TRIANGLE_DISPLAY
Plot a Triangulation from TRIANGLE Files

TRIANGLE_DISPLAY is a MATLAB program which plots a triangulation using files associated with the TRIANGLE program.

TRIANGLE_DISPLAY reads the node and element files created by the TRIANGLE program, and displays the information. The user controls how "visible" the nodes and elements are; in particular, nodes can be suppressed, or displayed, or displayed and numbered, and the same is true for elements.

TRIANGLE_DISPLAY is essentially a version of TRIANGULATION_DISPLAY modified to read input files that use the TRIANGLE format.

Jonathan Shewchuk provides a program called showme, which is able to show the same information, and to perform other interesting operations. However, there are at least three reasons why the TRIANGLE_DISPLAY program is useful:

• the user is free to zoom interactively into any part of the mesh displayed by TRIANGLE_DISPLAY;
• the user can save the image (or the portion that has been zoomed) into a wide variety of graphic formats, include JPEG, PNG and TIFF, while showme is restriced to PS and EPS formats; moreover if showme tries to save a snapshot of a large file (such as "greenland"), it can take 20 minutes (after which I gave up) and a huge amount of space. The same image was generated in 20 seconds with this program, and a zoomed image saved to a small 50K file very quickly.
• it is fairly easy to modify the text of TRIANGLE_DISPLAY to better suit the user's needs; in particular, it is easy to read in node-based data and produce contour plots (although I don't have any data to work with yet.)

Usage:

triangle_display ( 'prefix', node_vis, element_vis )

• 'prefix'.node, the node coordinates.
• 'prefix'.ele, the elements

• 0, do not show the nodes;
• 1, show the nodes;
• 2, show the nodes and label them.

• 0, do not show the elements;
• 1, show the elements;
• 2, show the elements and color them.
• 3, show the elements and color them, and label them.

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:

FEM_BASIS_T3_DISPLAY, a MATLAB program which displays a basis function associated with a linear triangle ("T3") mesh.

FEM_BASIS_T6_DISPLAY, a MATLAB program which reads a quadratic triangle mesh and displays any associated basis function.

GRIDLINES, a MATLAB library which gives the user more control over drawing gridlines on a graph than the builtin "grid on" command.

MESH_DISPLAY, a MATLAB program which reads data defining a polygonal mesh and displays it, with optional numbering.

MPAS_GRID_DISPLAY, MATLAB programs which can read an MPAS NETCDF grid file and display the primary polygonal mesh or the dual triangular mesh.

SHOWME, a C program which uses the X Window library to display triangulatons, by Jonathan Shewchuk.

TRI_SURFACE_DISPLAY, a MATLAB program which reads data defining a triangular mesh of a 3D surface and displays it.

TRIANGLE, a C program which computes a triangulation of a geometric region, by Jonathan Shewchuk.

TRIANGLE_FILES, a data directory of examples of files used by the triangle and showme programs.

TRIANGULATION_DISPLAY, a MATLAB program which reads files defining a triangulation and displays an image.

TRIANGULATION_DISPLAY_OPENGL, a C++ program which reads files defining a triangulation and displays an image using Open GL.

TRIANGULATION_PLOT, a MATLAB program which plots a triangulation as a PostScript file.

Reference:

1. Marc deBerg, Marc Krevald, Mark Overmars, Otfried Schwarzkopf,
   Computational Geometry,
   Springer, 2000,
   ISBN: 3-540-65620-0,
   LC: QA448.D38.C65.
2. Joseph ORourke,
   Computational Geometry,
   Second Edition,
   Cambridge, 1998,
   ISBN: 0521649765,
   LC: QA448.D38.

Source Code:

• triangle_display.m the source code.

Examples and Tests:

GREENLAND is a triangulation of Greenland, using a graded (varying-size) mesh of 33,343 nodes and 64,125 nodes. The resulting image is essentially a red blob the shape of Greenland. However, using the ZOOM tool, it is possible to see interesting details of the mesh.

• greenland.node, the nodes;
• greenland.ele, the elements;
• greenland_zoom.png, a zoomed image of the upper right margin of the triangulation.
• greenland.output.txt, the output file.

SQUARE_CIRCLE_HOLE.1 is a square region with a circular hole. 826 nodes and 1517 elements are used.

• square_circle_hole.1.node, the nodes;
• square_circle_hole.1.ele, the elements;
• square_circle_hole.1.png, an image of the triangulation.
• square_circle_hole.1.output.txt, the output file.

You can go up one level to the MATLAB source codes.