This section gives detailed information about the parameters
of the shell generator. All explanations are very theoretical.
If you cannot understand them, print the "Reference Sheet"
("doc/reference.ps"
) and try to find the parameter in question there.
Playing around with the GUI for some time might also be a good idea.
The basic idea of the algorithm is to simulate a shell shape by rotating a growing ellipse around the z-axis, and simultaneously displacing it from the z-axis. This results in a flat spiral. If we move the ellipse along the z-axis while rotating, a shell like shape will appear. The curve determined by all centers of all ellipses is a so called helico-spiral.
The parameters of this process are divided into 5 groups. Parameters that need to be given in degrees are marked with an asterisk ("*").
These parameters change the shape of the
helico-spiral ("alpha"
* and "beta"
*) and the tilt of
the ellipse against the axes of the local coordinate system of the ellipse
("phi"
*, "my"
*, "omega"
*). Note, that "alpha"
* does
determine the growth rate of the ellipse too.
They change the size (and shape) of the
ellipse ("a"
, "b"
) and the distance of the first ellipses
center from the z-axis ("A"
).
They set how many ellipses are calculated
("omin"
*, "omax"
*, "od"
*), and how many points
on each ellipse are calculated ("smin"
*, "smax"
*, "sd"
*).
Finally, a global scale-factor, independent from all file format specific
scaling, might be applied using "Scale"
.
Change all aspects of nodules, position on the
ellipse ("P"
*), size ("W1"
*, "W2"
*), length ("L"
),
number of nodules per whorl ("N"
) and starting point on
the spiral ("Nstart"
*).
There are three independent groups of nodules.
Add a "2"
to each nodule parameter to set parameters
of the second nodule group. Length of second nodule is therefore "L2"
.
Do the same for the third nodule, with a "3"
.
There are two more parameters to control an offset between the three groups
of nodules, "Off2"
* is the offset between nodule 1 and nodule 2 and
"Off3"
* is the offset between nodule 1 and nodule 3.
"Scano"
, "Scans"
, "Hdo"
,
"Hds"
refer to section
Calculation Modi
for information on this parameters.
The most important parameters are "alpha"
, "beta"
, "A"
,
"a"
and "b"
.
Here are some hints on how certain values change the shape of the shell.