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What is your qualm with calling ray-tracing physically based? Don't most models even include transmissivity and refraction? I mean, unless you're expecting the

by ctrl-j 8y ago

What is your qualm with calling ray-tracing physically based? Don't most models even include transmissivity and refraction? I mean, unless you're expecting them to calculate absorption/re-emission at every bounce... It still seems pretty "physical" to me.

toolslive 8y ago
Here you're using geometrical optics which models is a narrow beam (ray) which is idealized as a line. It all becomes simple vector math form there onwards. However, Physics knows since the end of the 18th century light is a wave. https://en.wikipedia.org/wiki/Young%27s_interference_experiment https://en.wikipedia.org/wiki/Young%27s_interference_experim... It's not that the model breaks down only in extreme conditions (like Newton's laws of mechanices), but in day to day situations as well. I think that's the essence of my qualm.
- ctrl-j 8y ago
  The wave-like nature of photons does not exclude the particle behavior. Light is both a particle and a wave. Physicists still rely on snells law. Optics courses still includes path tracing when studying refraction and dielectrics. Excluding the particle behavior of light just because the wave nature exists, is not something a physicist would do.
  - toolslive 8y ago
    True, but the concept of ray used here is neither particle nor wave. The whole thing is way more geometry than physics.
    - mattnewport 8y ago
      Would you say the same thing about rigid body physics simulations? There's no such thing as an idealized rigid body in reality but such simulations use lots of useful approximations the are also used in "real" physics.
    - ctrl-j 8y ago
      I mean, you're arguing a term that's used in physics isn't physical. Raycasting is often used when solving EM equations. Are you purporting that photon streams don't follow a ray? And when they interact with a surface they don't obey Snells law? And when you look at the interface between mediums a percentage of the intensity is transmitted and the remainder is reflected (the ratio of which is determined by the angle of incidence?)
- wnkrshm 8y ago
  Where in day-to-day situations, like walking around outside or in a building do you see diffractive phenomena where a ray approximation breaks down far enough for you to notice? Usually all of that is smoothed over by light sources being extended sources not points, so the interference contrast is lost by infinitely many interference patterns being overlaid incoherently. Also, almost all light sources (except for rlasers) have microseconds of coherent emission, so the pattern changes so fast it blurs into a regular blurry edge of shadow. I can only think of some very special situations where some blinds select a very narrow angular range of sunlight and then you see interference fringes in the shadow. Or when you look into a puddle with an oil film or at some sort of diffraction grating or holographic film (which can be predicted with ray-based methods, like Wigner-distribution based ray-tracing, though that still comes with some error at large angles). Even in laser optics, 95% of the optics design is done with geometrical optics methods, because the rays you use can be related to the phase profile of the radiation in the system. You can then integrate (with rays) the diffraction pattern (but not as well in the shadow of apertures ofc).
  - toolslive 8y ago
    plenty of examples, but https://en.wikipedia.org/wiki/Glory_(optical_phenomenon) https://en.wikipedia.org/wiki/Glory_(optical_phenomenon) is a pretty one.

by ctrl-j 8y ago

toolslive 8y ago

Here you're using geometrical optics which models is a narrow beam (ray) which is idealized as a line. It all becomes simple vector math form there onwards. However, Physics knows since the end of the 18th century light is a wave. https://en.wikipedia.org/wiki/Young%27s_interference_experiment https://en.wikipedia.org/wiki/Young%27s_interference_experim... It's not that the model breaks down only in extreme conditions (like Newton's laws of mechanices), but in day to day situations as well. I think that's the essence of my qualm.

ctrl-j 8y ago
The wave-like nature of photons does not exclude the particle behavior. Light is both a particle and a wave. Physicists still rely on snells law. Optics courses still includes path tracing when studying refraction and dielectrics. Excluding the particle behavior of light just because the wave nature exists, is not something a physicist would do.
- toolslive 8y ago
  True, but the concept of ray used here is neither particle nor wave. The whole thing is way more geometry than physics.
  - mattnewport 8y ago
    Would you say the same thing about rigid body physics simulations? There's no such thing as an idealized rigid body in reality but such simulations use lots of useful approximations the are also used in "real" physics.
  - ctrl-j 8y ago
    I mean, you're arguing a term that's used in physics isn't physical. Raycasting is often used when solving EM equations. Are you purporting that photon streams don't follow a ray? And when they interact with a surface they don't obey Snells law? And when you look at the interface between mediums a percentage of the intensity is transmitted and the remainder is reflected (the ratio of which is determined by the angle of incidence?)
wnkrshm 8y ago
Where in day-to-day situations, like walking around outside or in a building do you see diffractive phenomena where a ray approximation breaks down far enough for you to notice? Usually all of that is smoothed over by light sources being extended sources not points, so the interference contrast is lost by infinitely many interference patterns being overlaid incoherently. Also, almost all light sources (except for rlasers) have microseconds of coherent emission, so the pattern changes so fast it blurs into a regular blurry edge of shadow. I can only think of some very special situations where some blinds select a very narrow angular range of sunlight and then you see interference fringes in the shadow. Or when you look into a puddle with an oil film or at some sort of diffraction grating or holographic film (which can be predicted with ray-based methods, like Wigner-distribution based ray-tracing, though that still comes with some error at large angles). Even in laser optics, 95% of the optics design is done with geometrical optics methods, because the rays you use can be related to the phase profile of the radiation in the system. You can then integrate (with rays) the diffraction pattern (but not as well in the shadow of apertures ofc).
- toolslive 8y ago
  plenty of examples, but https://en.wikipedia.org/wiki/Glory_(optical_phenomenon) https://en.wikipedia.org/wiki/Glory_(optical_phenomenon) is a pretty one.