[Raytrace] Where To Start?

[John D. Upton]

List,

     Our membership seems to be pretty stable now at about 35.  Let's get 
going.

     Where do you want to get started on this list?  I don't know exactly 
what level of knowledge already exists, so I am unsure.  What do you want 
to discuss?  One possible starting point is to discuss things common to all 
ray-tracing programs -- or whether there is anything in common.

     For starters, do all programs use the same conventions for data entry?

     OSLO uses a "spreadsheet" format.  If you draw out a design on paper 
with light starting from the left, the following rules apply.  Are these 
basic rules the same for all other programs we might be interested in using?

1.  Each surface encountered by the light is numbered in the order that the 
incident light transverses it.  If the light is reflected back onto a 
previous surface, it is numbered again, but the parameters can be picked up 
from the original specification.

2.  If light is travelling left to right, distances are positive.  If right 
to left, they are negative.  At each reflection, the sign of the directions 
changes.  (For example; if light is going left to right, the sign of 
distances is positive.  If that light is reflected, the next distance is 
negative.  If it is again reflected, the sign changes back to positive.)

3.  Each surface has a radius of curvature, aperture, thickness, and media 
associated with it.  Surfaces may also have special data such as conic 
constant associated with them.  The thickness and media are understood to 
be where the light is entering upon traversing the surface.

4.  For a curved surface, if the center of curvature is to the right of the 
surface, the ROC is a positive number.  If the COC is to the left of the 
surface, the ROC is a negative number.

5.  Each surface has a thickness associated with it.  The thickness is 
simply the distance to the next sequential surface.  Lenses have a 
thickness to them, of course.  Air spaces are also considered "thicknesses".

    Are these basic rules the same in all programs?  They seem to be 
consistent with all the optics and ray-tracing texts I have read.  What 
other "rules" might be considered common to most if not all programs?

John D. Upton
Georgetown, TX
<http://www.atm-workshop.com/>     "The ATM's Workshop"
<http://members.aol.com/RonWin20/> "Ronchi For Windows Home Page"