simplify(1pf)

NAME
     simplify - Interactive OpenGL Performer tool for simplifying geometry.  a
     simplification of a complex object that contains the original object.

SYNOPSIS
     simplify [ perfly options ] infile outfile [ options ]

DESCRIPTION
     Program simplify is an interactive tool that is used to simplify a
     complex object. It has two main functions. First, it can create a regular
     simplification of the object, in which the constraints are that the
     resulting geometry does not cross the inner and outer boundary at a
     certain distance from the original surface. In this case all vertex
     parameters, such us the normal or texture coordinates, are preserved.
     Simplified version of the object can be used to create an pfLOD node (see
     the man page for pfLOD).

     Second, the program simplify can create a proxy of an object.  A proxy is
     a simplified version of the object and it has a property that the
     original object is fully inside the proxy.  This property is important
     because the proxy is used in image based rendering where the images of a
     complex objects from various directions are projected onto the proxy.
     This way it is possible to render a very complex object using a
     simplified version (a proxy) and store the surface detail, including the
     associated lighting, in multiple textures.  See the man page for
     makeProxyImages to get more information about the process of making the
     textures that are projected on the proxy.

     The program simplify is based on perfly and it shares all its command
     line parameters and key commands (see man page for perfly). When
     executing the program simplify you can specify the perfly-like command
     line parameters first, then you enter the file name of the object you
     want to simplify and the output file name. Optionally you can add
     additional command line parameters specific to the simplification
     algorithm.  You can get the list of those parameters by running simplify
     with no option or option -h.

     When you start the program simplify the menu is similar to the one of
     perfly. There is an additional pane of buttons and sliders, called
     simplify pane, that can be enabled and disabled using the Simplify pane
     button. The first button of the simplify pane controls whether to select
     the algorithm for making proxy (the default) or the regular object
     simplification algorithm.


     MAKING PROXY OF AN OBJECT

     The algorithm for computing the proxy has two steps.  First, an outer
     boundary at certain distance from the object is created and an initial
     proxy somewhere between this boundary and the original surface is also
     created.  Second, the initial proxy is simplified as long as it does not
     intersect the original surface and does not cross the outer boundary.
     After completing the computation the proxy is saved in the file specified
     on the command line.

     There are two possible ways of creatin the outer boundary and the initial
     proxy. By default, a marching cubes algorithm is used to create an
     isosurface at a certain distance from the original object. The isosurface
     is later moved to the distance of the outer boundary (slider Outer
     boundary) and a copy of the isosurface is moved to the distance of the
     initial proxy (slider Initial distance).  The distances are specified as
     a percentage of the object diameter (more precisely, the diameter of the
     object's bounding sphere).

     The marching cubes algorithm has the following controls. In the menu it
     is possible to set the grid size at each axis and the distance of the
     isosurface from the object (slider Iso distance).  The finer the grid the
     longer the algorithm takes and the more complex the initial proxy is. On
     the other hand, too coarse grid may result in many details being missed.
     Note that even when the marching cubes algorithm is not applied the grid
     is used to accelerate the intersection test of the simplified proxy with
     the boundary surfaces thus it is not recomended to reduce the grid
     resolution too much.

     In general, the algorithm does not work very well if the desired
     isosurface distance is too small compared to the size of a grid voxel.
     That is why it is possible to specify the isosurface distance separately
     from the outer boundary distance and the initial proxy distance. Often it
     is possible to specify the isosurface distance large enough that the
     isosurface does not miss any part of the object and then move it closer
     as needed. It is also possible to preview the isosurface by pressing
     button Get isosurface. Note that the button Show boundary has to be
     depressed.

     When button Do marching cubes is not pressed, the outer boundary and the
     initial proxy are created by displacing the original surface along its
     normals. This approach works better in case the distances are very small.
     Unfortunately, some areas of the object may not be simplified. For
     example, if two parts of the object are touching displacing along the
     normals will create a self-intersecting boundary that will not allow any
     room for simplification in the area of intersection.

     After pressing the button Run simplify proxy the simplification algorithm
     starts by moving the isosurface or the original surface to create the
     outer boundary and the initial proxy.  The initial proxy is simplified by
     removing vertices and edges as long as the surface is within the surfaces
     defined by the object and the outer boundary.  At the end the vertices of
     the proxy are moved as close to the original object as possible and the
     resulting proxy is stored in a file.

     The simplification algorithm can be stopped or paused using Stop simplify
     or Pause button, respectively. When the algorithm is paused it is
     possible to output the current proxy by pressing the Save mesh button.
     The file name contains index of the current step so that several meshes
     can be output during the simplification.

     SIMPLIFYING AN OBJECT

     The controls for the regular simplification algorithm are very similar to
     the controls for the algorithm for making proxy.  The algorithm is using
     two boundary surfaces, the outer boundary and the inner boundary. If the
     marching cubes algorithm is selected the distance of the both boundaries
     from the original surface is the same (in absolute value) and it is
     controlled by the slider Iso distance.  Similarly as in the case of
     making a proxy the isosuface can be previewed by pressing the button Get
     isosurface.  If the Do marching cubes button is not pressed the
     boundaries are created by moving the original surface along its normals
     to distances specified by the sliders Outer boundary and Inner boundary.
     Note that the distance for the inner boundary is specified as a negative
     number.

     The algorithm is started by pressing the button Run simplify.  The
     computation can be paused or stopped using the Pause or Stop implify
     button, respectively. When the algorithm is paused it is possible to save
     the intermediate result by pressing the button Save mesh or to toggle the
     visibility of the boundary by pressing the button Show boundary. After
     the simplification is finished you can display the original object by
     pressing the button Restore object.  You can restart the algorithm
     without restoring the original object.

     As you may realize this algorithm could be used to create an object proxy
     if the marching cubes algorithm is not used and the inner distance is set
     to zero. The result may be different, though, because the algorithm is
     trying to preserve seams between pfGeoSets with different pfGeoStates,
     which is not necessary for the proxy.


SEE ALSO
     performer, pfIBRtexture, pfIBRnode, makeProxyImages