POLYGONAL_SURFACE
Two Files Defining a Polygonal Surface

POLYGONAL_SURFACE is a data directory which contains examples of files defining a polygonal surface.

A polygonal surface can be thought of as a surface composed of polygonal faces. The polygons must all be of the same type (triangles, quadrilaterals or whatever).

If the polygons are of higher order than triangles, the user must take care that the vertices of each polygon all lie in a plane. Otherwise, no planar polygon will pass through the vertices. If the nonplanarity is significant, then the display will not look right at all.

The information defining the polygonal surface can be stored in two simple files:

• the node file lists a set of (x,y,z) values, which are vertices of the polygons.
• the element file lists, for each polygonal face, the indices of the nodes that form its vertices. These nodes are generally listed in a "counterclockwise" order, that is, they would be seen as being counterclockwise to an observer from the "outside" or "top" of the surface.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Related Data and Programs:

BEZIER_SURFACE a data directory which describes Bezier surfaces and a file format for storing them.

FEM2D, a data directory which contains examples of 2D FEM files, text files that describe a 2D finite element geometry and associated nodal values;

FEM2D_PACK, a C++ library which contains utilities for 2D finite element calculations.

POLYGONAL_SURFACE_DISPLAY, a MATLAB program which can read in a polygonal surface dataset and display the data.

TRIANGULATION_ORDER3, a data directory which describes the related idea of a linear triangulation in which each triangle is defined by 3 nodes.

TRIANGULATION_ORDER6, a data directory which describes the related idea of a quadratic triangulation in which each triangle is defined by 6 nodes.

Reference:

1. Edward Angel,
   Interactive Computer Graphics, a Top-Down Approach with OpenGL,
   Addison-Wesley, 2000.

Sample Files:

SPHERE_Q4 is a sphere, tiled with an 8 by 8 array of logically rectangular patches. The dataset was created by the sample calling program for FEMPACK and the image is a snapshot of the 3D display created by POLYGONAL_SURFACE_DISPLAY.

• sphere_q4_nodes.txt, the node file;
• sphere_q4_elements.txt, the element file;
• sphere_q4.png, a PNG image of the shape.

SPHERE_T3 is a sphere, tiled with an 8 by 8 array of logically triangular patches. The dataset was created by the sample calling program for FEMPACK and the image is a snapshot of the 3D display created by POLYGONAL_SURFACE_DISPLAY.

• sphere_t3_nodes.txt, the node file;
• sphere_t3_elements.txt, the element file;
• sphere_t3.png, a PNG image of the shape.

TETRA_T6 is a tetrahedron The dataset was created by hand. The image is a snapshot of the 3D display created by POLYGONAL_SURFACE_DISPLAY.

• tetra_t6_nodes.txt, the file of 10 nodes.
• tetra_t6_elements.txt, the element file.
• tetra_t6.png, a PNG image of the shape.

You can go up one level to the DATA page.