A model for non-isometric changes in growth was given by Bernard Tursch in his paper Spiral Growth: The 'Museum of all Shells' Revisited (Laboratoire de Bio-Ecologie, Faculty des Sciences, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, 1050 Brussels, Belgium, March 1997). Here I propose another way, that perhaps more closely follows morphological changes using growth curves, as opposed to a geometric growth factor. The intention of using growth curves is to model ontogentic changes over time more precisely. Growth curves are best applied to isometric forms where R = L = W.
Whorl Edge Growth Curve
This growth curve is used to change the leading edge of each stack along the direction of growth. To activate the curve, click the curve toggle on the Generator so that it lights yellow:
Two separate curves may be applied to each side of the profile. For a symetrical profiles, ensure that 'Reflect' is checked in the Curve window:
Whorl Growth Curve
This growth curve is used to change the size of the whorl in a direction that is perpendicular to the line of growth. Below: a whorl growth curve that results in a concave spire:
Below: a whorl growth curve used to make a concave spire in a long turret type shell:
Below: a whorl growth curve used to accelerate shrinkage towards the aperture of the form.
Alternatively, a literal curve may be applied to the stacks. See Stacks Profile Editor for more information.