40,2-(88-59)/59>,<7/40,2-(67-59)/59>, <3.8/40,2 -(47-59)/59>,<2/40,2 -(28-59)/59>, <0,3> sturm } #declare bottle2 = lathe { quadratic_spline 7, <29/40,2-(113-59)/59>, <22/40,2-(104-59)/59>, <14/40,2-(88-59)/59>,<7/40,2-(67-59)/59>, <3.8/40,2 -(47-59)/59>,<2/40,2 -(28-59)/59>, <0,3> sturm }

17 Practical examples: Astrophysics (microlensing) Since the figure is to be conceptual, and is used to discuss the analogy between classical lensing and gravitational lensing, we wish to give it a glass texture. We also wish to treat the two pieces created in the previous slide as one, so we use the union tag. Notice that POV-Ray is sophisticated enough that we can give ray transmission percentage (transmit) and index of refraction (ior) inputs. union{ object { bottle interior { ior 1.04 } pigment{color Yellow transmit.7} texture{glass} finish{phong.8} translate<0, ,0> } object { bottle2 interior { ior 1.04 } pigment{color Yellow transmit.7} texture{glass} finish{phong.8} rotate <180,0,0> translate<0,0.29+(2-(113-59)/59)-0.12,0> } rotate<0,0,90> scale<0.3,3.2,0> }

18 Practical examples: Astrophysics (microlensing) We can show the rays and sources using cylinder and sphere commands. The resulting figure compares well with the original.

19 Other figure examples...

20 Other figure examples...

21 Other figure examples...

22 Other figure examples...

23 Other figure examples...

24 Other figure examples...

25 Finally...all films are made up of frames. POV-Ray has built in animation routines that are incredibly easy to use. You can find many examples on my web-page: The complete set of codes for making these animations are made available for reverse engineering. The best of these animations has been compiled into a short film...