Summary
There is a wide variety of navigational aids and they are classified according to an international system.Table of Contents
Overview
Background
The full set of navigational aids from the U.S. Coast Guard’s Light List for District 9 is 4669 observations. District 9 is comprised of the Great Lakes and the St. Lawrence River above the St. Regis River. A large portion of the observations contain missing values. The precise percentage of missing values in the “characteristic” variable was
35.19%. The “characteristic” variable is a field that actually has three other variables within it. Each cell contains 3 parts: a description of the kind of light, like “flashing”; a color, very often red or green; and a period of time over which a light cycles, like “4s.” Examples include Fl R 4s, Iso G 6s and Fl (2+1)G 6s.
Abbreviations
The reference manual for the light lists describes the characteristic column as " Light characteristic for lighted aids to navigation."[1] The list also includes abbreviations and definitions for the light list.
Figure 1: Source: U.S. Coast Guard Light List.
Definitions
Alternating- A light showing different colors alternately.
Fixed- A light showing continously and steadily.
Isophase- A light in which all duration of light and darkness are equal.
Flashing- A light in which the total duration of light in a period is shorter than the total duration of darkness and the appearances of light are usually of equal duration.
Morse- A light in which appearances of light of two clearly different durations (dots and dashes) are grouped to represent a character or characters in the Morse code.
Occulting- A light in which the total duration of light in a period is longer than the total duration of darkness and the intervals of darkness are usually of equal duration.
Quick- A light in which flashes are produced at a rate of 60 flashes per minute.
Methodology
The variable characteristic was selected from the full data frame. It was further split into three parts using stringr::str_split(df$characteristic, " ").[2] The resulting list was extracted by element in three parts: light, color and time. The new variables were converted into factor/categorical data using the forcats[3] package. The dataframe then grouped the categorical values together and tallied the number within each group. [4] The treeplot [5] package generated a plot showing the frequency of color, light and time were plotted.
Color
Light
Time
Conclusion
The variable characteristic contains additional important information about navigational aids with lights. When separated, the variables tells the kind of light, its color and the time for the light to cycle. While there are a wide variety of lights, the most common light is Fl R 4s or a flashing red light that flashes every four seconds. 553 lights have that characteristic. The second most common light was Fl G 4s or a flashing green light that flashes every four seconds. 538 lights were described in that way. There were additional ways to overlap the variables in a single treemap;however, it made the diagrams difficult to interpret. Hopefully, review of this post helps others to understand navigational charts and provides a basic understanding of what lights are commonly encountered on the Great Lakes. Be safe!
References
Appendix–Light Characteristics by Group
Disclaimer
The views, analysis and conclusions presented within this paper represent the author’s alone and not of any other person, organization or government entity. While I have made every reasonable effort to ensure that the information in this article was correct, it will nonetheless contain errors, inaccuracies and inconsistencies. It is a working paper subject to revision without notice as additional information becomes available. Any liability is disclaimd as to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from negligence, accident, or any other cause. The author(s) received no financial support for the research, authorship, and/or publication of this article.
Reproducibility
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date 2021-03-10
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