"Bald Eagle" <cre### [at] netscapenet> wrote:

>
> I made boxes with a frequency of 1/pi, and did the same 5-degree phase shift per
> box.  It gives you the same "backwards" shift,
> BUT
> if you think about what sin(x+_phase) would give you as you increase _phase,
> then I suppose it makes sense...
>

The general *meaning* of 'phase' (or rather, which 'direction' is meant by a
'phase shift') is somewhat difficult to grasp, for me-- how to describe whether
a phase shift is in the positive or negative direction. It's kind of relative to
the initial position of the waveform.

I looked up 'phase' in Wikipedia, and even that overall description isn't quite
clear to me. In the following excerpt, I'll substitute 'P' for the phase symbol
(or phase shift-- it's not clear)...

"Phase shift is...the phase difference between two or more quantities.

The symbol P is sometimes referred to as a phase shift or phase offset because
it represents a 'shift' from zero phase.

For infinitely long sinusoids, a change in P is the same as a shift in time,
SUCH AS A TIME DELAY. If x(t) is delayed (time-shifted) by 1/4 of its cycle
[DELAYED in time], it becomes:
    --- some mathematical jargon---
whose 'phase' is now P - pi/2."

I.e., that's a *negative* phase shift-- which would seem to correspond to
POV-Ray's concept of, say, phase 0.25 or whatever-- POV's 'positive' phase
change, but one which shifts the waveform itself in the negative direction.

But the accompanying diagram in that block of text shows the original waveform
in red, and the shifted waveform in blue-- and the blue one is shifted FORWARD
in time-- which looks like the opposite of 'P - pi/2'.  What a brain-twister!

Post a reply to this message