Is it possible to constrain a models polygon geometry?

Wondering if anyone knows of modeling software that allows the geometry of the polygons (Triangles) within a model to be constrained to specific lengths? I am building paper polygon sculptures and would like to use software to help me determine the dimensions of the individual polygon shapes. Specifically, I'd like to constrain the geometry of the polygon shapes to only allow specific increments, for example: 3 cm, 6 cm, 9 cm, 12 cm etc. Does anyone know of software that allows this kind of control?

Thanks.

hi marbank,
many 3d packages work in generic units, which can be a little difficult to grasp at first if you are looking for real world units. basically 3d scenes are divided up into grids, one grid unit could be used to represent any real world dimension (such as 3cm) as a result if you turn snap to grid settings on in your 3d packages view port (asmost 3d packages will have this option) you will be moving sub-level geometry (such as triangles, edges, verts etc) in the equivalent distances of your chosen real world unit. the main rule with regards to working like this is that you obviously cannot change the unit that a grid measurement represents for that project. it's also a good idea to leave snapping on so that object level data also gets transformed (scaled, translated etc) uniformly and according to the same unit of measurements. hmmm i hope i explained that properly?