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The staff of the Geometry Center is proud to announce release 1.3 of geomview, an interactive viewer for 3- and 4-D geometric objects built on OOGL, an object-oriented geometry library. Geomview is loosely a successor of our earlier program MinneView, and the current OOGL libraries have many new features. To clarify the difference between geomview, OOGL, and MinneView: geomview is an application written using the OOGL libraries as a foundation. You could write an application that uses OOGL that has nothing to do with geomview, but geomview would be useless without the OOGL libraries. The new version of OOGL retains the same name as the old. Geomview and MinneView are both viewers: geomview is newer and is different enough from MinneView we are considering it a different program and have changed the name, instead of regarding it as just "the new version of" MinneView. Geomview, OOGL, and MinneView run on Iris workstations using Silicon Graphics GL. A Next version of geomview and OOGL using Quick Renderman and a Sun X-windows version of them using XGL are under development. Geomview and OOGL are part of an ongoing effort at the Geometry Center to provide interactive 3D graphics software which is particularly appropriate for displaying the kinds of objects and doing the kinds of operations of interest in mathematics research and education. You can compute an OOGL data file of a mathematical object that would be difficult or impossible to build a model of in the real world. In geomview, besides examining an object in ordinary Euclidean 3-space, you can look at objects in hyperbolic 3-space and Euclidean 4-space. The hyperbolic model is the projective one, where geodesics are straight lines and isometries are represented as 4x4 projective matrices. While geomview is tailored for mathematical visualization, it is written to be extensible and can serve as a general-purpose tool. Its functionality can be extended in an almost unlimited fashion by external modules or programs as described below. The most basic way to use geomview is to interactively examine geometric data loaded from pre-computed files written in one of the OOGL file formats. Geomview turns numerical data that specifies an object or a world of objects into a scene in one or more graphics windows on your workstation. The most direct way to interact with this world is by moving the objects around and changing your point of view using the mouse. There is a control panel that allows you to change various aspects of the world. You interactively control the appearance and motion of the objects and the motion of the points of view. Multiple objects can be manipulated independently and there may be several windows looking at the same scene with different points of view. OOGL data files can be generated by a C program, written by hand, or converted from Mathematica 3D graphics objects using the conversion package that is also available via anonymous ftp. In the old version of OOGL, files could only specify geometry. Object file formats in the new version have been extended to also include appearances, transformations, and cameras. Any object appearance that you can establish through the geomview control panel can also be established by including an appearance specification in the same data file as that object. A path of motion can be specified in a file by a list of 4x4 transformations, allowing you to compute a path that would be very hard to trace freehand with the mouse. Geomview allows you to hook up the motion of an unlimited number of individual objects to separate transform files while keeping others under interactive control. Almost everything else that can be done interactively through the graphical user interface in geomview can be specified by a lisp-like command language. At present it has only viewer controls, no variables nor control structures. Data in any of the file formats described above (geometry, appearances, transforms, cameras) can be embedded within the language. Geomview can read in and act on a command language file at any time during an interactive session, and will automatically look for a file named ".geomview" in your home directory to configure itself when it starts up. Finally and most importantly, geomview can act as a graphical front end for a separate application. Besides interactive control or reading from a file, geomview can also be driven by external programs by reading through a Unix pipe. Anytime that you can read data from a file in geomview you could hook up a pipe. Meanwhile, interactive controls still apply to all features not being externally controlled. For example, hooking up a pipe to a geometry allows the viewer to show a simulation's dynamically changing output, while hooking up a pipe to the motion of a geometry allows externally-driven animation. The most general route is for an external program to send commands through a pipe, since all other file formats are a subset of the command language. Also one can externally supply geometric objects and transformations, changing all or part of a geometric hierarchy on the fly. Another new feature of the OOGL libraries, support for four dimensional data types, was implemented by Charlie Gunn. All geometric primitives, such as polygons, meshes, and vector lists, now can be supplied with either 3 or 4 dimensional vertices. The extensive use of projective coordinates in computer graphics allows the addition of this support with minimal programming effort. Geomview comes with an external module which allows the user to apply four dimensional rotations to these objects. The 4-D objects are shown in 3-D by projection rather than by slicing. We strongly encourage mathematical programmers to consider using geomview as a front end for graphics. Just as a text editor allows you to concentrate on the content of your program instead of the mechanics of displaying letters on a computer screen or an efficient algorithm for recalling previously cut text, geomview offers a way to incorporate visualization into mathematical programs without sinking huge amounts of time and energy into graphics programming. For users familiar with MinneView, here are the major differences between geomview and MinneView in a nutshell: Geomview has an easier-to-use user interface, multiple objects with independently controllable motion and appearances, multiple windows for different views of the same world of objects, different keyboard shortcuts, camera fly and orbit interactive motion modes, 4D support, and a lisp-like command language that allows external control of the viewer's state (actually a superset of what can be done interactively with the mouse). External programs that that use shared memory will need updating to work. The OOGL libraries now allow communication of geometry, appearances, transformations and cameras between programs, which is supported by extensions to the OOGL object formats. Arbitrary portions of hierarchies may be transmitted; the process involves creating references to named items, then transmitting values for those names. Similarities between the two are: all old OOGL files that MinneView could read can be used by geomview. The object motion modes rotate, zoom, and translate still exist. External programs that used "stuff", a program that stuffs geometric data into a named pipe, to communicate with MinneView should work unchanged with geomview. Geomview may be obtained via anonymous ftp from geom.umn.edu; it is in the "pub" subdirectory in the file "geomview.tar.Z". After retrieving it (in binary ftp mode), the command "uncompress < geomview.tar.Z | tar xvopf -" will unpack it into the current directory. This distribution includes binaries, documentation, and sample data files for geomview and a collection of auxiliary programs. See the file README for details after unpacking. Please send all correspondence regarding this software via email to "software@geom.umn.edu". ------------------------------------------------------------------------ Stuart Levy Tamara Munzner Mark Phillips
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