Tuesday, September 21, 2021

Role of SCAMIN on ENC

Electronic navigational charts (ENC) are not at all new to navigation. They have been in use by commercial vessels for over 20 years, but they have not really caught on much with recreational mariners. This is in part because they look different from paper charts, but also largely because their presentation on the screen and how users interact with them is so different from the use of raster navigational charts (RNC), which are static images of the paper charts.

One of the things that is notably different with ENC is when you zoom out on the chart, the chart symbols and text labels do not change size. They can do this because ENC are all vector products and they just redraw everything at each new scale, and this keeps the symbols and text  in view

That is, unless you happen to be zooming out on a region that has a lot of symbols. Zoomed in they are far apart on the screen but zoomed out they pile up to the point of becoming totally unreadable.


Above is a sample of a cluttered screen with SCAMIN not engaged. In ENC terminology, this is Display mode All, which means show all objects. This chart is actually over-zoomed in on a very small scale chart.... all new terms we need to look into here. 

There are several ways to clean this up.  


We don't want to go this far, leaving just water and rocks, but there are many levels in between, which we can set up depending on our navigation needs. This is Display mode Base, which is the minimum objects possible.

The ENC and their presentation rules address the issue of cluttered displays by assigning to each charted object an attribute called "Scale minimum," which has an abbreviation SCAMIN.  But to pursue that idea, we need more terminology.

All paper charts have a well-known properly called its chart scale. A scale of 1:40,000, for example, means that 1 inch on the paper chart is equivalent to 40,000 inches (0.55 nmi) on the ground or water being represented. On a 1:80,000 chart, 1 inch would be 80,000 inches, about 1 nmi per inch, and so on. 

That is a plain enough concept, but we can make this more complicated! 

Chart scales are described as large scale or small scale based on thinking of the scale as a fraction: 1/20,000 is a larger number than 1/40,000 which in turn is larger than 1/80,000.  Thus we call 1:10,000 or 1:20,000 large scale charts, whereas 1:80,000 or 1:150,000 are small scale charts. Studying traditional navigation we slowly become used to that, and we could arrange our stack of paper charts in order of increasing or decreasing chart scale as we might choose. 

But any one paper chart only has one scale, and it never changes.  When we view a chart in a computer, where we can zoom in and out on the display, we are changing its scale each time we change the zoom.  So we need new terms.

A specific ENC is almost always based on a specific paper chart (RNC), or predominately on one, which has a unique scale, and that original scale used to make the ENC is called its compilation scale.  We can ask an ENC for its chart properties, and it will report back a scale, which is its compilation scale. The ENC US5WA16M, for example, is based on paper chart 18471 which has a scale of 1:40,000 so the ENC has a compilation scale of 1:40,000.  (This relationship between paper chart scales and ENC scales will eventually change with NOAA's ongoing rescheming program, but that is the way most ENC are for now.)

Viewing this ENC on a computer screen, we can zoom in and out, ending up with various scales. The scale we happen to be looking at is called the display scale.  Nav programs let us view this scale on the screen as we zoom in and out. The display scale can be larger or smaller than the compilation scale. In principle, the scale shown has the same meaning we are used to with paper charts. Namely viewing a chart at a display scale of 1:44,882 should mean that 1 inch on the screen is 44,882 inches on the charted ground. Some programs are fairly good at this, others less so. It is an easy thing to check comparing with the RNC of the same area.

In principle, any one ENC is intended to be viewed at the compilation scale for crucial navigation, with the obvious knowledge that the user is going to zoom in and out to meet their needs. Keeping in mind that the scale names "go backwards" in a sense, the table below reminds us what zooming means.


When we zoom in we are going to larger scales, and land in view will get larger as we do so, but the actual scale values will be getting smaller. 

With this background we can now look at a unique property of all ENC objects. They each have an attribute called Scale minimum abbreviated SCAMIN. SCAMIN is the minimum display scale that will show a specific object on a specific chart.  Below are a few samples of how SCAMIN values can change with chart scale.


Charts in the top two groups have overlapping coverage of at least one of the objects listed; the bottom group are adjacent and overlapping charts.

If you are viewing the chart at a display scale equal to the compilation scale, and you zoom out from there in steps (going to larger scale numbers), then at some point the object you are looking at will disappear. This happens when your display scale equals the SCAMIN value. 

The diagram shows SCAMIN + 1, because the SCAMIN values are encoded in the ENC as 1 less than a common chart scale. Thus we do not see SCAMIN = 1:12,000; we would see SCAMIN = 1:11,999. This is presumably done to prevent rounding errors at the transitions. We have just undone this here for clarity.

Thus SCAMIN has a couple effects on our practical navigation.  Zooming out, it keeps the charts from getting too cluttered by removing objects we might not be looking for on smaller scales, but in doing so, it might well be hiding an object we are looking for. Thus we have to be mindful of SCAMIN values and how they work. It is called "scale minimum," which means the smallest scale it shows on, which we have to recall means the largest "scale number" it will show on.

Plus there are several subtitles we have to be on the lookout for. A lighthouse might on one chart be called a Landmark (LNDMRK) and on another chart be called a Single building (BUISGL). Recall that on ENC, we do not have lighthouses, we have LIGHTS and we have objects (LNDMRK or BUISGL) whose FUNCTN attribute is Light support. On a 1:10,000 chart, the former is in view all the way to 1:22,000, where things are half the size they are compilation scale, but the latter goes away at 1:12,000, where these same things have only diminished in size by 10 or 20%. Depending on your nav program and how you have it set up, starting from the compilation scale, the former is in view for 10 steps of zoom, whereas the latter goes away in one step.

Another issue comes up when two adjacent or overlapping charts have notably different SCAMIN for the same object. Then you can see an object bounce in and out of view as you change charts.

In extreme cases, if you ignore all the many safety features built into an ENC and a good nav program or ECDIS, then you could in principle view a chart at the compilation scale and then zoom out enough to hide a dangerous sounding and then navigating on that scale you hit it. There are articles online about ships doing that, but you have to do so many things wrong to get to that point that this is not a serious concern. The use of ENC safety contours and alarm-triggering COG predictors will prevent this, not to mention going over a planned route carefully once set up, which is standard procedure.
___________________

So with SCAMIN we see that zooming out from the compilation scale by something like a factor of two or so (i.e., going from 1:40,000 to 1:80,000) can remove objects from view. This is sometimes called "under zooming." 

Going the other direction, zooming in from the compilation scale by a factor of two or more (i.e., going from 1:40,000 to 1:20,000) is called "over zooming," and this has its consequences as well, although it is not uncommon to do so with caution in routine navigation. The primary consequence is we risk displaying chart details at a level that is beyond their actual accuracy. Because of that, nav programs have various ways to alert mariners to an over zoomed chart, usually with a prominent announcement on the screen.

Type approved ECDIS cover an over-zoomed chart with a grid of parallel lines, but this is considered more than needed by most unofficial electronic charting systems (ECS). We have notes elsewhere on over zooming as well as how we tell what the base accuracy of the charted objects is to begin with.


Monday, September 20, 2021

Online ENC Object Catalogs

Everything shown on an electronic navigational chart (ENC) is called an object, and each object has a set of attributes that describe its details. The concept is discussed in this article about ENC terminology.

Our textbook Introduction to Electronic Chart Navigation has a list of all ENC objects and all attributes, but it does not include all the possible values of each of the attributes for all of the objects. This would be many pages of fine print.  We have an example online that shows the complexity: Landmarks in ENC. Looking at that we cannot help but say, "We need an app for that, " and indeed there are online resources that do just that. They are called, reasonably enough, ENC Object Catalogs.

An easy one to remember is this resource from Russia:

www.S-57.com

The name comes from the IHO standard for ENC content, called IHO Transfer Standard For Digital Hydrographic Data, Edition 3.1, Special Publication No. 57, usually referred to as simply "S-57."  This is a complex document that refers to what should be in the ENC—it does not, however, specify how the information should be displayed on our screens. The rules for the display are in another complex document called S-52.

The landing page of s-57.com looks like this:


You can click the image for a larger view, or to get even larger view, open image in another tab and then enlarge. This applies to all Blog post images.

The objects are on the left and the attributes on the right. Click one of the blue Attributes on the left to load it into the right side where you see the various values that attribute can have.

There is a Help file provided, but besides giving the references does not add much. We learn that red warnings that say "Deleted objects, do not use" means just that. They list here 501 objects, of which some 400 are active. Not clear why they keep the invalid ones, but I think this site has not been maintained for many years.

Find the object you want, or look over what is there, with the object dropdown arrow. You can type the first letter of your object, but it will not search beyond that one. 

The objects's abbreviation is also listed, but these are not known to those new to ENC. The IHO and IMO discourages the use of these abbreviations, but they can in fact be convenient in some cases. The IHO calls these "acronyms," but this stretches the common English definition of the term. 


Once you  load the attribute of interest on the right, you can see the optional values and also do a mouse over the meaning column to get its official definition. 

Likewise, in the INT1 column, any item that is underlined is a live link to pop up the international paper chart symbol.  The INT 1 symbol is the one that appears in the first column of the Chart No. 1 booklet of chart symbols.


Section of a page from Chart No. 1.  We have an ECDIS version of this in our textbook.

For each object we see three types of attributes listed: A, B, and C



Set Attribute_A: "attributes in this subset define the individual characteristics of an object."

These are the main properties of the object. In this case of a lateral buoy: Buoy shape, Category of the buoy, Color, Color pattern, and so on. Click each one to see on the right panel what it means and what its value is. In this catalog, just ignore any item that has a line through it. Type A attributes do not change on various charts and scales.

Key here is the indicator (!) which means this is a mandatory attribute. (!?) means it is a conditionally mandatory, i.e., if more than one color is given in the Color attribute, then the Color pattern attribute must be given.

The Definition, References, Remarks, and Distinctions shown here are those of the object itself.

Set Attribute_B: "attributes in this subset provide information relevant to the use of the data, e.g. for presentation or for an information system."

This set has the same components for all objects, but their values change from one object to the next, and they can change for the same object viewed on different charts. INFORM and TXTDSC are text presentations of notes we see on the printed charts or details about the chart itself. These often include links to text files that are part of the ENC. These attributes are crucial to chart work, but easy to use and interpret. A leading N in the attribute name means it is this same information in the national language of the chart producer. 

The more subtle and important type-B attribute is SCAMIN,  the minimum display scale that an object will appear on. We have a separate note on Role of SCAMIN on ENC.

Set Attribute_C: "attributes in this subset provide administrative information about the object and the data describing it."
___________

A second online ENC Object Catalog is provided by Teledyne CARIS, a long standing Canadian-American company specializing in GIS and related technologies.


This one is a bit  faster to use providing you know the abbreviations for the objects or attributes of interest. We can be more confident that this one is up to date. It also has all the attribute definitions in a single file that might be more convenient for some  applications. 

It is valuable to know about this one, but the list of plain language names of objects and attributes in the one above makes it a more logical place to start with these resources.





How to Activate a Color Filter on iPhones for Night Vision

We have three nav apps for iOS (StarPilot and Marine Barograph) that would likely be used at night at some point, so here is a way to help protect night vision when using your iPhone or iPad.

In Settings choose Accessibility


Scroll to bottom to Accessibility Shortcut 


Note at the top it gives specific phone-dependent instructions for engaging the shortcuts.


Put a check on Color Filters


Go back to Accessibility and go to  Display & Text Size  (near the top)


From Display and text size, click Color Filters, and turn it on at the top, Check mark Color Tint.


Slide HUE all the way right to get Red, then choose INTENSITY level with slider above that you want—it will have to be pretty far right to be effective.


Done. Can close Settings.


Then you can turn this on and off with a triple click of the side button or home button on your phone, depending on model.


Note if you have other Accessibility shortcuts checked, you choose between them with the triple click.

Wednesday, September 8, 2021

Landmarks on ENC: The Nuts and Bolts

We have several articles on the role of objects and attributes as used in electronic navigational charts (ENC). Background articles are listed at the end here. In each of these, when it came to the nuts and bolts of this topic, we had to punt, so everyone would not fall asleep. Here is where such a punt might land, namely we take a look at one ENC object, Landmarks, and the primary attributes that ENC include or might include. The object definition is:

LandmarkA prominent object at a fixed location which can be used in determining a location or a direction (adapted from IHO Dictionary, S-32, 5th Edition, 2643).

This object has many attributes because it has such a broad definition. We list here just the primary ones. Among those not listed are: its height (HEIGHT), which is above MHW; we could measure that with a sextant (top of the object to the waterline below it) to get distance off. This is not to be confused with its elevation (ELEVAT) which is above MSL, nor with its actual height above the ground, called its vertical length (VERLEN).  The attributes marked * are the only actual required ones, but landmarks typically include Function as well. If more than one color is specified, then the color pattern must also be given, which is indicated by the # 

A radio tower would be a landmark with category = tower (17) and function = radio (31); if visually conspicuous, its symbol would be a black outline, else it would be brown.  The US only plots a few of the non-conspicuous landmarks, but other nations do a lot more in theirs.

Landmark symbols on an ENC

The main takeaway here is the ENC can include a lot more information than the corresponding paper chart does, although not all of the known information is encoded at present. This is where mariners can help by reporting new or outdated information to NOAA. The charts are updated weekly.

Below are the options are for the primary attributes of object Landmark. 

Object Attributes
Landmark *Category, *Conspicuous visually, Function, Color, #Color pattern, Status, Condition, Conspicuous radar
LNDMRK CATLAM, CONVIS, FUNCTN, COLOUR, COLPAT, STATUS, CONDTN, CONRAD
 
CATLAM Category of the landmark
1 cairn: a mound of stones, usually conical or pyramidal, raised as a landmark or to designate a point of importance in surveying. (IHO Dictionary, S-32, 5th Edition, 601)
2 cemetery: an area of land for burying the dead.
3 chimney: a vertical structure containing a passage or flue for discharging smoke and gases. (Digital Geographic Information Standard - DIGEST)
4 dish aerial: a parabolic aerial for the receipt and transmission of high frequency radio signals. (IHO Dictionary, S-32, 5th Edition, 1400)
5 flagstaff (flagpole): a staff or pole on which flags are raised. (Digital Geographic Information Standard -DIGEST 1.28)
6 flare stack: a tall structure used for burning-off waste oil or gas. (IHO Dictionary, S-32, 5th Edition, 1836). Normally showing a flame and located at refineries (IHO Chart specifications, S-4).
7 mast: a straight vertical piece of timber or a hollow cylinder. (adapted from Digital Geographic Information Standard - DIGEST)
8 wind sock: a tapered fabric sleeve mounted so as to catch and swing with the wind, thus indicating the wind direction. (Navigation dictionary, US National Oceanic and Atmospheric Administration - NOAA, 1969)
9 monument: a structure erected or maintained as a memorial to a person or event. (Digital Geographic Information Standard - DIGEST)
10 column (pillar): a cylindrical or slightly tapering body of considerably greater length than diameter erected vertically. (Oxford English Dictionary)
11 memorial plaque: a slab of metal, usually ornamented, erected as a memorial to a person or event.
12 obelisk: a tapering shaft usually of stone or concrete, square or rectangular in section, with a pyramidal apex. (Adapted from Oxford English Dictionary)
13 statue: a representation of a human, animal or fantasy figure in marble, bronze, etc.
14 cross: a monument, or other structure in form of a cross. (Funk & Wagnalls Dictionary)
15 dome: a landmark comprising a hemispherical or spheroidal shaped structure (adapted from the Macquarie Dictionary).
16 radar scanner: a device used for directing a radar beam through a search pattern (adapted from Navigation Dictionary, US National Oceanic and Atmospheric Administration -NOAA, 1969)
17 tower: a relatively tall structure which may be used for observation, support, storage or communication etc. (Digital Geographic Information Working Group -DGIWG, Oct. 1987)
18 windmill: a wind driven system of vanes attached to a tower like structure (excluding wind-generated power plants). (Digital Geographic Information Standard - DIGEST)
19 windmotor: a modern structure for the use of windpower. (IHO Chart Specifications, S-4)
20 spire/minaret: a tall conical or pyramid-shaped structure often built on the roof or tower of a building, especially a church or mosque. (adapted from The New Shorter Oxford English Dictionary, 1993)
21 large rock or boulder on land: an isolated rocky formation or a single large stone (IHO Dictionary, S-32, 5th Edition 4415)
22 rock pinnacle: high tower or spire-shaped pillar of rock, alone or cresting a summit (adapted from IHO Dictionary, S-32, 5th Edition 3852)
 
CONVIS Conspicuous, visually
1 visually conspicuous: term applied to an object either natural or artificial which is distinctly and notably visible from seaward. (IHO Dictionary, S-32, 5th Edition, 984)
2 not visually conspicuous: an object which is visible from seaward, but is not conspicuous.
 
FUNCTN Function of the landmark
1 No function / service of major interest:
2 harbour-master's office: the office of the local official who has charge of mooring and berthing of vessels, collecting harbour fees, etc. (adapted from IHO Dictionary, S-32, 5th Edition, 2191)
3 customs office: an office which is charged with enforcing customs regulations.
4 health office: the office which is charged with the administration of health laws and sanitary inspections. (adapted from The New Shorter Oxford English Dictionary, 1993)
5 hospital: an institution or establishment providing medical or surgical treatment for the ill or wounded. (The New Shorter Oxford English Dictionary, 1993)
6 post office: the public department, agency or organisation responsible primarily for the collection, transmission and distribution of mail. (The New Shorter Oxford English Dictionary, 1993)
7 hotel: an establishment, especially of a comfortable or luxurious kind, where paying visitors are provided with accommodation, meals and other services. (The New Shorter Oxford English Dictionary, 1993)
8 railway station: a building with platforms where trains arrive, load, discharge and depart. (The New Shorter Oxford English Dictionary, 1993)
9 police station: the office of the local police force.
10 water-police station: the headquarters of a local water-police force.
11 pilot office: the office or headquarters of pilots; the place where the services of a pilot may be obtained. (IHO Dictionary, S-32, 5th Edition, 3845)
12 pilot lookout: a distinctive structure on shore from which personnel keep watch upon events at sea or along the coast. (IHO Dictionary, S-32, 5th Edition, 2917)
13 bank office: an office for custody, deposit, loan, exchange or issue of money. (adapted from The New Shorter Oxford English Dictionary, 1993)
14 headquarters for district control: the quarters of an executive officer (director, manager, etc.) with responsibility for an administrative area.
15 transit shed/warehouse: a building or part of a building for storage of wares or goods. (adapted from The New Shorter Oxford English Dictionary, 1993)
16 factory: a building or buildings with equipment for manufacturing; a workshop. (The New Shorter Oxford English Dictionary, 1993)
17 power station: a stationary plant containing apparatus for large scale conversion of some form of energy (such as hydraulic, steam, chemical or nuclear energy) into electrical energy. (McGraw-Hill Dictionary of Scientific and Technical Terms, 3rd Edition, 1984)
18 administrative: a building for the management of affairs. (adapted from The New Shorter Oxford English Dictionary, 1993)
19 educational facility: a building concerned with education (eg. school, college, university, etc.)
20 church: a building for public Christian worship. (The New Shorter Oxford English Dictionary, 1993)
21 chapel: a place for Christian worship other than a parish, cathedral or church, especially one attached to a private house or institution. (The New Shorter Oxford English Dictionary, 1993)
22 temple: a building for public Jewish worship. (adapted from The New Shorter Oxford English Dictionary, 1993)
23 pagoda: a Hindu or Buddhist temple or sacred building. (The New Shorter Oxford English Dictionary, 1993)
24 shinto shrine: a building for public Shinto worship. (adapted from The New Shorter Oxford English Dictionary, 1993)
25 buddhist temple: see pagoda.
26 mosque: a Muslim place of worship. (The New Shorter Oxford English Dictionary, 1993)
27 marabout: a shrine marking the burial place of a Muslim holy man. (The New Shorter Oxford English Dictionary, 1993)
28 lookout: keeping a watch upon events at sea or along the coast. (adapted from IHO Dictionary, S-32,5th Edition,2917)
29 communication: transmitting and/or receiving electronic communication signals. (adapted from Digital Geographic Information Standard - DIGEST)
30 television: broadcast of television signals.
31 radio: broadcast of radio signals.
32 radar: a method, system or technique of using beamed, reflected, and timed radio waves for detecting, locating, or tracking objects, and for measuring altitudes. (IHO Dictionary, S-32, 5th Edition,4158)
33 light support: supporting a light
34 microwave: broadcasting and receiving signals using microwaves.
35 cooling: dissipating heat.
36 observation: a place from which the surroundings can be observed but at which a watch is not habitually maintained. (adapted from IHO Dictionary, S-32, 5th Edition,2917)
37 time ball: a visual time signal in form of a ball
38 clock: visual time signal. (adapted from S-32, 5th Edition, 5536)
39 control: used to control the flow of air, rail, or marine traffic. (Digital Geographic Information Standard - DIGEST)
40 airship mooring: a facility to secure an airship. (adapted from Digital Geographic Information Standard - DIGEST)
41 stadium: a large usually unroofed building with tiers of seats for spectators
42 bus station: a location at which buses arrive and from which they depart.
 
COLOUR Color of landmark
1 white
2 black
3 red
4 green
5 blue
6 yellow
7 grey
8 brown
9 amber
10 violet
11 orange
12 magenta
13 pink
 
COLPAT Color pattern
1 horizontal stripes: straight bands or stripes of differing colours painted horizontally.
2 vertical stripes: straight bands or stripes of differing colours painted vertically.
3 diagonal stripes: straight bands or stripes of differing colours painted diagonally (ie not horizontally or vertically).
4 squared: often referred to as checker plate, where alternate colours are used to create squares similar to a chess or draught board. The pattern may be straight or diagonal.
5 stripes (direction unknown): straight bands or stripes of differing colours painted in an unknown direction.
6 border stripe: a band or stripe of colour which is displayed around the outer edge of the object, which may also form a border to an inner pattern or plain colour.
 
CONDTN Condition of the landmark
1 under construction: a structure that is in the process of being built.
2 ruined: a structure in a decayed or deteriorated condition resulting from neglect or disuse, or a damaged structure in need of repair. (IHO Dictionary, S-32, 5th Edition, 4456)
3 under reclamation: an area of the sea that is being reclaimed as land, usually by the dumping of earth and other material.
4 wingless: a windmill or windmotor from which the turbine blades are missing.
5 planned construction: an area where a future construction is planned.
 
STATUS Status of landmark
1 permanent: intended to last or function indefinitely. (The Concise Oxford Dictionary, 7th Edition)
2 occasional: acting on special occasions; happening irregularly. (The Concise Oxford Dictionary, 7th Edition)
3 recommended: presented as worthy of confidence, acceptance, use, etc. (The Macquarie Dictionary, 1988)
4 not in use: no longer used for the purpose intended; disused.
5 periodic/intermittent: recurring at intervals. (The Concise Oxford Dictionary, 7th Edition)
6 reserved: set apart for some specific use. (adapted from The Concise Oxford Dictionary, 7th Edition)
7 temporary: meant to last only for a time. (The Concise Oxford Dictionary)
8 private: not in public ownership or operation.
9 mandatory: compulsory; enforced. (The Concise Oxford Dictionary, 7th Edition)
10
11 extinguished: no longer lit illuminated: lit by floodlights, strip lights, etc.
12 illuminated: lit by floodlights, strip lights, etc.
13 historic: famous in history; of historical interest. (The Concise Oxford Dictionary, 7th Edition)
14 public: belonging to, available to, used or shared by, the community as a whole and not restricted to private use. (adapted from The New Shorter Oxford English Dictionary, 1993)
15 synchronized: occur at a time, coincide in point of time, be contemporary or simultaneous. (The New Shorter Oxford English Dictionary, 1993)
16 watched: looked at or observed over a period of time especially so as to be aware of any movement or change. (adapted from The New Shorter Oxford English Dictionary, 1993)
17 un-watched: usually automatic in operation, without any permanently-stationed personnel to superintend it. (adapted from IHO Dictionary, S-32, 5th Edition, 2814)
18 existence doubtful: an object that has been reported but has not been definitely determined to exist.
 
CONRAD Conspicuous by radar
1 radar conspicuous: an object which returns a strong radar echo. (IHO Dictionary, S-32, 5th Edition, 4142)
2 not radar conspicuous: an object which does not return a particularly strong radar echo.
3 radar conspicuous (has radar reflector): an object which returns a strong radar echo, having a radar reflector.

Background articles include:

Monday, September 6, 2021

Where Have All the Towers Gone? — Getting Into ENC Terminology

As you may know, NOAA is well into the process of sunsetting all paper charts, which is their way of saying they are replacing them with electronic navigational charts (ENC) and the new NOAA Custom Charts (NCC), a user designed and printed hybrid of the new and the old. This process will be complete (meaning no traditional paper charts left at all) by the end of 2024.

The ENC are indeed better than the traditional charts we are used to, but they are now all electronic products—even the new ones (NCC) that we print ourselves are based on the digital ENC. As such, they are effectively databases of charted objects, along with multiple attributes for each object. Both objects and attributes have 6-letter abbreviations.  


One type of object, for example, would be a Lateral buoy (BOYLAT). This object can have multiple attributes. It must have an attribute Buoy shape (BOYSHP), which In turn will have one of eight different values, including the common ones, 1=conical, 2=can, 3=spherical, etc. It must also have attribute Category of lateral mark (CATLAM), which can be 1=port side, 2=starboard side, 3=preferred to starboard, or 4= preferred to port.


It must also have attribute Color (COLOUR), which can have thirteen values, and it must have an attribute Color pattern (COLPAT) which has 6 possible values, starting with 1=horizontal stripes, 2=vertical stripes, etc.


Besides these required attributes, the object BOYLAT could have an attribute Object name (OBJNAM), which is common, and it could have its height specified as its Vertical length (VERLEN), but this is rare. And it has an attribute Conspicuous by radar (CONRAD) with values 1=radar conspicuous, 2=not radar conspicuous, 3=has radar reflector…  and other attributes, such as its Status (STATUS), which has eighteen values including 1=permanent, 7=temporary, 8=private, and so on. Plus half a dozen more attributes, including Scale minimum (SCAMIN), which is the minimum displayed chart scale required for this object to show up on the display—a unique property of ENC, but this one can be overridden by user controls.


We see that this new chart object structure is all very specific, but we note that a light or bell or racon is somehow no longer an attribute of the buoy. Before we had lighted buoys; now we have lights and we have buoys, and we have fog signals, and we have racons. These are now all separate objects, and each of these objects will have its own set of attributes. The list of attributes for a Light (object LIGHTS) is long and complex.


When an experienced navigator looks over the list of some 400 charted objects, two things stand out immediately: there is no object called "Tower," and even more surprising, there is no charted object called "Rock." This is one of the moments when we question whether we are going to like this new chart system or not! On the other hand, this is not at all a problem for someone brand new to navigation, who has not worked with paper charts for years. They do not have the muscle memory of the role these objects played in their lives for so long.


But after a few deep breaths, we realize that if we are to organize charted objects into logical categories, we can think of a tower as a type of landmark, which is indeed how this works. We have the chart object Landmark (LNDMRK), which has an attribute Category of landmark (CATLMK) that takes on one of twenty options, such as 3=chimney, 9=monument, or 17=tower. We can also have cairn, mast, statue, windmill, and so on. 



Paper chart (RNC) on the left. ENC on the right do not have labels for landmarks unless it has an Object Name (OBJNAM), but they do have different symbols for different values of CATLMK and FUNCTN. These are views from OpenCPNs split screen option. The inserts are the pick reports from the ENC chart on the right. In passing, note that RNC sector lights mark where the light is obscured, but ENC marks the area where they can be seen.



This is certainly a manageable structure to Iive with, but we have to deep breathe again when we learn that landmark objects will most likely not have a label on the chart as we are used to in RNC, so we have to click it to read it. This is another part of what we have to learn about the use of electronic navigational charts. The various landmark symbols are shown below from the NOAA Chart No, 1.



The statement top left that non conspicuous landmarks are not shown on NOAA ENC does not seem to be true, but i will have to look more into this. Some do exist, we have practice quizzes using them, but maybe the ones we found are chart errors? There are certainly a lot in Europe on official ENC there.


From this we begin to see benefits over paper charts as well. We learn, for example, that landmarks have another attribute called Visually conspicuous (CONVIS), with values 1=yes and 2=no. Then it turns out that the symbols are subtly different for conspicuous landmarks—they have black outlines, whereas not conspicuous have brown outlines—look out for that one on our quizzes! We do not know if a landmark is conspicuous or not by looking at a tower symbol on a paper chart, just as we likely do not know its color, color pattern, height above the ground, radar observability, and more, which we can learn from an ENC if these data happen to be encoded for that specific landmark. In short, things are different, but once we adapt to that, we see things are better... or certainly potentially better.


Rocks are another story, which I leave to another note. The object is Underwater/awash rock (UWTROC). Unlike paper charts with three rock symbols, all rocks on ENC have the same symbol, which we distinguish with a right click on the asterisk symbol to read the attributes. Also there is a new definition of "awash," which merits its own discussion.


The structure and use of ENC is the main topic of our book on electronic chart navigation.