Re: [Plib-users] Shadow

[<Ran...@ma...>]

Steve Baker writes:
 > 
 > Ran...@ma... wrote:
 > 
 > NO!!!  You are seeing a 'mach band' which is an optical illusion that
 > will happen the same way in your program as it does in the real world
 > and doesn't have to be simulated.
 > 
 > There is no significant angle-of-incidence effect for most materials.

Dredging up the stuff from a previous incarnation, the "hotspot" isn't
an optical illusion, rather it is related to the amount of visible
shadow (cast by protruding objects on the surface) relative to the
amount of visible, directly illuminated surface.  You are right -- the
hotspot will appear without any additional code if the surfaces do in
fact have a vertical texture (that was what my former incarnation
depended on).  In my mind I was imagining that the the surfaces we
were talking about were textured with texture maps, rather than
something with real vertical texture.

It isn't an optical illusion -- you can use the size and intensity of
the hotspot to elicit information from aerial photography about the
size of (for example) trees in a stand and their mean distance apart.
Real empirical science ... I can provide a few (old) references for
those that are interested.

Randall