TRIANGULATION_ORDER3_CONTOUR
Contour Plots of Triangulated Data

TRIANGULATION_ORDER3_CONTOUR is a MATLAB program which reads datafiles describing a set of nodes, their triangulation, and the value of a scalar quantity at each node, and creates a color contour plot of the scalar.

The program reads three data files:

• a node file, containing X, Y coordinates of points;
• an element file, containing a list of sets of three points making up each triangular element;
• a values file, containing the values of a scalar function U(X,Y) evaluated at each node.

The program automatically displays three plots:

1. An image of the triangulation;
2. A color contour plot with color constant over a triangle.
3. A color contour plot with color linearly interpolated to make a very nice picture.

Usage:

triangulation_order3_contour ( 'prefix' )

• 'prefix'_nodes.txt, lists the node coordinates;
• 'prefix'_elements.txt lists the indices of nodes that form elements.
• 'prefix'_values.txt contains the value assigned to each node.

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 is a data directory which contains a description and examples of the FEM format.

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

FREE_FEM_STOKES is a MATLAB program which is a Stokes flow solver which computes the fluid velocity and pressure in a 2D region. The pressure is a scalar, an order 3 triangulation is used for the pressure, and so it can be plotted by this routine.

TABLE is the format which is used for each of the three input data files.

TRIANGULATION is a MATLAB library which carries out various operations on order 3 ("linear") or order 6 ("quadratic") triangulations.

TRIANGULATION_CORNER, a MATLAB program which patches triangulations so that no triangle has two sides on the boundary.

TRIANGULATION_DELAUNAY_DISCREPANCY is a MATLAB program which measures the amount by which a triangulation fails the local Delaunay test;

TRIANGULATION_HISTOGRAM, a MATLAB program which computes histograms of data over a triangulation.

TRIANGULATION_MASK is a MATLAB program which takes an existing triangulation and deletes triangles and their corresponding nodes as requested by the user.

TRIANGULATION_ORDER3 is a directory which describes the format for the node and element files describing an order 3 triangulation.

TRIANGULATION_ORDER6_CONTOUR is a MATLAB program which can display a contour plot of scalar data defined on a triangulation of order 6.

TRIANGULATION_ORIENT is a MATLAB program which reads data defining a triangulation, makes sure that every triangle has positive orientation, and if not, writes a corrected triangle file.

TRIANGULATION_REFINE is a MATLAB program which reads data defining a triangulation, replaces each triangle by four congruent smaller ones, and writes the new triangulation information to a file.

VECTOR_MAGNITUDE_GRID is a MATLAB program which reads node and vector data from a file, computes an interpolatory function, evaluates on a uniform grid of points specified by the user, and displays a contour plot of the vector magnitude.

Source Code:

• triangulation_order3_contour.m, the routine for creating the contour plot;

Examples and Tests:

CHANNEL is a channel region 3 units wide and 1 unit high. The Stokes flow solver FREE_FEM_STOKES computes the fluid velocity and pressure in the channel. The pressure is a scalar and can be plotted by this routine. Data files you can copy include:

• channel_nodes.txt, a node file;
• channel_elements.txt, an element file;
• channel_values.txt, a value file;
• channel_contours.png, a PNG image of the interpolated contour plot of the data;

ELL is an L-shaped region. Data files you can copy include:

• ell_nodes.txt, a node file;
• ell_elements.txt, an element file;
• ell_values.txt, a value file;
• ell_triangulation.png, a PNG image of the triangulation;
• ell_contours.png, a PNG image of the interpolated contour plot of the data;

LAKE is a simulated lake with an island region. Data files you can copy include:

• lake_nodes.txt, a node file;
• lake_elements.txt, an element file;
• lake_values.txt, a value file;
• lake_triangulation.png, a PNG image of the triangulation;
• lake_contours.png, a PNG image of the interpolated contour plot of the data;

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