NCL > Application examples > Basic examples

XyPlot example 6

Using multiple lines, external data, and legends

This example can be created using HLU C library calls, HLU FORTRAN library calls, or NCL. This is an advanced example that demonstrates how to create a plot that contains multiple lines on multiple plots with a legend. The names of the source files for this example are xy06c.c, xy06f.f, and xy06n.ncl.


This module discusses how to create this plot using HLU function calls and NCL. A resource file is included with this example, and it is called xy06.res. This file is used to change the default resource settings for the plot.

This example plots temperature, pressure, and wind speed for various cities each hour on 3/18/95. Missing values are represented by a break in the line. The resource "xyExplicitLegendLabels" is used to indicate which cities we want to plot the data for.

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

Creating the plot using HLUs

The HLU C program that generates this plot is called xy06c.c.

Creating the plot using HLU FORTRAN library calls

The HLU FORTRAN program that generates this plot is called xy06f.f.

Creating the plot using NCL

The NCL script that generates this plot is called xy06n.ncl.

The data

The data for this plot were read from netCDF files called "950318nn_sao.cdf", where nn represents the hour the data were taken (00-23).

The data files are 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 files reside and type "ncdump -h 950318nn_sao.cdf" to view the header information for this data file.

How to run this example

You can produce this example by using a C program (xy06c.c), a FORTRAN program (xy06f.f), or an NCL script (xy06n.ncl). The examples are installed in the following locations:

  • $NCARG_ROOT/lib/ncarg/hluex/xyplot/xy06c.c
  • $NCARG_ROOT/lib/ncarg/hluex/xyplot/xy06f.f
  • $NCARG_ROOT/lib/ncarg/nclex/xyplot/xy06n.ncl
The resource file for this example is located in:

  • $NCARG_ROOT/lib/ncarg/resfiles/xyplot/xy06.res
The netCDF data files are installed in the following location:

  • $NCARG_ROOT/lib/ncarg/data/cdf
You can copy this example and run it by typing "ng4ex xy06c", "ng4ex xy06f", or "ng4ex xy06n". 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.