3dcanvas is an old project (1996 and Tk4.2) introduced by Peter Loborg at:
http://www.ida.liu.se/~petlo/3D_canvas/
This widgets implement a three dimensional space in which structured graphics can be rendered. A 3dcanvas displays any number of items, which may be things like spheres, polygons, lines and prisms. Items may be manipulated (e.g. moved or re-colored) and commands may be associated with items in much the same way that the bind command allows commands to be bound to widgets. The 3dcanvas also contains a powerful grouping mechanism for manipulating several spatially related objects as one.
The objects in a 3dcanvas are stored in a hierarchical database together with associated relations and attributes. This hierarchy is constructed using a special item type called the group item, which is capable of containing other items including group items.
In the 3dcanvas, all items have their own coordinate system, which is relative to that of it’s parent group (this is the group in which the item is currently placed). All transformations such as scaling or rotating is performed on this local coordinate system. This means that if a group is rotated, it’s coordinate system will be warped, and so will that of every contained item as their coordinate systems are specified in terms of the groups coordinate system.