STLA Files
ASCII stereolithography files

These are some examples of STLA, or "ASCII STL" files. "STL" stands for "stereolithography", and indicates that the primary purpose of this file format is to describe the shape of a 3D stationary object. Stereolithography is a means of creating physical 3D models of such objects, using resin or carefully cut and joined pieces of paper.

An ASCII or binary STL file usually has a filename extension of ".stl". To avoid confusion, we use a filename extension of ".stla" for ASCII STL files; however, this is not a common convention. It may be advisable to rename a ".stla" file to the more conventional ".stl" before passing it to a graphics utility program.

An STL file contains a description of the surface of a solid that has been decomposed into triangles. The vertices of the triangles should be listed in counterclockwise order, as viewed from outside the surface. A normal vector for the triangle may also be listed.

The file begins with a solid record, (which can include a name for the object), and ends with an endsolid record. Each triangle begins with a facet record and ends with an endfacet record. The normal vector, if given, is included as part of the facet record, and is identified by the normal keyword. The normal vector should have unit length. The three vertices of the triangle are delimited by outer loop and endloop records. Each vertex is described on a vertex record that lists its (X,Y,Z) coordinates.

An ASCII STL file for a four-face figure that's a slice of a cube would be:

        solid cube_corner
          facet normal 0.0 -1.0 0.0
            outer loop
              vertex 0.0 0.0 0.0
              vertex 1.0 0.0 0.0
              vertex 0.0 0.0 1.0
            endloop
          endfacet
          facet normal 0.0 0.0 -1.0
            outer loop
              vertex 0.0 0.0 0.0
              vertex 0.0 1.0 0.0
              vertex 1.0 0.0 0.0
            endloop
          endfacet
          facet normal 0.0 0.0 -1.0
            outer loop
              vertex 0.0 0.0 0.0
              vertex 0.0 0.0 1.0
              vertex 0.0 1.0 0.0
            endloop
          endfacet
          facet normal 0.577 0.577 0.577
            outer loop
              vertex 1.0 0.0 0.0
              vertex 0.0 1.0 0.0
              vertex 0.0 0.0 1.0
            endloop
          endfacet
        endsolid
      

The facet record has the form:

• The normal vector, 3 floating values of 4 bytes each;
• vertex 1 coordinates, 3 floating values of 4 bytes each;
• vertex 2 coordinates, 3 floating values of 4 bytes each;
• vertex 3 coordinates, 3 floating values of 4 bytes each;

STLA File Characteristics:

• 3D;
• ASCII;
• No color information;
• Normal vectors are associated with faces;
• Triangulated surfaces;
• No compression;
• 1 image;

Related Data and Programs:

STLB is a binary version of the ASCII STL file format.

Reference:

1. 3D Systems, Inc,
   Stereolithography Interface Specification,
   October 1989.

Programs to read an ASCII STL file:

• STLA_IO is a library which contains a routine to read in an ASCII STL file. This library is available in a C++ version and a FORTRAN90 version and a MATLAB version.
• STLA_READ_FAST is a MATLAB routine which can quickly read in an ASCII STL file.

Programs to write an ASCII STL file:

• STLA_IO is a library which contains a routine to write out an ASCII STL file. This library is available in a C++ version and a FORTRAN90 version and a MATLAB version.

Programs to view an ASCII STL file include:

• STLA_DISPLAY is a MATLAB program which can read an STLA file and display it on the screen.

Programs to convert an ASCII STL file to another format:

• IVCON is an executable C++ program which can read in an ASCII STL file and write it out in a variety of 3D formats.
• IVREAD is an executable FORTRAN90 program which can read in an ASCII STL file and write it out in a variety of 3D formats.
• The Visual Toolkit routine vtkSTLReader can read an ASCII STL file.

Programs to convert another format to ASCII STL format:

• IVCON is an executable C++ program which can read a variety of 3D files and write them out in ASCII STL format.
• IVREAD is an executable FORTRAN90 program which can read a variety of 3D files and write them out in ASCII STL format.
• The Visual Toolkit routine vtkSTLWriter can write a VTK image to an ASCII STL file.

Sample STLA Files:

BLOCK is a cube of side 100, using 12 triangular faces.

• block100.stla, the ASCII STL file;
• block100.png, a PNG image of the shape;

BOTTLE is a bottle using 1240 triangular faces.

• bottle.stla, the ASCII STL file;
• bottle.png, a PNG image of the shape;

CUBE is a bottle using 12 triangular faces.

• cube.stla, the ASCII STL file;
• cube.png, a PNG image of the shape;

FLAT is a flat shape using 3 triangular faces.

• flat.stla, the ASCII STL file;
• flat.png, a PNG image of the shape;

HUMANOID_TRI is a humanoid shape using 96 triangular faces.

• humanoid_tri.stla, the ASCII STL file;
• humanoid_tri.png, a PNG image of the shape;

MAGNOLIA is a magnolia blossom, using 1247 triangular faces and 3741 nodes.

• magnolia.stla, the ASCII STL file;
• magnolia.png, a PNG image of the shape;

SPHERE is a sphere using 228 triangular faces and 684 nodes.

• sphere.stla, the ASCII STL file;
• sphere.png, a PNG image of the shape;

TEAPOT is (half of) a teapot using 2016 triangular faces and 6048 nodes.

• teapot.stla, the ASCII STL file;
• teapot.png, a PNG image of the shape;

TILER_3D is a tiling pattern in 3D created by TILER_3D.

• tiler_3d.stla, the ASCII STL file;
• tiler_3d.png, a PNG image of the shape;

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