Advisory notice on "Web Mercator"

4037 NGA raster nautical charts displayed upon Google Maps imagery
(Marine GeoGarage) 

NGA released a cease and desist regarding webmapping products for navigation and targeting due to inaccuracies with the default map.

I just learn that National Geospatial-Intelligence Agency (NGA) published some recent documents (February & May 2014) regarding the use of Web Mercator projection originally adopted by the leaders of the Internet (created for Google Maps, then adopted for Microsoft Virtual Earth, Yahoo Maps), and also embraced by other commercial API providers (OpenLayers, Leaflet, ArcGIS for JS...).
This term is used to refer to the fact that these providers use a specific Mercator projection which is neither strictly ellipsoidal, nor strictly spherical.
So this affects calculations done based on processing the map as a flat plane.

 "Maps from G. Mercator are worthless" (translation from French)

I don't say that NGA seems to discover webmapping, 9 years after the introduction of Google Maps in 2005 and the adoption of this specific projection for their maps and imagery, but this is an old debate since the arrival of the first geo web actors, what Dodge & Perkins examined in 2008 as an apparent decline in mapping quality ("McMaps", amateur(ish) maps made by non-experts or neogeographers).
On a technical point of view, Noel Zinn (in 2010) and more recently Daniel Streb (in 2012) have perfectly explained before NGA the technical issues relative to the choice of a pseudo Mercator projection.

In 2009, International Association of Oil & Gas Producers (OGP which created the EPSG codes) described quite well the Coordinate Conversions and Transformations including Formulas for this projection (see the evolution in the time of the EPSG codes for Google Mercator,  not a recognised geodetic system in the last Web Mercator -Auxiliary Sphere- EPSG:3857 version.
"We have reviewed the coordinate reference system used by Microsoft, Google, etc. and believe that it is technically flawed. We will not devalue the EPSG dataset by including such inappropriate geodesy and cartography." said EPSG.

1.3.3.2 Popular Visualization Pseudo Mercator
(EPSG dataset coordinate operation method code 1024)
This method is utilized by some popular web mapping and visualization applications.
It applies standard Mercator (Spherical) formulas (section 1.3.3.1 above) to ellipsoidal coordinates and the sphere radius is taken to be the semi-major axis of the ellipsoid.
This approach only approximates to the more rigorous application of ellipsoidal formulas to ellipsoidal coordinates (as given in EPSG dataset coordinate operation method codes 9804 and 9805 in section 1.3.3 above).
Unlike either the spherical or ellipsoidal Mercator projection methods, this method is not conformal: scale factor varies as a function of azimuth, which creates angular distortion.
Despite angular distortion there is no convergence in the meridian. 

 EPSG definition said in 2006 the projection "uses spherical development of ellipsoidal coordinates."

 extract from OGP publication

So Web Mercator is really a non conformal projection : scale factor in the N/S meridian direction not equal to scale factor in E/W parallel direction : not a constant, but a function of azimuth (direction).
By the way, Google Maps chose for its pseudo Web Mercator to use a radius of the Earth equal to the semimajor axis of the WGS84/GRS80 reference ellipsoid (Equatorial radius : 6,378,137.0 meters), which is much larger than the Mean radius whose value is about 6,371,007.0 meters used in Mercator Spherical).
But actually Web Mercator is "almost conformal" when looking at small areas...
An infinitesimal circle drawed on the ellipsoid surface, would become an ellipse on the map, but an ellipse with a very small flattening, and really similar to a circle.
For this reason deformation of shape is very small too when looking at small areas, and is not visually notable : a square building is projected as a (almost) square building.
For memory, conserving the shape of square buildings was one of the major reason for the choice of this specific pseudo Mercator by the original Google Maps team (Where2 Technologies startup co-founded by Jens and Lars Rasmussen brothers), and adopted by many web maps today.
Note : the first launch of Google Maps actually did not use pseudo Mercator but Plate Carree, and streets in high latitude places like Stockholm did not meet at right angles on the map the way they do in reality.
The majority of Google Maps users are looking down at the street level for businesses, directions, etc...
While this distorts a 'zoomed-out view' of the map, it allows close-ups (street level) to appear more like reality.

with GDAL/PROJ4 tools : delta = 36.3 km at Lat = 58°
echo -5.0 58.0 | cs2cs -f “%.10f” +init=epsg:4326 +to +init=epsg:3395 (Geo2Mercator)
=> -556,597.454, 7,931,049.576
echo -5.0 58.0 | cs2cs -f “%.10f” +init=epsg:4326 +to +init=epsg:3857 (Geo2WebMercator)
=> -556,597.454, 7,967,317.535
The units of web Mercator are not really Meters, they are "Web Mercator Meters"

and they are equal only on the Equator line.

When you go north or south from the Equator line, the ratio (difference in Northing between Mercator and Web Mercator) between the two units is getting bigger.

However, although Web Mercator shares some of the same properties of the standard Mercator projection (north is up everywhere, areas near the poles are greatly exaggerated), rhumb lines (or loxodromes, lines of constant true heading that navigators used to sail before GPS) are not straight lines.

courtesy of Noel Zinn document

So as non-conformal with not straight loxodromes, this projection should not be really called “Mercator” according the terms of IHO : Web Mercator can't be used for navigation.

Actually the aim of Google Maps was at first visualization of maps and aerial/satellite imagery on the web and not to be a tool for accurate surveying computations : Web Mercator wouldn’t be used for surveying, geodetic or scientific purposes.

To simplify the calculations, we use the spherical form of this projection, not the ellipsoidal form. Since the projection is used only for map display, and not for displaying numeric coordinates, we don’t need the extra precision of an ellipsoidal projection. The spherical projection causes approximately 0.33% scale distortion in the Y direction, which is not visually noticeable. 
(source : Bing Maps Tile System)

However, Web Mercator is a projection that maps from ellipsoidal WGS84 LatLon (LL) to XY in Web Mercator meters and back to ellipsoidal LL : so a completely reversible LLXY.
The first version of the public Marine GeoGarage website (unprojecting back plotted waypoints in Web Mercator meters to WGS84 LatLon coordinates) proposed some Route planning tool allowing the user to save the waypoints and routes created with the webmapping in gpx or Garmin formats to be use in GPS or chart plotters.

The loss of conformality implied when using directly the simpler and faster spherical formulas, didn't worry his creators because Google Maps was targeted for the majority of people, so non specialist.
The reason for the creation of this specific pseudo Mercator simplifying mathematical calculations was Javascript performance (scale factor not computed).
Reprojection of the coordinates to the Web Mercator projection (from EPSG:4326 to EPSG:3857):
x = a*λ (a = WGS4 semi-major axis -Equatoril radius- 6,378,137m)
y = a*arctanh(sinφ) − a*e*arctanh(e*sinφ) : eccentricity (e) of the Earth not taken into account (eq 0) in Web Mercator (for info e=0.081819190842621)
so (Lat φ and Lon λ are in radians) about 5 times faster than the ellipsoidal Mercator

 zoom level 1 has 4 square tiles

By the way, in order to get an entire world map similar to a (very large) square (pyramidal tiles : 256 px x 256 px), Google Maps uses some bound in Latitude (85.0511° = arctan(sinh(π))


Web applications are a very important platform because of their ability to reach a large number of people easily.
Web Mercator as the pioneer projection chosen for 2D webmapping became the standard for sharing data on the web because of the richness of the offer in matter of maps and imagery provided by the giants of the Internet.
That's also the main reason why we decided to match the nautical charts with satellite and aerial imagery, in order to align properly with the services such as these popular contents.
-> see GeoGarage blog :
http://blog.geogarage.com/2012/11/south-pacific-sandy-island-proven-not.html
http://blog.geogarage.com/2011/01/bahamas-wlp-update-in-marine-geogarage.html

By the way, we must recall that the GeoGarage nautical charts web and mobile viewers are not to be used as a primary tool for navigation.
The goal is not to replace the existing Electronic Chart System for navigation, but to provide a maritime route planning tool accessible for a large audience.


As the basic quandary is the accuracy issue in 2D Planisphere web viewers, why not approaching reality using a 3D Globe ?

NOAA nautical raster charts in Google Earth from Marine GeoGarage on Vimeo.

Google Earth viewer using re-projecting on the fly individual tiles 
in Mercator to Plate Carree before rendering them.
However kml format proved to not be very adapted for adding a custom streamable large tileset.

In the next future, with the ongoing advent of HTML5 and WebGL, developing virtual globe applications running in the web browser without any plug-in will allow to stay focus on the visualization.

 see video : UKHO Multitouch demo

While the sphere is a close approximation of the true figure of the Earth and satisfactory for many purposes, geodesists have developed a number of models to represent a closer approximation to the shape of the Earth, using a cartesian XYZ coordinate frame of reference (Earth-Centered, Earth-Fixed -ECEF- used in GPS) and datum transformation to the more commonly used geodetic-mapping coordinates of Latitude, Longitude, and Altitude (LLA).
But portraying the reality of our planet as a nearly spherical surface in a three-dimensional world is also a challenge, especially if we plan to integrate altitudes and bathymetry.

 Google Maps (Earth) new version on WebGL-enabled browser

The best of the ellipsoïdal and Geoid models can represent the shape of the earth over the smoothed, averaged sea-surface to within about one-hundred meters.
Through a long history, the "figure of the Earth" was refined from flat-Earth models to spherical models of sufficient accuracy to allow global exploration, navigation and mapping.

Vertical deflection

But like with the use of 2D world viewers on the web, if you work in some field that required accurate maps, you would not necessarily find globes in common use.

 Gerard Mercator's 1541 terrestrial globe on display in the Harvard Map Collection exhibit hall.

Along with a 1551 celestial globe, this is one of only 22 surviving matched pairs in the world, and the only matched pair in America.

The most accurate globe would be a globe the size of earth itself.
Jorge Luis Borges's "On Exactitude in Science" describes the tragic uselessness of the perfectly accurate, one-to-one map (Map as a Territory):
In time, those Unconscionable Maps no longer satisfied, and the Cartographers Guild drew a Map of the Empire whose size was that of the Empire, coinciding point for point with it. The following Generations, who were not so fond of the Study of Cartography saw the vast Map to be Useless and permitted it to decay and fray under the Sun and winters.
In the Deserts of the West, still today, there are Tattered Ruins of the Map, inhabited by Animals and Beggars; and in all the Land there is no other Relic of the Disciplines of Geography.

Links :

• Flattening the Earth: Two Thousand Years of Map Projections by John P. Snyder
• Business Insider : The Most Popular Map Of The World Is Highly Misleading
• The Guardian : Why Google Maps gets Africa wrong 
• GeoGarage blog : Gerardus Mercator : father of modern mapmaking
• ESRI : Measuring distances and areas when your map uses the Web Mercator projection 
• OpenLayers : Spherical Mercator
• How WGS 84 defines Earth
• Scientific American : The Geoid: Why a map of Earth’s gravity yields a potato-shaped planet
• Some Principles of Web Mercator Maps and their Computation 
  
• Rhumb Lines and Map Wars: A Social History of the Mercator Projection (by Mark Monmonier) 

Sea Chair

Sea Chair from Studio Swine
Ingenuity at sea knows no limits.
What should fishermen do with the piles of plastic that come up in their nets?
These UK mariners invented a furnace to melt down plastic scraps and build stools, all while still at sea.
They even put the designs online so that anyone can try their hand at making reclaimed plastic furniture.

Since the discovery of the Pacific Garbage Patch in 1997, which is predicted to measure twice the size of Texas, five more have been found across the world’s oceans with the Atlantic gyre predicted to be even larger.
This plastic takes thousands of years to degrade, remaining in the environment to be broken up into ever smaller fragments by ocean currents.

The gyre stretches from the coastlines of California to the shores of Japan.
Recent studies have estimated 46,000 pieces of plastic per square kilometer of the world’s oceans.
The number of plastic pieces in the Pacific Ocean has tripled in the last ten years and the size of the accumulation is set to double in the next ten.

Sea Chair is made entirely from plastic recovered from our oceans.
Together with local fishermen, Studio Swine collects and processes the marine plastic into a stool at sea.

We thought we had seen everything in freediving

We thought we had seen everything in freediving from FreedivingUAE

Do you have any hidden talents or any special tricks you can do?

Maybe it’s moving your tongue in a special way or being extremely flexible.

David Helderle can do something absolutely amazing.

The funny thing is, he didn’t think it was anything special until a freediving veteran saw him doing it and was dumbfounded not only by the feat itself, but by the way David seemed to do it so effortlessly.

So what’s Helder's special ability?

He can create mini vortexes that shoot through the water to create intricate patterns in just about any direction.

That may not sound like much, but anyone who has tried freediving or even just been messing around in the water knows that it’s no easy task to control water the way he can.

Seeing is believing so watch the video above to see this one of a kind “magic” show on display for yourself.

We sat down with the 40 year old Frenchman to find out a bit more about his story and found a passionate freediver who believes that it’s more than just a sport but rather, “something spiritual” that provides him with an escape from the stress of daily life where he feels that we are normally forced to show an altered version of ourselves.

For him, being below the surface gives him a chance to be true to himself without having to put on any acts or trying to convince anyone that he is anything other than David.

“You can knock at my door,” says Helder , “and I will not answer because I’m not there.”

More than anything, it’s the meditative qualities of freediving and the chance to be “someone else” that have this 35 year freediving veteran so excited about the next dive.

It was his father, a freediver in his own right, that got young David started around age 4.
It hasn’t all been easy though.

His worst failure came around age 12 when,

“I had a blackout when doing dynamic inside a pool. I [was] rescued by a friend who was acting as a buddy. At that time, I was trying to find a different path than the one taught by my dad and my breath up was a mix of hyperventilating followed by a slow belly breathing. That technique led me to the blackout. I then decided that performing a slow belly breathing prior to a dive was definitely the only right way to freedive safely!”

When asked about his biggest success, Helder responds with a smile and says,

“Staying enough time underwater to make some friends: Clown fish and groupers are very friendly!!”

David’s advice to anyone thinking about freediving or trying to improve their skills is to dive without a watch. In his opinion, that frees up your mind to relax and focus on the sensations around you. While he doesn’t have any inspirational quotes to share, Helder leaves us with his own parting words of wisdom that make his passion about freediving abundantly clear:

“…if I am freediving it ‘s to find peace beyond thoughts and words. Freediving is taking a retreat.”

Be sure to watch the video to see some stunning footage of David’s underwater vortexes and some of the marine life he encounters on his adventures.

Pay special attention to the tricks he does around minute 2:40 if you want to see a really impressive display of his talents.

Casualties of the Nautical Chart

From Hydro by Ian Russell (article in PDF)

What You See is Not Always What You Get

When ships run aground unexpectedly the initial presumption is that the vessel has struck an ‘uncharted’ feature.
In practice this is rarely so.
This article reviews a number of chart-related casualties.
These demonstrate that while no charts are infallible, a better appreciation of their limitations might have averted disaster.
New cruise ship itineraries in tropical seas and Polar Regions require especial vigilance.
Ever deeper draught bulk cargo and crude carriers are transiting sparsely surveyed ocean areas and accessing remote locations in the continuing search for and exploitation of new mineral deposits.
Are these accidents waiting to happen?


Today’s navigators often 
venture where available hydrographic data does not meet the requirements of contemporary shipping.
Member States of the International Hydrographic Organization (IHO) acknowledge this deficiency and are pledged to remedy it; but this will take time.
The circumstances leading to past mishaps are therefore ­potentially present both now and in future. Although the charts in use in some of the cited casualties were compiled from lead-line surveys; they provided ample evidence that less water than charted might be expected.
Accounts of accidents often reveal the vessel’s speed to have been excessive in the circumstances.
The IHO defines inadequately surveyed areas as those where bathymetry is based on older lead-line surveys or other surveys which are either open in nature or not hydrographic surveys.
International Maritime Organisation (IMO) Guidelines on Voyage Planning for Passenger Ships Operating in Remote Areas, adopted in 2007, indicate that planning should take into account the source, date and quality of the hydrographic data of charts used.
Navigators should remember that the nearest point of land is almost always the seabed, as the case studies demonstrate.

Case 1 (Caribbean Calamity) 

In January 1971, the former French passenger liner Antilles (length over all (l.o.a.) 183m, beam 24.4m, draught 8m) struck an uncharted reef off the NW coast of Mustique in the Grenadine Islands. As the ship was proceeding at 16 knots the impact caused her to break in two and catch fire.

 Mustique island with the Marine GeoGarage (NGA chart)

The passage being attempted was through apparently open water some 640m wide, with charted depths of 13 and 16 metres.
It lay between two rock outcrops, in a coral and reef-strewn area last surveyed in the 19th century.
This followed a change to the planned route; authorized by the master in order, as the subsequent legal proceedings revealed, ‘to provide his passengers with a better look at this enchanting isle and was consistent with his desire to implement the Owner’s policy of making Antilles’ cruises entertaining and unique’.

Case 2 (Déja vu) 

In April 2000, the ‘Adventure’ cruise ship World Discoverer (l.o.a. 87m, beam 15m, draught 4.57m) grounded on an allegedly uncharted feature in Sandfly Passage, Solomon Islands.

Figure 1: World Discoverer.

Image courtesy: Philjones828, via Wikimedia Commons.


The ship was fatally holed and the master beached her in Roderick Dhu Bay, where the hulk remains.

Sandfly passage and Roderick Dhu Bay (NGA chart #82377)
with the Marine GeoGarage

Neither the Australian Hydrographic Service nor the UK Hydrographic Office, the Primary Charting Authority, has any record of the incident.

The stranded wreck of World Discoverer is clearly visible on Google Earth,

 Geolocalization with Google Maps imagery

but is not shown on the latest (2012) edition of chart BA 1713. (GeoGarage note : scale too low)

 Figure 1a: Portion of Chart BA1713.

Image courtesy: Crown Copyright and/or database rights.

Reproduced by permission of the Controller of Her Majesty’s Stationery Office and the UK Hydrographic Office

The Pacific Island Pilot, current at the date of the incident, advises that “Deep-draught vessels should not attempt the passage owing to the reefs in the N entrance.”
The latest (2007) edition of the Pilot directs vessels west of Mid Reef; passing clear of the 9.1m patch.
This remains the least depth shown in the passage other than the reef itself.

Case 3 (Uncharted but not ­Unexpected) 


Such dangers also exist for large cargo vessels navigating in poorly charted waters.
In 2010, the bulk carrier Noble Hawk (l.o.a.190m, beam 33m, draught 12.5m), outbound from Teluk Buli in Eastern Indonesia to China, grounded on an uncharted 5m shoal.
Surrounding depths were 53 to 58m.
Her course lay across a large bay encumbered with islets, reefs and shoals.

 Teluk Buli Bay with the Marine GeoGarage (NGA chart)

 

Figure 2: Sketch map derived from Chart BA 2788 (Halmahera and the Adjacent Islands),

compiled from 20th century lead-line surveys, showing position of grounding in relation to Noble Hawk’s departure point, adjacent depths and shoal areas. 


The chart in use was compiled from 20th century lead-line surveys.
In 2012, the Indonesian Navy Hydrographic Service (DISHIDROS) carried out a survey of the grounding site and found a least depth of 3m and an adjacent depth of 15.3m in general depths of 50m.
Mindful of the significant activity of large cruise ships and bulk carriers in these waters DISHIDROS recommended that the new shoal be marked.

Case 4 (Ennerdale Rocks) 


In 1970, a Royal Fleet Auxiliary vessel the tanker Ennerdale (l.o.a. 227m, beam 30m, draught 12m) struck a rock pinnacle about 8 miles NNE of Port Victoria in the Seychelles and sank.

 1 June 1970 whilst outbound from Port Victoria, Mahe in the Seychelles Islands to refuel the frigate HMS ANDROMEDA she struck an uncharted pinnacle of rock in position 04.30 N 055.31 E which opened up her starboard side and she heeled over very quickly and settled on the bottom with her stern section submerged and her bow in the air fortunately without any loss of life

source : historicalrfa.org

The pinnacle, which was charted at 9 fms (16.5m), lay adjacent to a 10 fm (18.3m) sounding in general depths of 13 to16 fms (23.8 to 29.3m).
The vessel, travelling at 12kts, was crossing a line of pinnacles and islet outcrops which extend north-eastwards from the north tip of the Island of Mahé within the 20 fathom line.
The chart in use was compiled from a 19th century lead-line survey, as stated in the title.
The least depth of water over the pinnacle (subsequently established at 10.8m (35ft)) was not shown on this chart.
However, there was sufficient indication on the chart that shoaler water may well have existed in the vicinity.

 Ennerdale rocks with the Marine GeoGarage (British Admiralty chart)

Figure 3: Portion of Chart BA 1072, current at the time of the grounding, showing the 9 fathom shoal patch on which the vessel struck and the adjacent 10 fathom patch.
Image courtesy: Crown Copyright and/or database rights.
Reproduced by permission of the Controller of Her Majesty’s Stationery Office
and the UK Hydrographic Office

The previously unnamed feature is now charted as Ennerdale Rocks.

Cases 5 & 6 (Dangers of the Deep) 


In 1973, the cargo ship Muirfield, drawing 16m, was on passage from the Cape of Good Hope to Selat Sunda.
There was a 2-3m swell running when she struck the top of a seamount, 75 miles south west of the Cocos Islands.

 Murfield seamount with the Marine GeoGarage (AHS chart)

A subsequent survey found a shoal with a least depth of 18m in charted depths of over 5,000m.

Submarine Surprised 


More than 90% of all seamounts greater than 1km in height (estimated to be more than 100,000) are unobserved by either ship soundings or satellite gravity (Sandwell & Wessel, 2010).
This observation is consistent with the statement in IHO publication C-55 that renewed attention needs to be given to the disproving of vigias especially adjacent to the maritime shipping routes in the Pacific and adjacent seas.
The danger to submarine navigation is self evident.
In 2005 USS San Francisco, a nuclear powered submarine, collided with a seamount about 364 nautical miles southeast of Guam. (see NYTimes)

 San Francisco dry-docked at Guam on January 27,2005

source : navsource.org

The submarine was travelling at maximum speed at a depth of 160m.
The seamount that she struck did not appear on the chart in use at the time of the accident.
Other charts available showed an area of ‘discoloured water’, an indication of the probable presence of a seamount.

 South of Guam with the Marine GeoGarage (NGA chart)

Subsequent investigation determined that information regarding the seamount should have been transferred to the charts in use, particularly given the relatively uncharted nature of the ocean area that was being transited. (source : navy.mil)

Discussion 


Figure 3 The progressive increase in the size of vessels.
The dimensions of those now at sea and on order,
reflect the shipping industry’s response to changing operational and trading patterns.


Despite a steady increase in the length of cruise ships the draught of the current vessels in service has not increased proportionately and averages 8.4m.
However, these ships are venturing into increasingly remote and poorly charted areas. Itineraries that seek to provide optimum passenger experience are potentially hazardous.
Many of the smaller vessels (l.o.a. <100m) that offer adventure cruises are fitted with forward looking sonar and can deploy portable echo sounders in their tenders.
The report of an investigation into the incident in the Canadian Artic highlights the necessity for such provision.
The significant draughts in Figure 3 are those of the large cargo vessels.
New Panamax vessels transiting the Caribbean may not be able to do so with the same confidence as their predecessors.
Elsewhere ULCC and large bulk carriers are vulnerable to an encounter with an uncharted seamount rising close to the surface.
In the deep areas of the ocean, most mariners consider that there is little chance of a vessel running aground on such a feature.
Unfortunately, this is a misconception.

 Vema seamount with the Marine GeoGarage (NGA chart)

Examples of navigationally significant seamounts include Vema Seamount (with a charted depth of 11 metres - about 1,000km west-north-west of Cape Town)

Walter shoals with the Marine GeoGarage (NGA chart)

and Walters Shoal Seamount (with a charted depth of 15 metres - about 400 nautical miles south of Madagascar).
 
These seamounts rise up from ocean depths of about 4,000 and 2,000 metres respectively.
(see AWI last seamounts discoveries, June 2014)


Conclusions 


 Australia has the third largest ocean territory in the world, but we've only mapped 12 per cent of it. The RV Investigator is using state of the art equipment and design to map the sea floor.

Many locations being accessed by cruise ships and deeper draught cargo vessels are unlikely to be surveyed to full modern standards in the foreseeable future.
Navigators of these vessels therefore need to ensure that they fully appreciate the limitations of available hydrographic data and act accordingly.
More owners should perhaps consider installing forward looking sonars for vessels operating in Polar Regions and away from recognised routes elsewhere.
Such action might well have saved World Discoverer.
It should also have prevented the damage to Noble Hawk, which incurred significant salvage and repair costs as well as the associated loss of revenue”.

Links :

• GeoGarage blog : Digital map error may have led to minesweeper grounding / USS Guardian probe report evades key issues, raises more questions / Italy cruise ship Costa Concordia aground near Giglio / Map found to be erroneous in Sea Diamond case / End of Rocknes court case / 'Old charts may have grounded sub'
• Seamount catalog

NZ Linz update in the Marine GeoGarage

Coverage NZ Linz Marine GeoGarage layer

As our public viewer is not yet available
(currently under construction, upgrading to Google Maps API v3 as v2 is officially no more supported),
this info is primarily intended to our iPhone/iPad universal mobile application users
(Marine NZ on the App Store) 
and our B2B customers which use our nautical charts layers
in their own webmapping applications through our GeoGarage API.  

6 charts has been updated in the Marine GeoGarage

(Linz August update published 5 September 2014 (Updated to NTM Edition 17)

• NZ463 Approaches to Wellington
• NZ512 Cape Karikari to Cape Brett
• NZ615 Marlborough Sounds
• NZ5114 Doubtless Bay and Whangaroa Harbour
• NZ6153 Queen Charlotte Sound
• NZ6154 Tory Channel Entrance and Picton Harbour

Today NZ Linz charts (183 charts / 323 including sub-charts) are displayed in the Marine GeoGarage.

Note :  LINZ produces official nautical charts to aid safe navigation in New Zealand waters and certain areas of Antarctica and the South-West Pacific.

Using charts safely involves keeping them up-to-date using Notices to Mariners
Reporting a Hazard to Navigation - H Note :
Mariners are requested to advise the New Zealand Hydrographic Authority at LINZ of the discovery of new or suspected dangers to navigation, or shortcomings in charts or publications.