An Introduction to Programming with IDL

Transcription

1 An Introduction to Programming with IDL Interactive Data Language Kenneth P. Bowman Department of Atmospheric Sciences Texas A&M University AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Academic Press is an imprint of Elsevier

2 Acquisitions Editor: Jennifer Helé Project Manager: Jeff Freeland Marketing Manager: Linda Beattie Cover Art Direction: Cate Rickard Barr Interior Design: Julio Esperas Composition: CEPHA Imaging Pvt. Ltd. Cover Printer: Phoenix Color Corp. Interior Printer: The Maple-Vail Book Manufacturing Group Academic Press is an imprint of Elsevier 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA 525 B Street, Suite 1900, San Diego, California , USA 84 Theobald s Road, London WC1X 8RR, UK This book is printed on acid-free paper. Copyright 2006, Elsevier Inc. All rights reserved. IDL is a registered trademark of Research Systems, Inc. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permissions may be sought directly from Elsevier s Science & Technology Rights Department in Oxford, UK: phone: (+44) , fax: (+44) , permissions@elsevier.com. You may also complete your request on-line via the Elsevier homepage ( by selecting Support & Contact then Copyright and Permission and then Obtaining Permissions. Library of Congress Cataloging-in-Publication Data Application submitted British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN 13: ISBN 10: X For information on all Elsevier Academic Press Publications visit our Web site at Printed in the United States of America

3 Preface Acknowledgments xi xiii Part I IDL BASICS 1 Chapter 1 Introduction What Is IDL? IDL Resources The IDL Software System 5 Chapter 2 IDL Manuals and Books Features of This Book IDL Documentation from Research Systems Other IDL Books 11 Chapter 3 Interactive IDL IDL Commands Setting Up IDL Starting and Exiting IDL Interrupting and Restarting IDL Calculations Simple IDL Statements Getting Information Variables Arrays Graphics Summary Exercises 31 Chapter 4 IDL Scripts (Batch Jobs) IDL Commands and Notation A Note on Files and File Names Making a Script 34 v

4 vi 4.4 Journaling Summary Exercises 38 Chapter 5 Integer Constants and Variables IDL Commands and Notation Decimal and Binary Notation BYTE Constants and Variables INT Constants and Variables LONG Constants and Variables Other Integer Types Converting One Integer Type to Another Summary Exercises 47 Chapter 6 Floating-Point Constants and Variables IDL Commands and Notation Development of Floating-Point Methods Limitations of Floating-Point Arithmetic Single-Precision Constants and Variables Double-Precision Constants and Variables Type Conversion Rounding Infinities and Not-a-Numbers Summary Exercises 58 Chapter 7 Using Arrays IDL Procedures and Functions Creating Arrays Arithmetic with Arrays Index Arrays Generating a Coordinate Array Changing the Shape of an Array Using Part of an Array Expanding or Shrinking (Rebinning) an Array Reversing an Array Rotating or Transposing an Array Shifting an Array Summary Exercises 75

5 vii Chapter 8 Searching and Sorting IDL Procedures and Functions Finding Values in an Array That Satisfy a Logical Condition Sorting an Array Finding a Value in a Sorted Array Summary Exercises 82 Chapter 9 Structures IDL Commands and Keywords Named Structures Anonymous Structures Hierarchical Structures Additional Topics Summary Exercises 90 Part II INPUT AND OUTPUT 91 Chapter 10 Printing Text IDL Commands and Keywords Free-Format Output Formatted Output Printing a Table Output to Files Summary Exercises 100 Chapter 11 Reading Text IDL Commands and Keywords Reading Text from the Terminal Reading Text from Files Summary Exercises 105 Chapter 12 Writing and Reading Binary Files IDL Commands and Keywords Writing Binary Files Reading Binary Files Exchanging Files with Fortran Programs Summary Exercises 114

6 viii Chapter 13 Reading NetCDF Files IDL Procedures and Functions NetCDF Basics Reading Attributes A Real Data File Summary Exercises 124 Chapter 14 Writing NetCDF Files IDL Procedures and Functions Writing a NetCDF File Writing Parts of an Array Summary Exercises 133 Part III PROGRAM STRUCTURE AND CONTROL 135 Chapter 15 Procedures and Functions IDL Commands and Keywords Built-in Procedures and Functions Writing Procedures Writing Functions Keyword Parameters Optional Parameters Summary Exercises 150 Chapter 16 Program Control IDL Commands and Keywords BEGIN...END Statements IF...THEN...ELSE Statements FOR Loops WHILE Loops Other Control Structures Summary 157 Part IV GRAPHICS 159 Chapter 17 Line Graphs IDL Commands for Plotting Line Graphs Plotting Styles Titles and Labels Axes 167

7 ix 17.5 Multiple Plots Per Page Summary 170 Chapter 18 Contour and Surface Plots IDL Commands and Keywords Contour Plots Surface Plots Shaded Surface Plots Summary 179 Chapter 19 Mapping IDL Commands and Keywords Drawing Maps Contour Plots on Maps Other Plots on Maps Summary 191 Chapter 20 Printing Graphics IDL Commands and Keywords Device Drivers The PostScript Device The PRINTER Device Some Limitations of the PRINTER and PS Devices Summary Exercises 200 Chapter 21 Color and Image Display IDL Commands and Keywords Color Basics Bit Devices Bit Devices Printing Color Output Summary 217 Chapter 22 Animation IDL Commands and Keywords Background Using XINTERANIMATE Summary Exercises 224

8 x Part V APPLICATIONS 225 Chapter 23 Statistics and Pseudorandom Numbers IDL Commands and Keywords Pseudorandom Numbers Basic Statistics Regression and Correlation Curve Fitting Significance Tests Summary 235 Chapter 24 Interpolation IDL Commands and Keywords Background D Interpolation Bilinear Interpolation Higher Dimensions Irregular Grids Summary 246 Chapter 25 Fourier Analysis IDL Commands and Keywords Background The IDL FFT Fourier Filtering Summary Exercises 262 Appendix A An IDL Style Guide 263 A.1 IDL Style Rules 263 A.2 Examples of Good and Bad Style 266 A.3 IDL Reserved Words 269 Appendix B Example Procedures, Functions, Scripts, and Data Files 271 B.1 Example Procedures, Functions, Scripts 271 B.2 Data Files 275 Bibliography 277 Index 279