A concern commonly raised during discussions around electronic navigation systems is the way that they can contribute toward incidents. The scenarios usually revolve around lack of training and an over reliance on the computer software. In fact several grounding incidents have been directly attributed to this. In each case the ECDIS was not correctly set up for the conditions, presumably because it was not well understood. At the same time other more traditional approaches to navigation such as looking out of the window were being neglected. The inevitable result is a lot of unhappiness.

So what is really going on here? How come a system which is designed to make navigation safer is causing problems instead?

First off, we should probably assert that electronic chart systems are, for the most part, a big benefit. Very basic properties such as accuracy of positioning and ease of chart updating set such systems head and shoulders above paper charts. I can go on with a long list but you probably already know it. So where is the downside? At CherSoft, there are two issues that we are very aware of: first up the screen is not as big or clear as a paper chart, secondly the user interface can act as a barrier. Good software should be mitigating these issues by making optimal use of the screen real estate and by being easy to use. Obviously, if the software is easy to use then training is less of an issue.

But there is another angle to this.

A long time ago when Microsoft Word was a DOS application I was asked about how to set up the page layout. I had never looked at this at all before but I gave it a go and it only took a few minutes to get sorted. The secretary was impressed with my knowledge of Word. Of course I was actually making it up as I was going along but the results were fine so that didn’t matter. I’d never had any training on Word and I did not have a detailed knowledge of its settings. That was not so important because I did know the principles behind it and understood the general approach of the User Interface. My knowledge was to do with the domain rather than the details.

Understanding navigation systems is the core issue. Many systems, particularly the professional, type approved ones, are devilishly difficult to use. This may surprise you. Certainly if you had paid several thousands for a state of the art system then you might hope it would be quite approachable. The trouble is that not only are the User Interfaces, for the most part, quite primitive, but also the mechanisms around obtaining and updating charts tend to be complex. The latter is mostly associated with the dragon of Digital Rights Management. These factors mean that training, of necessity, has to be concerned with a lot of detail.

We think that the navigation system should be easy to use. It should be sufficiently easy to use that someone with knowledge of navigation and some elementary computer skills should be able to use it. I am not going to claim that Nuno™ achieves this yet, but it is what we are aiming for. This still leaves a gap though. It still leaves space for the fatal over-reliance on computers. Perhaps this is more of a cultural thing than a specific training issue. I suspect that the more you know about computers and their weaknesses then the less likely you are to drop unsuitable responsibility on one. Another way of looking at this is to consider that a computer, however clever it appears, is just a tool.

I think there needs to be convergence. The electronic tools should be useful without demanding specific knowledge. At the same time the limits of the tool should be understood at a domain level rather than in terms of the detail. My hope would be that the increasingly computer savvy people driving the ship will be using these tools so that they can spend more time looking out of the window rather than less.

I was quietly browsing the internet the other day and came across a website which offered me a ‘cracked’ version of Nuno Navigator. This struck me as interesting so I promptly downloaded a copy and got the team here to have a look at it. I was actually quite intrigued to know how it had been cracked. In some ways I was quite flattered. Nuno does not really cost very much but someone had still gone to the the trouble of hacking it.

While the file was being examined I went off to see if I could find other free downloads of cracked versions of Nuno. Turned up a couple more. Now these all came off sites that were offering an awful lot of software by way of free downloads. In fact there appeared to be most of the applications that we more usually pay for. Someone has been doing an awful lot of hacking license enforcement systems.

First result back from the labs was that the certificate on what claimed to be the Nuno installer had changed. This is pretty easy to check for yourself. Right click on the file and then select properties. On the tab labeled ‘Digital Signatures’ you should see that the file has been signed by CherSoft. These signatures are pretty reliable. If it does not say CherSoft then it has not come for us.

The particular file we were looking at what signed with the name ‘Softdeluxe’. I have no idea who this is. We are not entirely sure what the file does either. It contains a couple of GUIDs which pop up in malware reports. It also contains a link to the Nuno download page. Best bet was that it would install something that you would probably rather not have on your computer and then take you to our website or even just download the genuine Nuno installer.

The next one we found was even more exciting. This was signed by ‘EliteCom LLC’ and appeared to be a disguised installer for Filehunter-win32.exe which very much looks like malware – a Trojan of some sort. There are many warnings on the ‘net about this one.

We checked a couple more ‘free’ downloads and concluded that no-one had hacked Nuno but that there was quite a bit of social engineering going on. The main theme appears to be one of tempting you with a free/hacked/cracked download. By the time you discover you are not getting what you hoped for it has installed something malicious. They are not even picking on Nuno especially – pretty much any current software is getting the treatment.

So anyhow, if you want to download Nuno then come to our website. If you have any doubts about what you have downloaded then check the digital signature. This is what they are for.

Imagine your computer just crashed. Maybe you don’t need to stretch your imagination too far for that. They crash, they run out of battery, they get unplugged and sometimes they are simply switched off. The thing is, in this imaginary scenario, that you need Nuno back up and monitoring the route you are still trying to follow. No problem. Start Nuno. It comes back up just as you last saw it and everyone can get back to what they were supposed to be doing in the first place.

Ahem. Did you see what just happened then? Nuno went back to work like it is supposed to. Maybe I should mention what didn’t happen. You didn’t have to reconfigure the GPS connection. You did not need to reload charts, open a file, recover your route, change a setting or anything. It just worked. Whenever something is changed in Nuno it gets written to the hard disc. Sounds simple but many computer programs don’t do this. Instead you get questions like ‘Do you want to save your file?’. With Nuno we figured that being able to restart easily was a really useful feature so we built it in right from the start.

Restartablilty (I may be making up words here) is a big reason for needed multi-level undo and redo. This is a lot less simple. Well, it is simple to use but a real bitch to write the code for. Thing is, without the document style ‘file’ and ‘save’ if you accidentally delete all your work then it is gone forever. And that is not a very friendly thing for a program to do. So instead we implemented the ability to ‘undo’ your last change, or the one before that, or any change since you started Nuno. You can also ‘redo’ any changes that you undid.

 

For even more restartability you can get Nuno to start as soon as you power up your computer.

This method is the same for XP, Vista and Windows 7

First get a copy of the Nuno Navigator shortcut:

• Click on the ‘Start’ button
• Click on ‘All Programs’
• In the list which appears scroll to ‘Nuno Navigator’, left click to expand
• Select ‘Nuno™ Navigator 2011’, right click, choose ‘copy’.

Then open up your Startup folder. This is where you put shortcuts for any application you want to start up as you log on:

• Click on the ‘Start’ button
• Click on ‘All Programs’
• In the list which appears scroll to Startup, right click and click on ‘Explore’.

In the Explorer window you have just opened , right click and choose ‘paste’.

The Nuno™ Navigator 2011 shortcut should now appear in the Startup folder. It will start automatically when you log on.

 

• Where’s that darn moon?
• Am I in danger from lycanthropes?
• If I go down on one knee will she be able to see the romantic moon behind me?
• If this only happens once in a blue moon then when will it happen again?

 

 

 

The answers to these and many other lunar questions can be in the palm of your hand with the Moon application from CherSoft. This is a Windows Phone Application which we have just launched.

We’ve had fun building this application. The core code is the same astronomical algorithms as used in Nuno™. With these we can calculate the relative positions of the earth, the sun and the moon. And with that we can calculated what the moon will look like, when sunrise will be and a bunch of other useful things. The algorithms are based on the work of Jean Meeus, a Belgian Astronomer specializing in celestial mechanics. In particular his book ‘Astronomical Algorithms’, first published in 1991, was a great guide to getting the code right.

First problem was that the code is in C++ and we really needed C# for the Windows Phone. It may be possible to use C++ on a phone but it did not seem a natural fit so we decided to bite the bullet and port it into C#. This actually proved to be reasonably painless. C++ and C# are really quite similar. Not so close that we could do a mechanical translation but not so far that we couldn’t use the same basic approach and organization.

The way to create User Interfaces on a Windows Phone is with XAML. As you can probably guess this is a type of XML. That is just a mechanism. The import concept is that the visual aspects can be developed almost independently of the underlying code. It is really quite clever, and powerful, and fast. We found we could really concentrate a lot more on getting the appearance just right without having to spend a lot of time messing with code. Of course being programmers we did mess with the code if only to see what was going on. But not as much as we usually do.

 

End result is our shiny new application, cunning titled ‘Moon’ and available in the Windows App Store right now. Moon application can tell you exactly where the moon is:

• Altitude, Azimuth, Distance, Illumination
• Next phases
• Rise and Set times

 

 

 

This is one end result. Another is that we have been looking at ways that we can use some of this stuff in Nuno™. First off we could have a phone app associated with Nuno™. What would this do? I am not sure. The screen is a bit small for viewing charts but that is a possibility. How about an app which would act as a route monitor? It would warn you of the next approaching waypoint and tell you about the course to steer. What would you want on a phone?

Yet another end result is that we may start using XAML in Nuno™. You might not actually be able to spot this but watch out for some niftier bits of UI and controls. In the meantime go and check out the Moon app. It only costs $0.99, it has a trial mode if you don’t want to pay anything and it does Blue Moons.

In many ways the single most debilitating factor of an electronic chart display system is the limited screen real estate. You can never really see the whole chart so instead you have a keyhole view. Like looking at a room through the keyhole you can only ever see a part of it. To understand what the room is really like you need to keep looking around and build up a mental picture to supplement the limited bit you can actually see. In all other ways an electronic chart is probably better than a paper one. Updating is quicker and more accurate, so it positioning, laying off courses and the rest of it. Ah, thinking about it, you can operate a paper chart by candlelight so maybe that is the other plus for the paper chart.

With Nuno we have done a bunch of things to try and compensate for the lack of screen size. To begin with we try and avoid dislocating affordances. An affordance is something which by its appearance invites you to do something with it. Like a door handle or in the computer world a button on the screen. It is a very important principle in User Interface design. When you look at a computer program and you want to make it do something the first thing you will do is look for affordances – something you can press, drag, select or whatever. A dislocating affordance is one which suddenly makes the whole screen change, like a control which make the chart view jump. It is a bit like spying through the keyhole, closing your eye, changing position and then looking again. You can see a different bit of the room but you don’t really know how it joins up to the first bit you were looking at. Much better is to maintain a smooth transition from one view to the other using panning and zooming to maintain a sense of continuity.

Overall we have tried to use as much of the screen as possible to display chart. There are no fixed panes that reserve a chunk of the screen. You can arrange a pane like this if you want to but it is not imposed on you. The control bar at the top can be made small and everything else is given over to the chart. Many of the affordances are arranged around the screen in fixed positions so that you will always know where to find them but they become translucent when not being used. Sure they obscure the chart a little bit but you can still see chart and we think the more chart you can see the better.

With vector charts your view is not onto something like a bounded paper chart but more like a view onto an enormous cylinder where the whole world is projected. If you keep panning right you will eventually come back to where you started. This means that however big the screen is that you will still need to pan and zoom. I should clarify at this point that I am not simply talking about the physical dimensions of the screen but also the number of pixels or dots that are used to make the image. To display an image of a paper chart on a screen at about the same size as the original you need about 100 dots per inch (dpi). Less than this and the image will be blurred. More than this and the image will sharped up and be clearer to look at. Traditionally charts are printed with at least 600 dpi so to get a screen image as well defined as that on the  paper is not really possible with current screens. 100 dpi is reasonable a compromise.

So what is the best size for a screen? Well you need to be able to see it all without having to walk around. In fact if you could reach across to any part of it then that would be good. Maybe this problem is already solved. Maybe a paper chart has evolved to be just the right size. Maybe in 200 years of making charts we have actually come up with something that is just the right size for the job. Now the standard size for a full paper chart is a half double elephant. This is not, as you might think, the same as a single elephant. The elephant folio is up to 23 inches tall whereas a double elephant is 50 inches. So the paper chart, at around 25 x 40 inches is in fact a half double elephant.

A screen this size would need to 5,000 pixels wide. At the moment the best mainstream video standard is dual channel DVI which supports up to 2,560 x 1,600. So four of these lashed together could look pretty good. A company called Cinemassive (great name) make a set of monitors like this. EyeVis have some pretty good single screens 64” 4096 by 2160 – not quite enough pixels and a rather eye watering price. However you look at it though we are nearly there.

One problem with such a big screen would be that your poor old mouse is going to run out of steam. You would need a mouse mat four times bigger unless you could manage to move the mouse four times more precisely. But imagine that you had the screen set up just like a chart table – wouldn’t you just want to reach out and touch it? Multi-touch technology is really starting to gain pace now. Once you get to grips with an iPad you soon find it is a great way of doing things (although pretty hopeless if you have gloves on I recently discovered). The Microsoft Surface is one of the pioneers here. And it is already a table. Sadly for now it doesn’t have enough pixels but it is still showing a really good way forward.

So a screen the size of a chart table is not going to suit every vessel but we are close to a practical system. In fact my company are looking at a project to prototype a full sized electronic chart table along these lines. It is quite feasible that screens will progressively get lighter and cheaper and maybe you could even roll it up. Bigger is better?

Lloyd’s List today has heralded a move towards cheaper ECDIS. Most ECDIS are a pretty bog standard PC bolted into a nice case along with some software. It is the software that makes the PC sing and dance. This is what turns an ordinary computer into an ECDIS. This is what the navigator works with and steers his ship by. This is what the training is all about.

How do you reduce the price of software? There is a simple equation in industry that says you cannot sell things for less than the cost of manufacture. Well you can, but not as a long term proposition. In general the idea of any manufacturing business is that you get some raw materials, make something from them and then sell the product so that you can cover your costs and maybe make some profit.

Making cheap software then, how can you cut the costs? There are three broad areas of cost in manufacturing:

• premises, infrastructure and plant
• sales and marketing
• raw materials

Nothing too special about the premises. Any half decent office will do. Infrastructure is the usual raft of management, accountants, office cleaners, human resource experts and other essentials. Plant pretty much comes down to computers and an Internet connections.

Marketing is essential. If nobody knows about you then it can be quite hard to sell.

So far there is nothing unusual, by which I mean that these considerations apply to pretty much any industry to a greater or lesser extent. The way you control costs on this stuff is conventional and well understood.

However when we get to sales things start to get a little more interesting. Cost of sales for software? Just about zero. There was a time when we would put a CD in a pretty box with a thick manual but we’ve just about grown out of this now. Nobody ever read the manual, the box would end up in the bin and having installed the CD you would often find out that the first thing you needed to do was to download an update. So most software is supplied directly these days and that costs nothing, approximately. The server sits there supplying copies of the software and whether is sends out to 10 or 10,000 users really makes little cost difference. In fact really all that business with the boxes and CDs still didn’t add any significant overhead. Low cost of sales means that there are some big bonuses in selling large volumes of licenses. When we talk about selling software we are really talking about selling licenses to use a copy of the software and this is really cheap to do.

The raw materials for software are people. More specifically people’s brains. The rest of the person is needed as support infrastructure. You need good people to write good software. It is not easy. You need good people and you need time. To build a brick wall faster you can put more builders on the job. Put more programmers on a project and it will often backfire. I have not just made this up, the principle was established over 25 years ago.  Employing clever software engineers is expensive. Very expensive. In fact this is where the bulk of your manufacturing costs are. For a typical software house as much as 90% of their total costs will be wages. People really are the raw material in this industry and in terms of quality, you get what you pay for.

So how can we cut costs? The only cost area that will make and significant difference is the programmers.

Option one. Make the programmers more productive. Shouting, threatening and beating is not very effective (I’ve tried). Providing good tools and using modern project management techniques is much better. Even so there is still a limit. These approaches should be part of a modern software company already so there is not much scope for cutting costs here.

Option two. You could try going for cheaper programmers. This does not work very well. Typically you end up with badly designed software which takes twice as long as you hoped to develop. It is difficult to use, looks rubbish, nobody likes it, there are bugs, it crashes and it is very difficult to maintain. None the less this approach is tried from time to time – you may have encountered some of this software.

Option three. Stop development. If the software does its job and there is no real requirement for further features then this is very effective. Your development costs will be massively reduced and with the minimal cost of sales you will be able to ship software at bargain basement prices.

In the ECDIS world option three has got to look very tempting. Making the software better is very expensive and don’t forget that each new release needs to go through a type approval phase. More expense. Is this a good idea? Well with some 50,000 vessels that will need to fit ECDIS only 5% or so actually have it (ECDIS Revolution Conference). At the same time a much larger proportion have some sort of ECS (not to be used for navigation). This suggests that although they like the electronic navigation bit they are not so keen on the actual ECDIS. Why not? Many possible reasons but my point is that the forthcoming legislation is going to force them to buy a piece of kit that they don’t want. So what would you do? Buy the cheapest solution that gets a tick in the box maybe.

It all comes down to price. A global market of 50,000 is not really all that big for a software product that takes many man-years of work to create. It is going to be hard to claw those costs back. The change in the regulations mean that ECDIS will compete on price and very little else. This will effectively freeze ECDIS development. Option three. You have a type approved solution, it ticks the box and the lower the price the more you will sell.

So, just maybe, we are going to arrive in 2018 with a modern vessel using software written in 2008 based on a display standard from 1998. Yep, it’s going to be 20 years out of date. Just think how good the sat nav in your car was 20 years ago.

The Nuno Navigator team are ecstatically pleased to announce the release of Nuno 2.0. This marks the end of the beta trials. Many thanks to all the people that took part.

Nuno has come a long way since we started. This release includes many improvements:

• Track Log. See where you have been, and save useful bits for later.
• Anchoring Mode. See seabed features only when you need them. More.
• Chart Overview. Makes moving around the chart easier, and shows you more information about the charts themselves. More.
• Quick light recognition. Hover over a light on the chart and see a graphical display of its characteristics. More.
• Data Import and Export. Save your tracks, routes and places as GPX data or KML (Google Maps). Load data from lots of sources into Nuno Navigator.

In addition there have been the usual bug fixes and lots of minor improvements which just make Nuno easier to use.

Chart updating is better and faster. A single button click is all you need to keep your charts up to date. In fact you can even set this to automatic and Nuno will download updates whenever they are needed.

 

Position input is better. Nuno will find your GPS automatically and display the ship position, course and speed. Improved filtering means that the display is more accurate and will not jump around.

 

 

You can quickly create a route plan, just a few clicks on the chart, and then follow it using the dedicated route monitor window. This tracks your vessel and displays course information, distances, cross track error and so on.

 

 

 

Did I mention the search bar? It’s pretty good. You can type in a place name and Nuno will display a list of matches and partial matches. Click on one of these and the chart will fly you straight there. You can also type in a position as a lat/lon or even as a range/bearing from the ship.

 

 

 

One of my favorites is the the pencil line. You can attach one end of this to the ship and it will move as the ship moves. Very handy for keeping an eye on the range and bearing to something.

 

 

 

 

 

Nuno is available at the absurdly cheap price of $100 for which you get and indefinite license to use Nuno and a one year subscription (worth $50) to chart updates, Nuno updates, support and other good things. More.

The first full release of Nuno™ is coming soon. Very soon. Within a week even. It has some great new features, some great improvements and some great bug fixes. Ok, so it is not so great that there are bugs to fix but it is important that we fix them. It is impossible to write code without bugs and anyone that says otherwise probably doesn’t write code.

Here’s a run-down of some of the things we’ve improved:

Overview. A small scale pop-out window with data quality and other overview type information on it. This was discussed here.

Anchoring mode. This is a display setting to show a bit more detail on the chart. Useful if you are maneuvering in to tie up but probably a bit too cluttered for regular use. We’ve done a lot of work on trying to manage clutter in chart displays. It is one of the big problems with vector chart systems.

Track log. Nuno will now maintain a record of your vessel track.

So now you can see exactly where you have been. You can save portions of the track in case you need a permanent record.

Chart Updating. This is getting better all the time. Our aim is to make chart updating so simple that you will, with almost no effort, have a complete set of up to date charts all the time. We are also working on reducing the time taken to update charts.

That is just a sample. There are lots of small improvements and features which all go towards making Nuno a better navigation system and better to use. We have lots of improvements in the pipeline as well. Over the next few months we will be adding support for AIS, Active Captain and others.

What features would you like to see? We’d really like to hear from you.

In the meantime the beta program is still running and as an added incentive for anyone who has shied away from trying out the beta so far:-

Anyone who downloads and activates the beta version before we launch the full version will get 50% of the purchase price of the full Nuno.

Details about the costs are here. The bottom line is that it will save you $50. Even I think that is a pretty good deal. Downloading and activating the beta is free. No cost. No obligation. But you need to act soon because this offer is only until the full version of Nuno is launched and like I said – this is going to be soon.

There is a lot of talk about ECDIS training at the moment. In the next few years ECDIS will become mandatory for quite a wide range of commercial vessels. Clearly having this kit on board is of little use if nobody knows how to use it and so the requirement for training is becoming prominent.

The argument assumes that the ECDIS cannot be used adequately without appropriate training. This is probably not a bad assumption because the usability of commercial ECDIS software tends to range from difficult to verging on impossible. This may surprise you. Expensive software doing an important job on what may be a large and very expensive vessel. Surely it should be designed to be easy and straight forward to use? Oddly enough this is often not the case. There are several reasons for this:

· The standards, specifically ISO61174, does not lend itself to useable software. This is the performance specification for ECDIS. It is over ten years old and is very detailed. Naturally it is based on ideas and technologies that were prevalent ten years ago. Ten years is a very long time in the computer world – we are talking pre-Windows 2000. What is more at the time the standard was written there was not much around in terms of marine navigation systems and chart data. So rather than drawing on best practices and experience the standard needed to present a vision of how the committee thought that navigation software was supposed to be. Now I don’t actually know how the committee was chosen but I would guess that there were very few computer usability experts amongst the members. Even if there were then they were faced with an impossible job no matter how good their crystal ball was.

· So designing ECDIS compliant software that is also usable is difficult in the first place but it gets worse. Given a realistic situation of limited budgets and resources the focus of the development effort tends towards compliancy issues. Usability is a secondary issue since unless the ECDIS can be certified as compliant with the standards it cannot be sold as an ECDIS.

· Actually getting the software certified is a time consuming and expensive business. I am talking many months and thousands of dollars here. It is not trivial. Once the software is certified then it cannot really be changed without being re-certified. This situation does not lend itself to the sort of on-going development necessary to make genuinely user friendly software. In fact it does not lend itself to any sort of development at all. One of the more popular ECDIS systems around at the moment is actually based on Windows NT4. Remember that? Yes, an improvement over NT3.51 but still a tad short of sparkling when it comes to usability considerations.

· Ship owners are a tight fisted bunch. They typically they will not spend a penny more than necessary on equipment so as long as it meets the regulations. At which point it is usually the cheapest system will do. I am not saying this is wrong, running a ship is a fantastically expensive business, but it does tend to make for comparisons based on simple cost rather than other factors. A particular company’s software may be easier to use but if it is more expensive than its rivals then it will be hard to sell.

Hopefully you are getting the picture now. In an attempt to make ECDIS ‘correct’ and sufficiently similar between all implementations the international regulatory bodies have completely shot themselves in the foot. They have created an environment where the bulk of the development effort and costs are aimed purely at achieving ECDIS compliance and all other considerations fall by the wayside.

S-100 is the chart data standard intended to replace S-57 at some point in the future. The groups working on this have recognized that a typical ECDIS can be a bit tricky to use. They have also noted that each ECDIS tends to be tricky in a different way so they have come up with a solution called ‘S Mode’. The basic idea is that every ECDIS has a button which will set it into S Mode. In this mode the controls, menu options, settings and so on will be exactly the same irrespective of which company made the ECDIS. This is such a beautifully naïve notion. It says ‘we’re a bit scared of this software so let’s make it all the same’. Of course any company developing ECDIS will implement S Mode and probably stop there. Where is the incentive and budget to do anything more? Where is the competitive edge? It all boils down to cost, how else do you differentiate systems that all look and feel the same? And so we arrive at a dead end which ensures training will always be required.

There is only one way to make software more usable and that it to allow software developers to experiment. They have to try out ideas and find out what works. It is very difficult. In fact it is amazingly difficult but we are making progress. There is still ample scope for improvement but at the same time I feel no need at all for a training course in how to use my iPhone. I doubt that many of the millions of iPhone users do. By comparison my last car, which was a few years old, had an early mobile phone in it (this is back in the days when ‘mobile’ actually meant ‘semi-portable’) and no, I could not actually make the first phone call without consulting the manual. That phone and the ECDIS performance standards come from the same era.

Nuno does not come with any training courses. This is not a declaration of irresponsibility but because we don’t think it needs one. It is not technically an ECDIS but it will do pretty much anything that an ECDIS can do and in most cases it will do it a lot better.

Here are some thoughts from Andy about what happens when we change the display scale.

 

What is the difference between a chart used at 1:1,000,000 and one used at 1:10,000?

The most obvious, for charts of the same size, they cover very different amount of area.

The actual numbers are staggering. Consider a chart drawn at a 10^th of the scale – a length on the ground is displayed ten times shorter. This is ten times less detailed on both axes – one hundredth of the area. An area that was represented on a screen of 1 million pixels (a typical laptop) now has to be represented in only 10,000 pixels! That is a serious reduction. It is just 100 pixels by 100 pixels.

Image at 1:10,000

Image of the same geographic area at 1:100,000

Incidentally, the range of useful scales for marine charts is about 1:2,000 to 1:20,000,000. That is an area ratio a million times greater than the above example.

The less detailed one has to leave a lot out. Otherwise it would be a sea of overlapping symbols.

How do we choose what to leave out?

The cartographer does this.

Traditionally, paper charts at different scales were quite separate. The cartographer drew each one by hand, more or less independently. Before even getting to the point of creating detailed charts, lots of decisions have already been made about which areas to even bother with. The mid oceans are only charted at 1:3,500,000 or worse because it doesn't help the mariner to have more detail. There is nothing to hit. It is 7, 14 or even 28 days to land. The detailed charts were only created for navigationally interesting places, ports, narrow channels, the coast because we don’t want to hit it.

With electronic vector charts, the attraction from the chart producer’s point of view is to have a single database of chart data and publish it at different scales – thus reducing the number of layers of chart that he / she has to maintain. In principle, you might feel that this approach allows you to produce a chart at any scale. This is re-enforced by the ability in many navigation programs to display the chart at any scale. But I don’t think this really works.

For a start, the detailed information required to make detailed charts still only exists for the interesting areas. Without that information, a detailed scale chart doesn’t give you any more information, it is just bigger. This is exactly the same as with town street maps. Once the scale is detailed enough to include all the roads and their names, you don’t gain anything – that bumper sized street guide just uses more paper to display the same information in a more spaced out way.

Continuing with the road atlas theme, we have different types of map for different purposes – from national freeways, through state and county maps to individual town plans.

Navigation charts are just the same. In ENC vector charts we have these navigational purposes

Overview

General

Coastal

Approach

Harbor

Berth

Their purposes are, hopefully, fairly obvious from their names. They have a very commercial ship feel to them though – were does that beautiful cove with a sandbar across the entrance fit into the scheme? – it needs a detailed chart, but isn’t the sort of place that commercial shipping cares about. Well, in US waters, Approach is actually more or less continuous along the coastal strip. Harbor also covers a lot more than just harbors, covering a substantial fraction of the coastal strip. So really the navigational purposes are more like scale bands.

Paper charts are also purposed, though, as they are selected manually, it wasn’t so explicit – you just pulled the relevant ones out of the chart drawer - a passage chart for the middle and a harbor chart for each end.

Now look at an electronic chart display. How do we choose the right chart, the right navigational purpose now?

Well, it is a trick question, because typically, you don’t; the computer decides. It switches between purposes as you zoom in and out. This explains why the display changes by more than you expect for some zoom steps. It has just changed navigational purpose.

It is obvious that this will not always do what you want. The computer does not fundamentally know what your current navigational aim is – so as you sail along the coast, it will tend to display harbor charts for the ports you are merely passing by.

The alternative would be to choose the navigational purpose manually – so you always get what you ask for (which might not be quite the same as want you want, or even what you need).

Now we can explain why we don’t do that.

Assume you have a button for each navigational purpose. Say you press “Approach”. The computer displays Approach ENC only. If you are zoomed in to a scale of 1:2,000, you will see a small part of a very coarse chart. If you are zoomed out to a scale of 1:1,000,000 you will just see a few small areas of mush – chart that is so scrunched up you can’t read the detail it contains – and most of the screen will be blank because approach data only exists for the coastal strip. At some scale in-between, you will see a useful Approach chart.

Assuming that we don’t think that computers suffer when we make them work harder, the computer can do much better than this – it can automatically display the less good navigational purposes underneath the approach chart. And it could indicate where there are areas of a more detailed navigational purpose available.

In practice, indicating the areas where there is more detail does not help much – it is usually obvious from the chart where the coast is – that is where the more detailed purposes will cover. There is little point drawing a more detailed navigational purpose when the scale is such that it will be too scrunched up to be legible. It is better to display a less detailed navigational purpose that is nearer to the display scale. So the computer ignores ENC data that has a much more detailed compilation scale than the current display.

In contrast, it is always worth displaying the less detailed purposes underneath because they will still give some context however un-detailed they are – after all, blank areas of screen give no information at all.

Given these rules, if you press the button for the most detailed navigational purpose, Berthing, the computer can automatically display the best ENC data that is available for the current display scale.

In Nuno we decided that this was want you would want 90% of the time, so the complication of having all those buttons was not worth it. Pressto – an automatic system that almost always does want you want, and on the occasions when ideally, you would prefer something slightly different, it errs on the side of safety, by displaying a slightly more detailed chart.

Navigational purposes are the main reason why the content of the chart changes at certain scales. As you zoom in to a scale where it is worth displaying a more detailed navigational purpose, the chart is completely replaced by the new navigational purpose; it might be from a different survey; certainly the person who compiled the chart will have included more detail, both in objects such as buoys and in the wigglyness of the coast and depth contours.

For what it is worth, here are the scales of each navigational purpose…

Nav Purpose	Normal scale range	Outliers
Overview	1:1,100,000 to 1:4,860,000	1:10,000,000
General	1:500,000 to 1:1,200,000	1:1,444,000
Coastal	1:180,000 to 1:600,000
Approach	1:80,000 to 1:120,000	1:52,150
Harbor	1:10,000 to 1:50,000	1:72,000 A few at 1:5,000
Berth (only 2 cells)	1:2,500

Because there is such a wide range of scale within each navigational purpose, it is possible to find an area and scale combination where some of the chart is displayed at one navigational purpose and the rest at the next one. This results in a discontinuity in the chart at the boundary because of the different surveys and detail level in the two purposes.

To summarize this discussion. The software tries to display the best detail available for the current scale. Knowing about the mechanisms involved in the choosing the data to display allows you to understand the discontinuities that sometimes appear and make the best use of the electronic chart.