A 3D model can be outputted on a 3D printer if the model is watertight, that means there are no holes and non-manifold edges do not exist.
Prepocessing of 3D printing requires error correction, decimation of surfaces, cutting the model,
and scaling and positioning on the (virtual) printer ground plane.
A so prepared STL file will be send layer by layer in G-Code to the printing device.
Independent from the real printing process, preprocessing extents the quality of ths data base.
Meshmixer from Autodesk is a software for sculptureing and preprosseing.
It is possible with Meshmixer to unify meshes, generate solids from reliefs and correct errors.
An imported model will be analyzed and automatically corrected.
The final model can be exported in STL format.
Screenshot Meshmixer contour extrusion
Netfabb Studio is a software for slicing, positioning an preprocessing models for efficient printing. It is not designed for modeling. Slicing planes can be defined along all three co-ordinate directions and can be playbacked as animations or exported in SVG format. NetfabbStudio Basic is a freeware for the non-commercial field. The professional version has additional functions.
Meshmixer und Netfabb Basic both together are useful for finishing meshes. More little helpers are presented in the menu TOOLS.
Pictures:
Left top: Makerbot Replicator 2 Section
Right top: Filament
Right center:Section of a mesh
Right bottom:Slicing tool Netfabb