3D Printing Research

File formats commonly used for 3D Printing

.stl

wikipedia: 
STL files describe only the surface geometry of a three-dimensional object without any representation of color.

stl files are common
http://3dprintingforbeginners.com/3d-model-reposit
https://all3dp.com/best-sites-free-stl-files-3d-printi
http://3dfilemarket.com/ (no reg required)

Article on the stl file format
https://all3dp.com/what-is-stl-file-format-extension-3d-printing/

Summary here:

its the most common format in 3D printing
it uses a series of linked triangles to create the surface model of 3D geom

Obviously - the more detailed the model, the more triangles required and the larger the resulting stl file

each triangle is described by 3 vertices and a Normal (to define the facing direction) perindicular to the triangle face.

"An STL file provides a complete listing of the x, y and z coordinates of these corners and perpendiculars."

STL is just a container for a model - it doesnt guarantee a virtual object will be printable

format:
An ASCII STL file begins with the line

solid name 

each triangle is then specified with

facet normal ni nj nk
    outer loop
        vertex v1x v1y v1z
        vertex v2x v2y v2z
        vertex v3x v3y v3z
    endloop
endfacet

where each n or v is a floating-point number in sign-mantissa-"e"-sign-exponent format, e.g., "2.648000e-002" (noting that each v must be positive). The file concludes with

endsolid name


9 Important printing concepts:

main benefits for STL:
simplicity
even complex designs can be reduced down to a series of triangles
the format is human readable

Drawbacks:
surface info only - no colour, texture, substance, sub-structure info is kept in a STL file
no metadata - no securtiy features

A stl file has to opened in a dedicated slicer ie Cura for the mac
https://ultimaker.com/en/products/cura-software

- a piece of 3D software to convert the triangles
into printing instructions for the the printer.

the slicer chops up your STL file into hundredds or thousands of flat horizontal layers (slices) based on the settings you choose and calculates how much material/ filament your 3D printer will need to extrude and calculate how long it will take to do it