One of the goals of current computer graphics is to produce images
with as much realism as possible. To achieve this, there is not only
the need to improve old (or invent new) rendering techniques, but also
to enhance the scene. In the recent years hard work has been done to
make the modeling tools as comfortable and easy to use as possible.
An experienced graphic designer is capable of creating a 3D model of
almost any shape he can imagine. However, what good is an excellent
three-dimensional model if it is in the scene alone? To create a
realistic-looking scene it is necessary to place many entities at
proper places. It is the scene composition that often leaves in the
spectator the biggest impression. A brief glance at what support is
available to the scene designer to make a scene with many objects
constitutes an opinion that a mass-scene creation and rendering
tool would improve both the quality and the comfort of a 3D-scene
1.1 Typical mass scene
Typical scenes that have been considered during the design of the
mass-scenes creation tool include: characters in an audience, a
flock of birds, a lawn with blades of grass, trees in a forest,
a hairy monster, stalagmites in a cave, cars on a parking place.
If the scene author has enough time and patience, he might be able
to do a very nice mass-scene without any special instrument, but with
a great effort. Current modelling tools provide only two techniques to
clone an object: instantiating and referencing the particular object.
Although they are quite good to model small quantities of objects,
they are not sufficient for mass scenes. The aim of this paper is
to make the scene creation work much easier - what can be made by
the computer should be done by the computer without any painful,
long lasting or boring human assistance.
1.2 Instantiating an object
Instantiating is one of the basic operations that are in almost
all software products. It is often called copy & paste. This facility
makes possible to create a lot of instances, to place them into the
scene and later change their properties. Some modeling tools provide
functions to make the placement automatically - in a row, on the circle,
or even some more sophisticated layouts.
1.3 Referencing an object
Referencing is almost the same as instantiating. The only difference
is that if an object is cloned as a reference, after making a change
in the original object, all the references are changed too. This has
a big advantage if there are changes to be made after the objects have
been cloned. E.g. the author forgot to add eyes to a creature that has
already been cloned hundred times. After adding the eyes to the master
(original) object, all the slaves (references) receive their own eyes
These two techniques have one main disadvantage - all the changes to
the clones are to be done by the designer. The computer only makes the
clones that are exactly the same as the original. However, for a
realistic look the instances must differ in some details.
Due to the lack of time or patience, the author of the scene alters
only a scarce number of the instances. At the first glance the result
seems to be quite nice and fulfilling the intention, but after a short
observation the objects seem to be somehow periodical and disturbingly
regular, the scene is not as realistic as should be.
1.4 Special modeling techniques
A lot of hard work has been devoted in the recent years to some
special types of mass scenes and parametric descriptions of objects.
The results have usually the same basic scheme - the object to be
modeled is considered from two points of view, the first is how an
instance of the object can look like, and the second is how the
instance behaves in an area or as a part of a whole entity. Then
a tool is developed that confirms the assumptions. An example of
such paper is  where the authors studied plant ecosystems and
then rendered scenes consisting of thousands of generated plants
in amazing photo-realistic quality. Another example is the modeling
of human hair  by making a physical model of human hair, and thus
generating the whole head.
Also the movie producers have their own special modelling tools that
are many times developed exclusively for a desired type of scene. For
instance the famous company Pixar developed in 1998 for the movie
A Bug's Life new methods for modelling and animating large crowds
of figures, but they keep their technical information in secret.
Nevertheless, all these modeling techniques are quite specialized
for a particular type of scene. This paper introduces a technique
that is not dependent on the scene type; it is a tool that is
applicable on most mass scenes. On the other side it cannot compete
(in the image quality) with a very special modeling tool, but this
small handicap is counterbalanced by the generality of the approach.