thinking outside the tank

Posts Tagged ‘Google Earth

Crop Duster Animation

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In October 2016 I was contacted by Lem Shattuck, a professional agricultural aviator, who asked me if it would be possible to create an animation in Google Earth of the path followed by a crop-duster aeroplane using GPS data recorded in-flight. The animation would be used in evidence in a trial in which he had been recruited as an expert witness. I was confident that the answer was ‘yes’ but it took several months of exchanging information with Lem to get the results he needed.

The flight in question ended tragically when the plane struck the outer guy of a 1000-foot mast and the pilot lost his life. The details of the case will not be discussed here, rather I want to describe how some software I developed a few years ago, for my own leisure, was adapted to try to clarify what happened and to illustrate how, perhaps, the incident could have been avoided.

There were two principal areas to be addressed:

  1. Create the scene in Google Earth.
  2. Use the animation software to ‘fly’ the model through the scene.

Creating the Google Earth Scene

There were two masts at the site which we called the ‘west tower’ and the ‘east tower’. The plane crashed into the west tower. The 3D Warehouse provided the initial tower model; this had to be modified in SketchUp to make it more realistic. The following series of clickable images shows some of the ways we made the model look closer to what the agricultural pilot sees on a daily basis. Also, one version of the tower was to include high-visibility sleeves and marker balls (Tana markers) on its outer guys.

The modifications included:

  • The original model used rectangular strips to represent the guy wires (figure 1.) and only two of these at each anchor point. The flat guys were replaced with cylinders of the correct diameter, textured to look like weathered steel (figure 2). The number of guys was also increased to four at each anchor.
  • High-visibility sleeves were added by drawing and colouring concentric cylinders (figure 3).
  • Tana markers were added at suitable intervals (figure 4).
  • The anchor points had to be rotated and re-positioned so they coincided with their actual positions at the site (figure 5 and 6). The whole model was scaled and geo-located over multiple iterations to make it as accurate and representative as we could.

A couple of large trees bordered the field and suitable models were placed in the scene (figure 7).

8. M18 aircraft

Lem bought a 3D model of an M18 aircraft, a type commonly used by agricultural pilots and was the aircraft flown on this occasion. I made a few modifications to the model, such as adding the semi-transparent cylinder that simulates propeller rotation. For the animation, the model also had to be oriented so that it would be in straight and level flight and would fly on the heading set by the KML.

Animation software

At the time Lem contacted me I already had some software, written in C#, that was able to animate marine vessels and aeroplanes, as demonstrated by these videos:

Aircraft animations were created from KML input files which included all of the settings that define how an animation should look. One key feature in the specification is the Path, which includes a series of Placemarks, representing the points through which the plane should fly. Settings could be attached at various points in the input  to achive certain effects, such as: identify the model to animate; define the speed at which the model should ‘fly’; determine how much the plane should roll for a given change in heading.

I should point out that flight animations move two objects through Google Earth space. One is the model itself, and the other is the camera that follows the model on its journey.

My software, as it existed at the start of the project, would fit spline curves between the Placemarks in a Path for both the model and the camera (see this video for a demonstration, using javascript, of the cubic spline technique).


Cubic Spline Demonstration

The cubic spline curve fitting creates multiple series of intermediate points that define the flight path of the model, and the location and orientation of the following camera.

Having generated these curves, all that remained would be to create the animation, step by step, by moving the model to successive points, modifying its heading, pitch, and roll at each point. Likewise, the following camera would be advanced to its next location and be rotated about its three axes to point at the model.

Software modifications for the crop duster animation

What Lem was asking me to do was to make an animation using about two-and-a-half minutes of GPS data from a system in common use by agricultural aviators which records a position every two seconds. These data-points were much closer together than I had previously used and would need some tweaking of the interpolation routines.

Another change was to provide two types of view, one to give the pilot’s point of view during the flight, and the other to view the flight from a fixed range and orientation.

Finally, the animations needed to be run using historical imagery which would show the position of the Sun at the time of the incident.


The following links take you to the YouTube videos that acted as backups to the animations that Lem would present in court:

In these videos the LineStrings coloured in yellow represent the GPS data-points while the smoother, white lines, shows the results of the cubic spline interpolation. The red line shows an extrapolation of the GPS data from the last data-point recorded to the known location of the crash.

Low flying in Yosemite Valley

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I am moving all of my Google Earth animations to: Be sure to visit if you’re interested in that kind of thing.

Written by netkingcol

February 18, 2014 at 5:06 pm

Posted in Google Earth

Tagged with , , ,

Madeira – Pearl of the Atlantic

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Pay a visit to the Island of Flowers.

Best viewed at 1080p HD on your largest screen.

Copyright © Colin Hazlehurst, 2014

Written by netkingcol

February 16, 2014 at 7:59 pm

Uluru from the air

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Written by netkingcol

February 12, 2014 at 5:41 pm

Learning to fly the Spirit of St. Louis

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This video shows the results of experiments animating a model aircraft in Google Earth. You can view the content in Google Earth here: LearningToFly.kml

Written by netkingcol

January 6, 2014 at 6:19 pm

Draw a cubic spline curve through Google Earth Placemarks

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Cubic Spline Demonstration

Cubic Spline Demonstration

If you want to draw a spline curve through a set of Placemarks in Google Earth, then this post might help you. I’ve written a script to achieve this (with limitations) and you are welcome to the code which is written in Javascript.

This YouTube video demonstrates the script in action:

You might want to do this, for instance, to create a path for a Camera to follow. I thought at first I would use such a curve to define the flightpath of an animated model aircraft but I realised quite soon that aircraft don’t fly along cubic splines and I needed a different approach to that problem. That’s partly why I’ve only taken the solution this far; I may come back to it later to describe how the camera flies as it follows the aircraft.

It’s not easy or elegant to post code on WordPress so I’m releasing it through Pastebin. At that link you will find an HTML file with embedded Javascript. If you want to try it for yourself you will also need a KML file which has a set of Placemarks in a Folder with id=’PlacemarkFolder’. There is a sample file on Pastebin.

All I’ve done is to bring together bits and pieces from the following resources:

Fragment 1:  initialisation

In this code fragment scripts are imported, variables defined, and Google Earth loaded. Note that in the version displayed here the spline calculations are in a separate file, whereas in the source code on Pastebin I’ve dropped them into the main script; this was purely to reduce the number of file downloads you need to get started.

Two buttons are added to the screen:

  1. A button to fetch a KML file that holds Placemarks. This could be expanded into some sort of file-open dialogue, but I haven’t done that.
  2. A button to run the spline calculation.

Line 29 is the call to create an instance of the Google Earth plugin; it names the <div> element where it should be displayed and identifies the callback function if the plugin is successfully loaded.

Line 34 calls the resize() function to maximise the size of the Earth viewer.


Fragment 2:  resize the screen and initialise the plugin

Line 39 defines the function to resize the Google Earth plugin so it uses most of the available space. A little room is needed beneath the plugin to show the control buttons.

Line 50 defines the callback function which is executed after the plugin is created. The variable ‘gex’ at line 51 becomes an instance of Google Earth Extensions, which is a utility library that the script uses to navigate KML objects.

This is followed by setting up event listeners to monitor the user’s mouse, detecting mousedown, mousemove, and mouseup actions. Together these allow Placemarks to be dragged to new locations. This code was mostly copied from the Google Code Playground, but the code at lines 83 and 84 are extra. The ‘clearLineStrings’ method will remove any existing spline curves from the view, while ‘calculateSpine’ recomputes and redraws the curve based on the new Placemark positions.


Fragment 3:  Fetch a KML file containing Placemarks

Line 93 defines a function to fetch and display a KML file. Line 96 sets the URL of the file. The address shown here will be valid for a while but is not guaranteed so, if you want to play with this code, you will need to copy this file (available on Pastebin), or create your own.

If the file is fetched successfully, the object returned is assigned to global variable ‘designInput’. If there’s a top-level view available, either a <LookAt> or a <Camera>, the plugin viewer navigates to that view using the code at line 106.


Fragment 4:  Extract Placemarks to an array

The ‘getPlacemarks’ function, at line 111, is used to find the Placemarks in the input file and copy them to an array. Line 120 makes a call to function ‘getObjectById’. This function searches the input file for a Folder node with id set to ‘PlacemarkFolder’; this is how the input file happens to be structured; you might have other Placemarks in it but this method only operates on those that you place in the ‘PlacemarkFolder’. You can change this behaviour easily enough.

If the Folder is found, the GE Extensions API is used to find all the Placemarks it contains. Each Placemark is added to array ‘result’ which is returned to the caller.


Fragment 5:  Cubic Spline Part 1

When the KML file has been loaded, you click on the ‘Fit Spline Curve’ button and this action calls the ‘calculateSpline’ function. Line 142 is where ‘getPlacemarks’ is called. If Placemarks were found, the longitude and latitude of each Placemark are extracted and added to their respective arrays (x for longitude and y for latitude). Sorry about the typo at line 144; how unprofessional 🙂

At line 160, Mr. Kuckir’s cubic spline algorithm is called to calculate the required derivatives. It is beyond my ability to describe how this works, so I’m using it as a black box of tricks (see his article for more detail).


Fragment 6:  Cubic Spline Part 2

With the derivatives calculated, it is possible to generate the cubic spline curve. This will be displayed as a KmlLineString, so the first thing to do is to create a Placemark to hold the LineString geometry. Notice that the Placemark is created, at line 163, giving it a unique id which begins with the string ‘SplineCurve’. This makes it easier to remove when the input Placemarks are dragged and we want to show the new curve.

The next step is to iterate through successive pairs of Placemarks. The difference between their longitudes is calculated, and that difference is divided into 100 intermediate points (line 172). For each intermediate longitude, a latitude is calculated using the ‘CubicSpline.interpolate’ function (line 181). This point on the spline curve is added to the LineString with the function call at line 187.

When all pairs of Placemarks have been processed, the resulting curve is displayed by added the LineString Placemark to the plugin’s feature list.


Fragment 7: Supporting functions

  • addToLineString adds the given point to the given LineString.
  • clearLineStrings navigates through the features added to the plugin instance and removes any Placemark that has an id beginning with ‘SplineCurve’.
  • getObjectById searches the features in the plugin for an object with the given id.


Fragment 8: Completing the head element and defining the body element

There is one more function to describe; this is the addButton function which was copied from the Google Code Playground. It provides a way to add command buttons to an HTML page.

Finally, the body of the HTML page is defined. The div with id=’viewKML’ is the place where the Google Earth plugin is displayed.


The script has its limitations and, in many ways, it is a first crude attempt at providing a way to draw spline curves between Placemarks. You will need to take it further if you want something more general purpose. The major limitations are:

  • The spline curve interpolation assumes that longitude is monotonically increasing; it calculates the latitude for a given longitude.
  • The script takes no account of altitude when generating the LineString; all line segments are set to an altitude of 1.0 metres.
  • No way is provided to extract the LineString coordinates.

Don’t forget, if you do download the code, I’ve commented out the URL of the KML input file and I would recommend that you create your own and place it on your own server.

Good luck, and a happy new year.

Copyright © Colin Hazlehurst, 2014

Written by netkingcol

January 2, 2014 at 2:18 pm

Spirit of St Louis departing Roosevelt Field

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A short video introducing Charles Lindbergh’s flight across the Atlantic in the Spirit of St. Louis.

Written by netkingcol

December 16, 2013 at 4:06 pm

Joshua Slocum – Sailing Alone Around the World

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Written by netkingcol

September 16, 2013 at 8:19 pm

Joshua Slocum in Google Earth: Newport to Fairhaven

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Slocum and the Spray have returned to the United States after a voyage of 46,000 miles. However, Slocum feels that the spiritual home of the Spray is at Fairhaven, her place  of birth. Accordingly, less than a week after completing the circumnavigation, he sails his ship to her home port:

The Spray was not quite satisfied till I sailed her around to her birthplace, Fairhaven, Massachusetts, farther along. I had myself a desire to return to the place of the very beginning whence I had, as I have said, renewed my age. So on July 3, with a fair wind, she waltzed beautifully round the coast and up the Acushnet River to Fairhaven, where I secured her to the cedar spile driven in the bank to hold her when she was launched. I could bring her no nearer home.

...where I secured her to the cedar spile driven in the bank to hold her when she was launched. I could bring her no nearer home.

…where I secured her to the cedar spile driven in the bank to hold her when she was launched. I could bring her no nearer home.

There is no other way to mark the end of this journey than in Slocum’s own words:

And now, without having wearied my friends, I hope, with detailed scientific accounts, theories, or deductions, I will only say that I have endeavoured to tell just the story of the adventure itself. This, in my own poor way, having been done, I now moor ship, weather-bitt cables, and leave the sloop Spray, for the present, safe in port.

The section of Joshua Slocum’s journey reported here concludes Chapter XXI of Sailing Alone Around the World and brings Slocum’s adventure to a close.

You can follow the entire voyage in Google Earth at: where three years, two months, and two days of adventure are compressed into five hours and thirty-three minutes of animation and narration.

Effectively, I have created an audio-book from Slocum’s text and added Google Earth illustration. There should be a name such a work.

  • Geobook?
  • kpub (it’s a KML publication)?
  • suggestions are welcomed

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Antigua to Newport

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Slocum sails from Antigua on 05Jun1898. He shapes a course for Cape Hatteras in about 35°N with the intention of coasting along past Chesapeake and Delaware Bays up to New York; a grand finale to the voyage.

The sun passes directly overhead on 08Jun1898 when he is in the latitude of 22° 54’N.

Many think it excessively hot right under the sun. It is not necessarily so. As a matter of fact the thermometer stands at a bearable point whenever there is a breeze and a ripple on the sea, even exactly under the sun. It is often hotter in cities and on sandy shores in higher latitudes.

Several degrees further north Slocum finds the Spray becalmed in the region of the North Atlantic known as the Sargasso Sea. The Sargassum seaweed bunches together into a vast mat around the sloop. For day after day, he can only sit and read and wait for the wind. The smooth and monotonous sea lasts for eight days when a strong south-westerly gale springs up and carries the Spray into the Gulf Stream.

Parts of the sloop’s rigging begin to fail including the peak halyard-block used for controlling the gaff mainsail. More seriously, on 20Jun1898 the jib-stay breaks away at the masthead. This stay is used to carry the jib, but its main function is to hold the mainmast in place. The stay, with the sail attached, falls into the sea but Slocum is able to retrieve it; without the stay the mast sways about ‘like a reed’, but he must climb to the masthead to rig a gun-tackle purchase¹ to secure the mast. He is able to rig a reefed jib to this improvised stay which once again “was soon pulling like a sodger.”

Slocum is now growing weary of the relentless thumping of the waves and the squalls throwing the Spray about. On 23Jun1898 he is pelted by hailstones and subjected to continuous lightning flashes, but there is worse to come; what he calls the climax storm of the voyage:

By slants, however, day and night I worked the sloop in towards the coast, where, on the 25th of June, off Fire Island, she fell into the tornado which, an hour earlier, had swept over New York city with lightning that wrecked buildings and sent trees flying about in splinters; even ships at docks had parted their moorings and smashed into other ships, doing great damage. It was the climax storm of the voyage, but I saw the unmistakable character of it in time to have all snug aboard and receive it under bare poles. Even so, the sloop shivered when it struck her, and she heeled over unwillingly on her beam ends; but rounding to, with a sea-anchor ahead, she righted and faced out the storm.

After the storm, Slocum finds he is closer inshore and, sighting the land, discovers he is some miles to the east of Fire Island. The plan changes; Newport, Rhode Island, is the new destination; he heads eastwards along the coast of Long Island, rounding Montauk Point in the early afternoon. By nightfall, Point Judith is abeam and soon the Beavertail promontory is passed.

The only obstacle now remaining is that the entrance to Newport harbour is mined, owing to the war with Spain. Slocum steers close inshore, hugging the rocks, reasoning that it would be better to have an argument with a rock than with a mine.

Flitting by a low point abreast of the guard-ship, the dear old Dexter, which I knew well, some one on board of her sang out, “There goes a craft!” I threw up a light at once heard the hail, “Spray, ahoy!” It was the voice of a friend, and I knew that a friend would not fire on the Spray. I eased off the main-sheet now, and the Spray swung off for the beacon-lights of the inner harbour. At last she reached port in safety and there, at 1.a.m. on June 27, 1898, cast anchor, after the cruise of more than forty-six thousand miles round the world, during an absence of three years and two months, with two days over for coming up.

The section of Joshua Slocum’s journey reported here opens Chapter XXI of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:


1. A gun-tackle purchase is a simple system of two pulley wheels and a rope.

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Grenada to Antigua

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After a pleasant five-day sojourn, Slocum sails from Grenada on 28May1898, and edges along in the lee of the Antilles.

He still has no chart of the Caribbean, a goat having eaten the only one on board, and decides to call in at Dominica to see if they can spare one. A big advantage of a nautical chart is that it shows the anchoring grounds in and around harbours; Slocum finds that he has anchored the Spray in the zone reserved for quarantined vessels. The officious deputy harbour-master, wanting to exert and demonstrate his power, insists that Slocum moves the Spray to the commercial anchorage. Slocum explains that all he wants is a chart and he’ll be on his way, but the official says he can’t have anything until he moves¹.

After some debate, Slocum slips anchor and heads north for Antigua, arriving at St. John on 01Jun1898.

The section of Joshua Slocum’s journey reported here concludes Chapter XX of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:


1. Once again, Slocum uses language that I have chosen not to repeat. He reports the conversation with the officials on Dominica in the local patois and in a form that would be offensive for me to mimic.

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: St. Roque to Grenada

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Slocum is very sensitive to changes in the feel of the Spray; new sounds, new rhythms, all convey important information to him. On 10May1898, he hears and feels the extra ripples, remembered from earlier voyages, created by the Guiana Current which sweeps around Cape St. Roque and runs at 2 miles per hour along the northern coast of South America all the way to Trinidad. For several days in succession he makes one hundred and eighty miles per day.

War with Spain has broken out. Cuba and the surrounding Caribbean is one of the principal theatres. There were some in Cape Town who warned him:

“The Spaniard will get you! The Spaniard will get you!” To all this I could only say that, even so, he would not get much.

Near the mouth of the Amazon the Spray is overhauled by the warship Oregon. She shows the flags “C B T” which mean: “Are there any men-of-war about?” to which Slocum replies: “No,” and adds for our benefit: “I had not been looking for any.”

The Spray passes Cayenne, the capital of French Guiana, and on the grey morning of 17May1898 he sees the dreary Devil’s Island on the lee bow.

On 18May1898 Slocum sees Polaris, the north star, for the first time in three years as the Spray reaches latitude 7° 13’N.

The island of Tobago bears west by north, distance twenty-two miles on the evening of 20May1898. It’s many years since Slocum has been this way and unknown to him, because his chart of the West Indies was eaten by the goat he had on board from St. Helena to Ascension, there is a new lighthouse at Galera Point on Trinidad. As he sails along the north coast of Tobago he thinks he sees waves breaking on a reef. He throws the sloop offshore but continues to see the white tops of the waves wherever he goes. It seems that no matter which way he steers the reef is all about him. Finally, as the Spray is lifted slightly higher on a wave, the realisation dawns that he is seeing the light from Trinidad playing rhythmically on the waves.

Taking no risks, he tacks back and forth for the rest of the night and then heads out for Grenada, seventy miles to the north-west. He anchors in St. George roads at midnight on 22May1898 and sails into the inner harbour the following morning. The voyage from Cape Town to Grenada has taken forty-two days.

The section of Joshua Slocum’s journey reported here opens Chapter XX of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Ascension to Fernando de Noronha

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Slocum stays on Ascension for three nights¹. He hands over the mail placed in his care at St. Helena and takes lunch with Captain Blaxland, the commander of the island.

On the following day (28Apr1898) he walks to the summit of the island — a peak known as Green Mountain — where a soil profile has developed to the extent that some crops can be grown and rugged pastures support cattle and sheep. A Canadian farmer, Mr. Schank, and his sister are in charge and they give Slocum a tour of the holding.

Rollers crash against the coast making it impossible to take a boat out to the Spray, which is anchored safely in deeper water. Slocum stays in the garrison sharing stories with the officers of the “Stone Frigate R.N.”, the nickname of Ascension Island.

He boards the Spray on the evening of the 29th. Before departure the following day, the sloop is fumigated below decks in an attempt to demonstrate that Slocum is sailing alone. The idea is that nobody could remain concealed below and would have to reveal themselves. With a certificate to affirm that he is the only person on board, Slocum sets sail.

Heading for home, the Spray is on a course that crosses her outbound track of 02Oct1895. On 08May1898 she passes to the south of Fernando de Noronha, an island off the coast of Brazil.

The section of Joshua Slocum’s journey reported here concludes Chapter XIX of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:


1. Either Slocum was a little confused about his dates or the proof-reader of the edition I use didn’t catch this error. The text states first of all: “On the 27th of April the Spray arrived at Ascension…”; the lunch with Captain Blaxland is reported, and the visit to Schank’s farm on Green Mountain is described as taking place “on the following day”; then the text reads: “On the 26th of April, while I was ashore…”  I suspect that this should read: “On the 28th of April,…”  This might seem pedantic, but I need this level of accuracy to make sense of the voyage.

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: St. Helena to Ascension

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After a passage of 1700 miles in 16 days, Slocum arrives at the island of St. Helena on 11Apr1898. He anchors the Spray off Jamestown and goes ashore to pay his respects to the governor, Sir R.A. Sterndale. Once more he is treated well by the dignitaries; in return for two presentations about his voyage he is invited to stay overnight at Plantation House, the governor’s residence up in the hills behind Jamestown; but it’s a double-edged sword — the ‘west room’ where he stays is supposedly haunted and he doesn’t get much sleep:

…the butler, by command of his Excellency, put me up in [the west room]. Indeed, to make sure that no mistake had been made, his Excellency came later to see that I was in the right room, and to tell me all about the ghosts he had seen or heard of. He had discovered all but one, and wishing me pleasant dreams, he hoped I might have the honor of a visit from the unknown one of the west room. For the rest of the chilly night I kept the candle burning, and often looked from under the blankets, thinking that maybe I should meet the great Napoleon face to face; abut I saw only furniture, and the horseshoe that was nailed over the door opposite my bed.

The governor takes Slocum on a tour of the island; on the way back to Jamestown with a fellow American, he visits Longwood, the house in which Napoleon Bonaparte was exiled for the last six years of his life. He died there on 05May1821.

After a lunch at the castle and on receipt of gifts: a large fruit cake from Lady Sterndale, the governor’s wife, and a bag of coffee in the husk from the governor, Slocum sails from St. Helena on 20Apr1898. His companion on the voyage to Ascension is a goat, donated by Clark, an American acquaintance, who claims it would be as friendly as a dog and would bring the benefit of butting the coffee beans out of their pods. Unfortunately, the goat has an appetite for anything and everything edible from grass ropes to Slocum’s straw hat, and his paper chart of the West Indies. Needless to say, the goat is put ashore on arrival at Ascension on 27Apr1898.

The section of Joshua Slocum’s journey reported here introduces Chapter XIX of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:


1. At the time of writing the island of St. Helena does not display as well as it could when using the Google Earth plug-in, regardless of the browser used; the imagery is very low resolution and the terrain detail is absent. Both of these features are displayed correctly in Google Earth itself. Until this problem is resolved, I have provided a button in the contents against this part of the voyage that allows you to download the kml file to Google Earth. If you also have a problem with that option, you can download it at this url: Chapter XIX part 1

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Cape Town to St. Helena

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With the Spray in Alfred dry-dock and a free railway pass in his pocket, Slocum heads inland, making a journey to Kimberley, Johannesburg, and Pretoria. He meets President Krüger, a confirmed believer in the flat-earth hypothesis. Judge Beyers introduces Slocum to Krüger, but makes the mistake of saying he is sailing “round the world”.

“Impossible,” says Krüger angrily; you mean “in the world.”

Slocum checks on the Spray and finds all is well; then he visits Dr. Gill, astronomer royal, at the Cape Observatory. Gill organises a lecture about the voyage which is so well attended that Slocum earns enough money to cover his expenses both during his extended stay in South Africa and the voyage home. In fact Slocum spends three months in South Africa; this is longer than the fastest non-stop solo sailors of today take for the entire voyage.

It’s 26Mar1898 before Slocum is towed out to the offing by the tug Tigre where the spray wallows in a heaving sea without wind for more than a day. It’s a good view:

The light morning breeze, which scantily filled her sails when the tug let go the tow-line, soon died away altogether, and left her riding over a heavy swell, in full view of Table Mountain and the high peaks of the Cape of good Hope. For a while the grand scenery served to relieve the monotony. One of the old circumnavigators (Sir Francis Drake I think), when her first saw this magnificent pile, sang, “‘t is the fairest thing and the grandest cape I’ve seen in the whole circumference of the earth.”

On the second day, the swell shortens; Slocum interprets this, correctly, as meaning that a wind is on the way. He gets under sail and rapidly pulls away from the cape. Once more the pilot of the Pinta is at the helm and Slocum is able to spend long days avidly reading the books he picked up at Cape Town.

Fifteen days later, on 11Apr1898, Slocum is called on deck by the quack of a booby:

Very early that morning I was awakened by that rare bird, the booby, with its harsh quack, which I recognised at once as a call to go on deck; it was as much as to say, “Skipper, there’s land in sight.” I  tumbled out quickly and, sure enough, away ahead in the dim twilight, about twenty miles off, was St. Helena.

The sections of Joshua Slocum’s journey reported here conclude Chapter XVIII of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Port Natal to Cape Town

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Slocum sails from Port Natal [Durban] on 14Dec1897. The passage to Cape Town is about 800 miles. When the Spray is at her best it would take Slocum about one week to cover this distance; however, he expects the weather to be rough even though he has waited and waited for the southern summer to develop. His expectations are met:

On Christmas, 1897, I came to the pitch of the cape. On this day the Spray was trying to stand on her head, and she gave me every reason to believe that she would accomplish the feat before night. she began very early in the morning to pitch and toss about in a most unusual manner¹, and I have to record that, while I was at the end of the bowsprit reefing the jib, she ducked me under water three times for a Christmas box.

A large English steamer passing ran up the signal, “Wishing you a Merry Christmas.” I think the captain was a humorist; his own ship was throwing her propeller out of water.

Two days later the Spray is passing Cape Agulhas, the southernmost point of the African continent, 13 days from Port Natal and with 120 miles still to cover. The winds are more moderate now, but there is still one more gale to come. He shelters in Simons Bay [False Bay] until the wind slackens then he beats the Spray around the Cape of Good Hope, accurately named by early Portuguese navigators as the “Cape of Storms.”

Thirty-five nautical miles later, the Spray runs into calm water in the shelter of Table Mountain. Slocum is in reflective mood; despite sailing alone for so long he anchors in the bay, “clear of the bustle of commerce”, and takes a day to contemplate his achievement of negotiating both Cape Horn and the Cape of Good Hope single-handed.

The next day, he sails the Spray into dry dock where she remains for three months. Slocum does not record the date of his arrival at Cape Town; perhaps it was two or three days after passing Cape Agulhas, which would make it 29Dec or 30Dec1897.

The section of Joshua Slocum’s journey reported here opens Chapter XVIII of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:


1. To simulate pitching and tossing “in a most unusual manner”, I combined animations on all three axes by specifying AnimatedPitch, AnimatedRoll, and AnimatedYaw in the TourMaker Input File for this section of the passage.

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Mauritius to Port Natal

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Fully provisioned and rested, Slocum sails from Port Louis, Mauritius on 26Oct1897. At first the winds are light and he draws away from the island slowly. By the next day he is passing the island of Réunion. The sea is too rough to consider landing, but a pilot comes out of Galets on the north-west corner of the island when Slocum hands over a Mauritius paper.

A course is set to Cape St. Mary, the southernmost point of the island of Madagascar. The trade winds are weakening now and by 30Oct1897 Slocum finds himself becalmed:

The sloop was now drawing near the limits of the trade-wind, and the strong breeze that had carried her with free sheets the many thousands of miles from Sandy Cape, Australia, fell lighter each day until October 30, when it was altogether calm, and a motionless sea held her in a hushed world. I furled the sails at evening, sat down on deck, and enjoyed the vast stillness of the night.

On the following day, a light breeze carries the Spray past Cape St. Mary. About one week later and for the rest of the voyage to Port Natal (Durban) strong gales batter the yacht and heavy thunderstorms were prevalent¹.

Here the Spray suffered as much as she did anywhere, except off Cape Horn. The thunder and lightning preceding this gale were very heavy.

It takes the Spray 18 days to cover the 800 miles between Madagascar and Durban, an average of 45 miles per day made good. This is less than half the distance per day that she is capable of. In reality, the course is not a straight line because the “succession of gales of wind…drove her about in many directions.” So, the Spray is sailing as fast as ever, but on some crazy zig-zag course dictated by the winds².

Slocum stays in Port Natal for four weeks; he meets all the members of both yacht clubs and sails on the crack yacht Florence; he meets Henry Morton Stanley, the Welsh-born naturalised American who is a renowned explorer of Africa; and he encounters a trio of men who believe that the world is flat. They visit Slocum actually expecting to find information that will support their hypothesis. He must disappoint them:

With the advice [to them] to call up some ghost of the dark ages for research, I went ashore, and left these three wise men poring over the Spray‘s track on a chart of the world, which, however, proved nothing to them, for it was on Mercator’s projection, and behold, it was “flat”.

The Spray sails from Port Natal on 14Dec1897 and is once more: “off on her alone,” as they say in Australia.

The section of Joshua Slocum’s journey reported here concludes Chapter XVII of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:


1. Thunder and lightning or rather lightning followed by thunder was a fresh challenge to my animation skills. Again, I used models created in Google SketchUp to represent the effect of lightning; I added to this a couple of thunder tracks from the WavePad sound effect library. Normally I would try to enhance TourMaker by adding a directive that would generate the thunder and lightning automatically. This time I hand-coded it. Each lightning model flashes on and off twice (by setting visibility=1 then visibility=0 ) with each period of visibility lasting about 100ms. A few seconds later the thunder-clap audio is output.

2. I realised that a better animation of a rolling yacht would result from oscillating the angle of roll about the current ‘Roll’ setting, rather than about the vertical. This would create the effect of the yacht being heeled over in the wind while  waves introduce an additional periodic rolling motion. I have amended TourMaker accordingly

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Rodriguez to Mauritius

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Slocum sails from Rodriguez on 16Sep1897 and the Spray covers the 330 nautical miles to Mauritius in a little over three days. Again there is disbelief followed by surprise when it is learnt that he is sailing alone. The port doctor considers he must be well to have sailed so far alone and gives him free pratique – the licence that grants access to a port which certifies that the ship is free of contagious diseases.

Once more there is a keen interest in his voyage; he gives a lecture at the opera house [Port Louis Theatre?] and he meets the local dignitaries including the mayor, the governor, and the American consul.

He stays on the island for a little over 5 weeks — from 19Sep to 26Oct:

At Mauritius, where I drew a long breath, the Spray rested her wings, it being the season of fine weather…It was still winter off stormy Cape of Good Hope, but the storms might whistle there. I determined to see it out in milder Mauritius, visiting Rose Hill, Curipepe [Curepipe], and other places on the island.

He visits the governor’s residence at Reduit and, at the flower conservatory near Moka, a botanist names a newly discovered plant Slocum.

A group of seven young ladies persuade Slocum to take them for a sail “tomorrow”. The problem, he soon remembers, is that he has already agreed to dine with the harbour-master, Captain Wilson on the same day. He hatches a plan to take the women to sea but to make the voyage as rough and uncomfortable as possible so they will want to turn back, allowing him to make his dinner appointment.

The plan backfires:

We sailed almost out of sight of Mauritius, and they just stood up and laughed at seas tumbling aboard, while I was at the helm making the worst weather of it I could…The more the Spray tried to make these young ladies sea-sick, the more they clapped their hands and said: “How lovely it is!” and “How beautifully she skims over the sea!” and “How beautiful our island appears from the distance!” and they still cried “Go on!”

He has to sail over 15 miles out to sea before they are ready to return. The yacht soon reaches the island but Slocum makes the mistake of sailing close inshore towards Port Louis:

…for as we came abreast of Tombo [Tombeau] Bay it enchanted my crew. “Oh, let’s anchor here!” they cried.

Slocum doesn’t get the Spray back to Port Louis until the following day for the young ladies insist on going for a swim in the surf and then sleeping on board overnight. They sleep on deck under a tent of sail.

Next day, Captain Wilson himself appears in the launch to tow them all back to Port Louis.

The section of Joshua Slocum’s journey reported here opens Chapter XVII of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Keeling Cocos to Rodriguez Island

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After five weeks at the Keeling Cocos islands Slocum points the Spray in the direction of Rodriguez Island. On this course the wind and the seas are abeam which makes for an uncomfortable voyage; the yawl rolls unpleasantly and Slocum is drenched when he ventures on deck; yet the Spray holds her course faithfully.

A discrepancy appears between Slocum’s assessment of his position by mental calculation and what the log is telling him. He trails a four-bladed rotator which gives him a measure of the Spray‘s speed through the water. After 15 days the log  differs from his own estimated position by 150 miles. Distrusting the instrument, and knowing his ship well, he “kept an eye lifting for land.”

He notices a stationary patch of cloud beyond the horizon while the clouds of the trade-wind float on their way. He says: “this was a sign of something”; that something, of course, being an island with the cloud forming above its mountains. Sure enough, as he sails on, the dark outline of Rodriguez Island appears ahead.

Hauling in the log, he finds that two of its impeller blades are bent out of shape, probably crushed by a shark; this explains the discrepancy and Slocum’s fine judgement is vindicated once again.

He arrives on the windward side of Rodriguez which is not very welcoming; he hauls around to the leeward side of the island where a pilot comes out to the Spray to guide her through the narrow channel between coral reefs that leads to the inner harbour of Port Mathurin, the village that is the capital of the island.

Slocum has looked forward with relish to this land of plenty and a return to relative civilisation:

For many days I had studied the charts and counted the time of my arrival at this spot, as one might his entrance to the Islands of the Blessed, looking upon it as the terminus of the last long run, made irksome by the want of many things which, from this time on, I could keep well supplied.

On the first evening ashore, in the land of napkins and cut glass, I saw before me still the ghosts of hempen towels and of mugs with handles knocked off. Instead of tossing on the sea, however, as I might have been, here was I in a bright hall, surrounded by sparkling wit, and dining with the governor of the island!

Slocum stays on Rodriguez for eight days, replenishing his supplies with, among other items, sweet potatoes and pomegranates. It’s still too soon to head for the Cape of Good Hope, so the next step of the voyage is the short hop to Mauritius…

The section of Joshua Slocum’s journey reported here concludes Chapter XVI of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:

Copyright © Colin Hazlehurst, 2012

Joshua Slocum in Google Earth: Christmas Island to Keeling Cocos

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It’s 550 miles to the Keeling Cocos island group from Christmas Island. The atoll represents a low-lying target less than ten miles across, so Slocum is aware that careful navigation is required. With his old tin clock that has only a working hour hand this will clearly be a challenge.

Using decades of sailing experience, he reads the future in the sky and in the waves. Seeing high cloud that cuts across the trade-wind pattern, he deduces that a storm is brewing in the direction of the Cape of Good Hope and adjusts his course accordingly to allow for the different combination of wind and current that this brings.

Five days later, his intuition is rewarded when he sights the coconut trees of Keeling Cocos ahead while he is half way up the mast. The relief is so great that he slides down the mast, sits on the deck, and “gives way to his emotions.” He has achieved a remarkable feat and part of it belongs to the Spray‘s ability to hold a course :

I didn’t touch the helm, for with the current and heave of the sea the sloop found herself at the end of the run absolutely in the fairway of the channel. You couldn’t have beaten it in the navy!

Slocum stays on the islands for five weeks; remember he’s allowed himself a leisurely pace so he doesn’t arrive too soon off the Cape of Good Hope. Apart from that, why shouldn’t he linger here? After all: “If there is a paradise on this earth it is Keeling.”

The Spray is hauled ashore for some routine maintenance; then his attempt to haul her afloat fails, and the children of the island are delighted to think that a kpeting (a crab) is holding her down by the keel.

Later, Slocum decides it would be a good idea to ditch a few tons of cement ballast and in its place to carry away some of the giant clams called Tridacna. What isn’t such a good idea is to set off across the bay with one of the locals in:

…a rickety bateau that was fitted with a rotten sail, and this blew away in mid-channel in a squall, that sent us drifting helplessly to sea, where we should have been incontinently lost. With the whole ocean before us to leeward, I was dismayed to see, while we drifted, that there was not a paddle or an oar in the boat! There was an anchor, to be sure, but not enough rope to tie a cat, and we were already in deep water. By great good fortune, however, there was a pole. Plying this as a paddle, with the utmost energy, and by the merest accidental flaw in the wind to favour us, the trap of a boat was worked into shoal water, where we could touch bottom and push her ashore.

After this escape, he presses on with his Tridacna plan but uses a safer boat to gather them.

The section of Joshua Slocum’s journey reported here opens Chapter XVI of Sailing Alone Around the World, and this post is a trailer for the adventure that I am retelling in Google Earth at:

Copyright © Colin Hazlehurst, 2012

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