HOW TO READ A NAUTICAL CHART 2E: A Complete Guide to Understanding and Using Electronic and Paper Charts - Softcover

Calder

Softcover

ISBN 10: 0071779825 ISBN 13: 9780071779821

Verlag: McGraw-Hill Education Ltd, 2012

Inhaltsangabe

Authoritative, practical, and hands-on information on reading and relying on electronic and paper nautical charts

The classic How to Read a Nautical Chart explains every aspect of electronic and paper nautical charts: how a chart is assembled, how to gauge the accuracy of chart data, how to read charts created by other governments, how to use information such as scale, projection technique and datum that every chart contains; how not to get fooled or run aground by overzooming. Nigel Calder teaches you how to squeeze every ounce of information out of a nautical chart (on your GPS, chartplotter, or nav station) and understand the limits of accuracy for all charts, paper and electronic, raster and vector.

This much-awaited second edition addresses the changes in the world of electronic charting, integrated onboard navigation systems, as well as radar overlays and AIS and their interfacing with charts. A new chapter onthe Wiki Revolution explores the mechanisms allowing you to incorporate user-generated content into navigational products and share this content with others-harnessing a user-base never before possible. Calder also explores how 3D-technology and real-time depth and weather information is creating interactive charting capacities that are fundamentally changing how we navigate. Calder's unique, practical insights will help you to navigate safely for years to come.

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Über die Autorin bzw. den Autor

Niger Calder is the author of Marine Diesel Engines (1987, 1991) and Boatowner's Mechanical and Electrical Manual (1989, 1995), the success of which has made him the most sought-after marine how-to writer in the U.S. and U.K. He has published more than 800 magazine articles in SAIL, Cruising World, Ocean Navigator, Yachting World, etc., and lectures on cruising to sell-out crowds. He is also the author of The Cruising Guide to The Northwest Caribbean (IM, 1991) and Cuba: A Cruising Guide (Imray, 1996). He will be testing his newest ideas with his family during a six-month cruise to the Caribbean and South America this winter.

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HOW TO READ A NAUTICAL CHART

A Complete Guide to Using and Understanding Electronic and Paper Charts

By Nigel Calder

The McGraw-Hill Companies, Inc.

Copyright © 2012 Nigel Calder
All rights reserved.

ISBN: 978-0-07-177982-1

Contents

Acknowledgments and Art Credits
Introduction
PART 1. THE LIMITS OF ACCURACY
Chapter 1. Fundamental Chart-Making Concepts
Chapter 2. Horizontal Chart Accuracy
Chapter 3. Vertical Chart Accuracy
Chapter 4. Regulations and Revolution
PART 2. SYMBOLOGY
Chapter 5. Introduction to INT-1
Chapter 6. Topography
Chapter 7. Hydrography
Chapter 8. Aids and Services
PART 3. APPENDIX
Index to INT-1
Glossary and Acronyms
Common Chart Abbreviations
Bibliography
General Index

Excerpt

CHAPTER 1

Fundamental Chart-Making Concepts

UNTIL RECENTLY, there has been little need for chart users to understand thetechnology of chart-making, particularly its limitations, because the tools usedby navigators to determine the position of their vessels were inherently lessaccurate than those used to conduct and display the surveys on which charts arebased. Realizing the limits of accuracy of their tools, navigators tended to bea cautious crowd, giving hazards a wide berth and typically taking proactivemeasures to build in an extra margin of safety for errors and unforeseen events.

Knowing this, and knowing that navigation in inshore waters was by reference tolandmasses and not astronomical fixes, surveyors were more concerned withdepicting an accurate relationship of soundings and hydrographic featuresrelative to the local landmass (coastline) than they were with absolute accuracyrelative to latitude and longitude. The surveyor's maxim was that it is muchmore important to determine an accurate least depth over a shoal or danger thanto determine its geographical position with certainty. Similarly, thecartographer, when showing an area containing many dangers (such as a rockyoutcrop), paid more attention to bringing the area to the attention of thenavigator, so it could be avoided by a good margin, than to accurately showingevery individual rock in its correct position.

All this changed with the advent of satellite-based navigationsystems—notably the global positioning system (GPS). Now a boat's position(latitude and longitude) can be fixed with near-pinpoint accuracy and, in thecase of electronic navigation, accurately displayed on a chart in real time.This encourages many navigators (myself included) to "cut corners" more closelythan they would have done in the past. With such an attitude, it is essentialfor the navigator to grasp both the accuracy with which a fix can be plotted(whether manually or electronically) and the limit of accuracy of the chartitself—together they determine the extent to which it is possible to cutcorners in safety.

The next chapter discusses factors that affect the limits of chart accuracy.However, I first want to explore the extent to which electronic navigationdevices actually give us the plotting accuracy we believe they do. This is bestdone by understanding the basic concepts of mapmaking and chart-making.

A Little History

As early as the third century b.c., Erastothenes and other Greeks establishedthat the world is a sphere, created the concepts of latitude and longitude, anddeveloped basic mapmaking skills. It was not until the sixteenth century a.d.that there were any advances in mapmaking techniques, which occurred largely asa result of steady improvements in the equipment and methods used for makingprecise astronomical observations and for measuring distances and changes inelevation on the ground. From this time, instruments were available formeasuring angles with great accuracy.

The core surveying methodology that developed is noteworthy because it remainedessentially unchanged until recent decades—for both cartographic andinshore hydrographic surveys—and is the basis of many of the charts westill use. A survey started from a single point whose latitude and longitudewere established by astronomical observations. For accurate surveys, theseobservations required heavy, bulky, and expensive equipment, as well as multipleobservations by highly trained observers over a considerable period of time.From the starting point, a long baseline was precisely measured using carefullycalibrated wooden or metal rods or chains. The surveyors measured all changes invertical elevation in order to be able to discount the effects of them on thehorizontal distances covered. In this way, a precise log of horizontal distanceswas maintained, resulting in baseline measurements that were accurate toinches—sometimes over a distance of many miles. The process was slow andpainstaking, and often took years to complete.

Once a baseline had been established, angular measurements were taken from bothends to a third position. Knowing the length of the baseline and the two angles,spherical trigonometry established the distances to the third point withouthaving to make field measurements. The sides of the triangle thus establishedwere now used as fresh baselines to extend the survey, again without having tomake actual distance measurements in the field. The measured baselines plus theprocess of triangulation provided the horizontal distances on the ground. Withone or more precise astronomical observations at a different point to theoriginal one, it was possible to mathematically establish a latitude andlongitude framework and apply it to the results of the survey—there was noneed to obtain astronomical fixes for all the intermediate points, therebyavoiding the time, expense, and difficulties involved.

By the seventeenth century, it was possible to make sufficiently accurateastronomical observations and distance measurements to discover that in one partof the world a degree of latitude as measured astronomically (i.e., withreference to the stars) does not cover the same distance on the ground as itdoes in another part of the world. This would be impossible if the world were aperfect sphere.

From Sphere to Ellipsoid

How to model this nonspherical world? This was more than an academic question.To make maps, national surveyors now universally used an astronomicallydetermined starting point and a measured baseline, working away from thebeginning point by the process of triangulation (see art page 13).

As the surveyors progressed farther afield, if the mapped latitudes andlongitudes were to be kept in sync with the occasional astronomical observations(i.e., real-life latitudes and longitudes), there had to be a model showing therelationship between the distance on the ground and latitude and longitude, andindicating how this relationship changed as the surveyors moved away from theirastronomically determined starting point. This model had to be such that withavailable trigonometrical and computational methods, the mapmakers could adjusttheir data to accurately calculate changing latitudes and longitudes oversubstantial distances—in other words, the model had to be mathematicallypredictable.

The model that was adopted, and...

Details zur Ausgabe

• Verlag: McGraw-Hill Education Ltd
• Erscheinungsdatum: 2012
• Sprache: Englisch
• ISBN 10: 0071779825
• ISBN 13: 9780071779821
• Einband: Taschenbuch
• Auflage: 2
• Anzahl der Seiten: 274
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: gpsr@libri.de; gpsr@libri.de; ; Europaallee 1; Bad Hersfeld; 36244; Deutschland