# STL Files and 3D Objects Basics

Unyk is a complete tool for preparing any 3D object, it converts files like (PLY, SLC, 3DS, OBJ) to STL format, allowing support structure creation, object repair, edit your design and prepare your build platform.

#### STL FILES

• An STL file consists of a list of triangle data which includes XYZ coordinates of the vertices and a normal that describes the 3D object. One triangle can be called one facet. Basically, by using triangles, it becomes possible to record a 3D object in a 2D space on paper, much as the Mercator maps of the globe are done. Triangles can be reassembled like the curved 3D surfaces. The more triangles contained per square measure (inches or centimeters), the finer the detail and the smoother the surface of the final object will be.

• Each triangle is uniquely defined by its Normal (a line which is perpendicular to the triangle), and three points representing its corners (vertical). Each corner (vertex) is specified by three coordinates. The Normal specifies the inside and outside sides of the triangle.

• The direction of a triangle is defined by the direction of the Normal. The Normal direction is inward and outward if the order of the corner points is counter-clockwise and clockwise respectively (The Right-Hand Rule).

#### OBJECT'S SURFACE

1. 3D object surface is a mesh of triangles. The orientation of a surface is determined by the orientation of all its triangles.
2. The interior and exterior of the object are determined by the orientation of the surface. In the image bellow red and green arrows point outwards to indicate the exterior of the object.

#### OBJECT'S FACES AND POINTS

1. FACES are the number of the triangles which contain the object.
2. POINTS are the number of the corners is contained inside the object
3. EDGES are the sides of a triangle, each triangle has 3 edges that should be shared with others triangles.

#### OBJECT'S SHELLS

1. SHELLS of an object are different parts joining together to make up that object.
2. One SHELL is distinguished from another SHELL by the number of the triangles connected to one EDGE of the triangle. Each EDGE inside a SHELL cannot have more than two connections to any other individual triangle. If an EDGE has more than two connections to other triangles, the triangles will belong to different SHELLS.