New users

Introduction

This is the place to start if you are new to PyNGL and PyNIO.

PyNGL (pronounced "pingle") is a Python language module used to visualize scientific data, with an emphasis on high quality 2D visualizations. A working knowledge of Python is assumed.

The NumPy extension module is used for array processing; support for Numeric has been phased out. To aid with the transition between Numeric to NumPy, one can use the conversion routines:

  xnumeric = Numeric.asarray(numpy_array)   # needs Numeric 24.2 to work

  xnumpy = numpy.asarray(numeric_array)

PyNIO is a Python module used for reading and writing files in several different data formats, including netCDF, GRIB1, HDF 4, HDFEOS 2, and CCM history files. In version 1.2.0, support was added for GRIB2 and for netCDF 4 classic files. See the documentation on PyNIO for more details.

Graphic output overview

Please browse the image gallery to see the kind of visualizations that PyNGL can produce and how to use PyNIO to read in various data formats.

Output formats are: PostScript, PDF, X11 screen, or NCGM.

Availability

PyNGL, as well as the associated modules PyNIO and NumPy, are all freely available. For PyNGL and PyNIO, see Downloading and installing PyNGL and PyNIO; for NumPy, go to the SourceForge download page.

A brief history

PyNGL and PyNIO provide Python interfaces to most of the graphics and file input/output functionality existing in the NCAR Command Language (NCL). A knowledge of NCL would give you a leg up in using these modules, but they are meant to be independent from NCL and used as a stand-alone suite of Python functions. In a few circumstances where the NCL documentation applies directly to PyNGL and PyNIO and there is no ambiguity, links are made to the NCL documentation from the PyNGL documentation.

PyNGL and PyNIO represent recent developments in the evolution of a package that dates back several decades. Those who are interested can view the genealogical chart.

Getting started

After having read this page, you should go to the Tutorial which presents a sequence of example codes of increasing complexity. For each example, line-by-line comments are provided.

All PyNGL codes have the same basic code structure:

read in data
process the data
specify a graphic output device
specify resources that control plot appearance
call a plotting function

As a new user you will probably find the resource specifications to have the steepest learning curve, since there are well over a thousand of them controlling, for example, whether your tick marks point in or out, how many contour lines you want, what font to use, what color table to use, and so forth. There are three relevant pages relating to resources:

link description
Resources overview A brief introduction describing what resources are and how they are used.
Resource files A discussion of how to set multiple resource values by putting them in files.
Resources documentation Links (ordered alphabetically as well as grouped by resource type) to documentation for all resources.

link	description
Resources overview	A brief introduction describing what resources are and how they are used.
Resource files	A discussion of how to set multiple resource values by putting them in files.
Resources documentation	Links (ordered alphabetically as well as grouped by resource type) to documentation for all resources.

You will have a good start on understanding some of the most common resources after having gone through the tutorial.

Module contents

The links on the sidebar of the PyNGL home page give an overview of what PyNGL is. The following tables summarize where the links on the sidebar will take you. It might help you to click through the links to get a feel for what's there. Clicking on "PyNGL" in the page header for any page will take you back to the home page.

Examples menu

link	description
overview	a description of how to run the examples
gallery	lists all example images with links to the sources
alphabetical	alphabetical list of the examples with brief descriptions
by category	lists example categories with links to images
by function	for a given PyNGL function, lists the examples that use that function
by resource	for a given PyNGL resource name, lists the examples that use that resource
by effect	lists various graphic effects and the examples that illustrate those

Links menu

link	description
What's new	lists the important new things in each version
Tutorial	a sequence of examples with line-by-line explanations
Functions	lists all of the available PyNGL functions
Resources	lists all of the available PyNGL resources
PyNIO	link to the PyNIO documentation
Colors	description of color usage and a gallery of color tables
FAQ	Frequently asked questions
User forum	how to subscribe to the pyngl-talk mailing list
Quick links	Links to various color and pattern tables, etc.
Related URLs	listing of external URLs of interest
Bugs	list of known bugs and instructions on filing a bug report
Glossary	glossary
Download	Instructions on how to download and install PyNGL and PyNIO

Acknowledgements

Authors: Fred Clare, Dave Brown, and Mary Haley

PyNGL and PyNIO use several other publicly-available software packages for some of their file I/O and data analysis routines. Some of these software packages are listed below. If you feel one is missing, please contact Mary Haley.

HDF - a physical file format for storing scientific data.
HDF-EOS - a library that is an extension of HDF, built specifically to handle data from the Earth Observing System (EOS), a suite of satellites launched by NASA.
NCAR Graphics - a library containing over two dozen Fortran and C utilities for drawing publication-quality visualizations like contours, maps, vectors, streamlines, weather maps, surfaces, histograms, X/Y plots, annotations, and more.
Ngmath - a collection of mathematical procedures.
netCDF - a machine-independent format for representing scientific data (also, an interface for array-oriented data access and a library that provides an implementation of the interface).
Triangle - a two-dimensional quality mesh generator and Delaunay triangulator, used in PyNGL's contouring package for non-uniform grids.

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