NCL > Application examples > Basic examples

ContourPlot example 10

Refining a contour plot

This example demonstrates how to use HLUs and NCL to read data from a netCDF file and create a series of contour plots from the data. The names of the example codes that create this plot are cn10c.c, cn10f.f, and cn10n.ncl.

Discussion

This module discusses how to create this plot using HLU function calls and NCL. This module also shows how to read netCDF data from a file and produce a series of contour plots. The example demonstrates how to create a contour plot using mostly defaults, how to turn on contour fill and other plot attributes, how to plot a sub-area, how to create an XyPlot through the contoured area, and how to overlay the contour plot on a MapPlot object. There is no resource file for this example, as all the resources are set in the source code.

A detailed discussion of how this example works appears in its source code.

Creating the plot using HLU C library calls

The HLU C program that generates this plot is called cn10c.c.

Creating the plot using HLU FORTRAN library calls

The HLU FORTRAN program that generates this plot is called cn10f.f.

Creating the plot using NCL

The NCL script that generates this plot is called cn10n.ncl.

The data

The data for this plot is from a netCDF file called cn10n.cdf.

The data file is located in your NCAR Graphics data directory in a subdirectory called "cdf". You can get the name of the data directory by typing "ncargpath data" at your shell prompt. If you have netCDF installed on your system, then you can change directory to where the netCDF file resides and type "ncdump -h cn10n.cdf" to view the header information for this data file.

How to run this example

The examples are installed in the following locations:

  • $NCARG_ROOT/lib/ncarg/hluex/contourplot/cn10c.c
  • $NCARG_ROOT/lib/ncarg/hluex/contourplot/cn10f.f
  • $NCARG_ROOT/lib/ncarg/nclex/contourplot/cn10n.ncl
The netCDF data file is installed in the following location:

  • $NCARG_ROOT/lib/ncarg/data/cdf/cn10n.cdf
You can copy this example and run it by typing "ng4ex cn10c", "ng4ex cn10f", or "ng4ex cn10n". A copy of the source file and resource file will be placed in your current working directory. The source code will be compiled and automatically run for you. You must have the netCDF library installed on your system in order to compile the C or FORTRAN version of this example.

You can view the output NCGM file using the NCAR Graphics ctrans utility. (Type "ctrans cn10n.ncgm".)