What is an appropriate measure for a digital sculpture?

[Mxa75]

My apologies if my post is confused but I am a newcomer to this field, so the question may be trivial.

First of all, I am solely concerned with fine art and I assume that a "digital sculpture" will be made of one material - at least for the time being. For an application I am developing I need to find the equivalent, for a digital sculpture, of the number of pixels that is used in say a photograph to define its "size". Is there such an equivalent in a 3d printed sculpture? Do the software tools give you the total volume occupied by the sculpture (in that case cm^3 could be a good unit of measure)? Once you know the material, could one use grams instead? Does the software that drives a 3d printer give you the weight of the object?

Volume is better in that it is material-independent, but I am open to any other suggestion. Also, the volume should not include the empty space(s) *within* the sculpture but be the actual volume of the material being used. Again, do software tools like zbrush or mudbox give you this figure?

Thank you for your patience and again, sorry if the question is silly.

Any comment will be appreciated

Cheers

Marco

[Andrew Werby]

A digital sculpture can be saved in various different formats, so there isn't a single unit that will universally quantify it. If it's saved as an IGES file, for instance, the surfaces are mathematically defined in an economical way that lets it be scaled up or down without showing any faceting. Also, if it's just a surface, then it has no thickness; its weight in grams would be zero, no matter how big it was. Only when you "shell" it does the volume of material it would require to print become definable. The thickness of this shell is variable, so the same part could take more or less material. There are some programs that use "voxels", which are the volumetric equivalent of pixels, and these can be counted. But voxelized files account for only a small proportion of the digital sculptures out there.

The most universal format, though, is the STL file, which has become a de-facto standard in the printing industry since it's non-proprietary, even though it's fairly unwieldy. Mesh files, which consist of a series of triangles that define a surface, are often saved in this format, which basically records the vertex points that the triangles share. While the physical size of a sculpture that's made from these meshes can vary considerably, printing it larger will make each triangle bigger, leading to a faceted appearance in the piece. This triangle count is often given in a software program; it also has a close relationship to the overall file size. But a small sculpture can be meshed very finely, and have a large file size, while a large one could be meshed coarsely and have a small one.

It's not too hard to figure out the total volume of material your digital sculpture will require, if you use a program that calculates that, based on the size and thickness you decide to make it. And once you know the total volume, it's easy enough to calculate how much it will weigh, as long as you know the specific gravity of the material you plan to print it in. But there's no way to do this for every random sculpture in digital form, without making these decisions first.

Andrew Werby
www.computersculpture.com

[Mxa75]

Andrew,
thank you very much for taking the time to write such an outstanding contribution. You definitely made me make a huge step forward.
Cheers
Marco