(From Blob Sculptor documentation)
In 1982 J.F. Blinn modeled molecular shapes using an object
which consisted of a point (the center of the object) and a radial field
which decayed exponentially as a function of the distance between any
given point in space and the center of the object. A test point near to
the center of this object would have a very high potential field. As
this point was moved outward, its potential field would reduce until, at
a given distance R (the radius) it would go to zero. This object is
called a "Blob".
Blobs consists of an arbitrary number of objects, called
"components" which interact with each other. A "spherical component" is
a blob component which has the geometry of a sphere (there are
cylindrical, and conical components too!). In order to find the
interaction between all the components of a given blob, a test point in
3D space is evaluated in terms of the potential field that EACH
component contributes. The individual potential field of a component is
called it's "density" or "strength". This strength can be positive or
negative. Once all the contributions of all the components for a given
test point are calculated, they are added up. Since some of the
strengths may be positive or negative, the object may or may not have a
value at the test point.
Finally, in order to know if that point in the object will be
part of the final surface, the total strength of that point is compared
against a "threshold" value. If the strength >= threshold then the
point exists, else it dissapears. The threshold value can be thought of
as a filter; the higher the threshold, the stronger the blob component
must be in order to visible.
Once all the points in space are calculated, an algorithm called
"marching cubes" is used to convert this 3D values into surfaces.
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