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Old 16-08-2009, 10:59   #16
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cm93 thoughts

Hi,

Regarding the comment about not trusting cm93 unless you have a source to compare to...

I'm fairly convinced that cm93 data is a faithful reproduction of the data provided by the various national hydrography agencies that provide the data. The folks at cmap don't do surveys: they license, repackage, and resell data. I think a more legitimate concern is whether not mistakes were made in the making of the vector charts. But I have compared CM93 to 'source' data from canada, usa, and australia and never seen a dicrepancy. I have seen disagreement between cm93 dataums and the datum on mexican charts, but i don't know who made the mexican charts i was comparing. One charts said US Navy surveys from 1900, so lord knows what datum was used. I have also heard about bad chart datums around the philipenes, but the fellow who told me about that also told me the 2009 release fixes them.

So to me, the issuse about cm93 quality in low traffic/remote areas is really just the same as the fact that there are NO good charts of these same areas because no one has ever surveyed them. Generally, and not withstanding the areas missing in these myterious latest releases, if good charts of an area exist, Cm93 includes them.

As for the latest releases, lets here more about the navionics charts 'missing' the same areas as the new cm93? Can the author of that post provide a scpefic example? Could the 'missing' charts the intentional removal of charts that were not good quality?
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Old 16-08-2009, 11:18   #17
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Originally Posted by sae140 View Post
That of course begs the question of what constitutes a reliable source ?
Many would say 'British Admiralty charts' without a moment's hesitation - but even these were originally drawn up by the use of lead line soundings back in the days of sail. Only those areas used by commercial traffic have since been surveyed by modern methods - and even then some obstacles have been missed.
The UK coastline is one of the most intensively surveyed in the world, yet there was an interesting case on British TV recently in one episode of a series called 'Coast', in which a heavily-laden vessel had briefly grounded in a channel which should have been clear for heavy shipping. A survey vessel was duly dispatched and an underwater ridge was identified, with one previously unknown peak rising very close to MLWS. There was nothing marked on the paper charts, so therefore nothing on any of the electronic charts based on them.

I would say CM93, along with other electronic and paper charts can pretty much be trusted by shallow-draft leisure vessels in those areas frequented by commercial traffic.
Charts (of any kind) for off-the-beat places, like south sea islands and indeed anywhere where coral heads grow, should be treated with a huge margin of distrust. You may be using modern charts and equipment, but the surveys on which the chart data has been based may be a century or more old, and all sorts of hazards might have been missed.
I could have been more precise about the word "reliable", but then we are not talking about the general reliability, or lack thereof, of charts and the surveys the are based on. For "reliable source" read " as reliable as possible" . When it comes to what this means in reality, you are off course right in what you are writing. For offshore areas I generally prefer the international chart series in scale 1:3.500.000, for navigation.

Quote:
I would say CM93, along with other electronic and paper charts can pretty much be trusted by shallow-draft leisure vessels in those areas frequented by commercial traffic.
Conway Reef is not a reef in an obscure South Sea area. It is situated close to the routes between Vanuatu and Fiji to/from New Zealand. Also on the route between Noumea and Nukualofa (New Caledonia to Tonga). So it is very much an ongoing concern both for commercial shipping and cruisers.

My main point is the lack of B-scale or lager scale coverage for many offshore areas in CM93. I do hope the exist, and that I somehow just don't have them.



Conway Reef - Wikipedia, the free encyclopedia





Thomas
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Old 16-08-2009, 16:14   #18
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Conway reef

Hi all;

I did a little investigation on Conway reef, aka Cevi-I-Ra.

First of all, it is indeed in an area that has has been surveyed to a higher level of detail than we get in CM93. See figure 1, which is a New Zealand raster chart. The red mark is on the reef ( at least I think it is....never been there).

The next picture is the same red mark on the same location showing CM93 detail for the area. We don't get told much, but there is a name and a small black dot. Pretty crummy coverage of a reef with wrecks on it, if you ask me.

One way or another this area is missing in CM93. Is it one of the infamous 'missing' files or if it was left out because someone thought the coverage provided was adequate? Who knows. Thats why we started this forum!

Figure 3 shows that the only coverage for this area is at level A, where as most the rest of that area, even open ocean, seems to be covered at level B or better. See Picture 1. The cross hatched areas all have higher detail coverage.

Also, Ceva-I-Ra and Conway reef are the same thing, but google earth can't make up its mind where it is. See figure 4.

All in all, I think the only thing to say here is thanks to Cagney for pointing this out to all of us.

Any one else have similar observations?
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Old 16-08-2009, 19:06   #19
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Originally Posted by dacust View Post
I think you got your comparison backwards. Ever tried to open an old spreadsheet with newer software? It almost always works.

I could see that an old version of nav software might not be able to display newer charts, but would not find it surprising at all that it could read older charts just fine.

-dan
Is not CMAPECS 4 from around 2002?
The CM93 from 2009 reported to crash it.
Maybe I got it wrong, but I though that was the complain.


I am almost 60 and was a great sponsor to Mr. Gates for a lifetime and I have plenty of old files I can not read any more despite they are all created with his software. The worst have been "Works" files, 2 issues later and no way, got to keep the old software and an old PC because converting every file was just a to expensive task. Surprisingly, the earlier versions of Open Office could read them.
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Old 16-08-2009, 20:35   #20
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Sorry, I see what you mean, now. I was think of fairly recent stuff. I can see where really old files might not be supported. Seems like they should, though.

But it's understandable that an old version of CMAPECS could have a problem with newer files.

-dan
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Old 17-08-2009, 10:46   #21
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Two more observations while we are in this area. Matthew Island 190 miles and Hunter Island 145 miles WSW of Conway Reef are shown correctly in B-scale on my cm93 chart from 2001.

Look at the third picture in GDD:s post above. Notice the underwater ridge pointing south from the eastern part of Fiji.
Under the Label "Lau Basin" you can read "Ha'apai Group".
Everyone who has cruised this area knows of course that Ha'apai is the name of the "middle" group of islands in Tonga, and has nothing to do with Fiji. Sloppy editing like this makes you wonder what's going on.

I think it was a huge step forward when OpenCPN was able to display CM93. It's a very good general reference and planning tool and quite good in many areas. Just be aware of the weaknesses.....

Thomas
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Old 17-08-2009, 14:30   #22
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cm93 missing areas

Cagney,

Are you saying in this quote that there used to be B scale coverage of the area SW of Conway reef , but now that coverage is gone?

"Two more observations while we are in this area. Matthew Island 190 miles and Hunter Island 145 miles WSW of Conway Reef are shown correctly in B-scale on my cm93 chart from 2001."

If so, that can be added to the list of places that have gone missing.

My list ( by memory) is

1. Desolation Sound in BC Canada in D or E scale, shown in 2006
2.West Coast of Mexico south of Baja in C scale, shown in 2006
3.Center of the North Atlantic in B scale, shown in 2006
4.Areas described by Cagney between Fiji and NZ in B scale, shown in 2001.

A list like this is really what I was hoping for when suggesting this forum. Additions most welcome!

George
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Old 17-08-2009, 15:03   #23
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Quote:
Are you saying in this quote that there used to be B scale coverage of the area SW of Conway reef , but now that coverage is gone?
No, I'm just pointing out that just less than 150 miles west of Conway Reef the B scale coverage exists, in an area with similar dangers to navigation.
Note that my experience of different editions of cm93/2 is limited.
Thomas
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Old 18-08-2009, 00:12   #24
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Originally Posted by GDD View Post
Cagney,

My list ( by memory) is

1. Desolation Sound in BC Canada in D or E scale, shown in 2006
2.West Coast of Mexico south of Baja in C scale, shown in 2006
3.Center of the North Atlantic in B scale, shown in 2006
4.Areas described by Cagney between Fiji and NZ in B scale, shown in 2001.

George
All,

I suppose we are still talking here about the cm93 ed2, officially not supported by c-map.
However, is the same information also missing in the 2008 or 2009 version of cm93 ed3?

Klaas
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Old 18-08-2009, 01:49   #25
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Would be great to know about others with electronic charts, whether Conway shows up or not. Very alarming to know whole islands are missing. I checked the 2004 ed. (this particular cell is of 2000 though), Conway is not there too. Now I wonder if Conway was on CMap charts any time. Maybe the Chinese fisher stranded there 2008 used CMap too?

Btw. My CM93/09 shows level Z,A(1:3000000),B(1:1000000) & C(1:200000) at Conway, are there different CM93/09 floating around?

I was eyeball searching for some hours, but compared to Navionics from Phuket to the Philippines I did not find a missing rock - no warranty for that, my eyes are old.

Coron Bay, there is data missing compared to 2004, but in the Navionics too and it is greyed out, so you know, you have no data.

I found plenty of other mistakes, even in the newest ENC (China Sea from Singapore), Lights keep comming and going, light sectors change as you change scale, sea where there is land since 5 years (new container port operating since 2 years in Subic Bay), but nothing so dangerous as compared to Conway Reef!

Does anyone know why Google Earth is hiding so many reefs and small islands? they have been there in older versions (Scarborough for instance), but now only a blue spot. Looks like the chart producers are after that...
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Old 18-08-2009, 07:57   #26
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Would be great to know about others with electronic charts, whether Conway shows up or not. Very alarming to know whole islands are missing. I checked the 2004 ed. (this particular cell is of 2000 though), Conway is not there too. Now I wonder if Conway was on CMap charts any time. Maybe the Chinese fisher stranded there 2008 used CMap too?
Hi Blubaju,

I checked for Cevi-I-Ra / Conway on a borrowed Garmin Bluechart Pacific 9.5 map and it's clearly there, complete with sandy patch, 3 wrecks and a lot of rocks around it. Survey 1975, scale 1: 25000 or so.
I did the same exercise on the Nobel WF22 maps, they show only an indication of some obstructions, no name.
My 2002 edition of CM93 shows on the spot where Conway is supposed to be the blue outlines of a square, tilted 45 degrees. There are some more geometric figures in the neighborhood. Could this be a c-map notation of "better stay away"?

Klaas
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Old 20-08-2009, 06:41   #27
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I concur with Thomas - on the 2008 and 2 different 2009 CM93/2 folios I have, B-level coverage exists at the surrounding areas of Viti Levu, Vanuatu, Noumea and Tonga Ridge. However, Hunter Ridge (including Cev-I-Ra) only has A-level coverage. I've attached a graphic showing the area. (B-level areas are hashed)
Whether charts cells are missing or were never created, couldn't say.

I've bit-compared the relevant A-cell (01500480/01500480.A) common to these 3 x folios, and they're identical.

BTW, the 1998 folio I have doesn't show Cev-I-Ra/ Conway by name, but simply displays a small circular 1000 metre contour at that location.

If ever there was a case for creating a user overlay system to display updated information, this must be it.
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Old 06-03-2011, 16:58   #28
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Re: CM93 Issues

I think to be fair, a distinction needs to be drawn between developments close to land -where caution needs to be exercised anyway - and uncharted islands or other lumps of rock in mid-ocean.

In my home waters, the North Sea, an almost continuous development of off-shore windfarms is taking place and these, together with frequent oil platform movements, renders even the latest admiralty charts out-of-date just as soon as they are printed.
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Old 06-03-2011, 17:17   #29
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Re: CM93 Issues

I've been thinking of crowd-sourced data for a while, following a few marine related projects. So far all are relatively modest.

A largest crowd-sourced mapping project is probably Wikimapia. I think it's also a good example of why the approach is very difficult to get right. It's fun to browse but pretty useless for practical purposes, and certainly not useful (borderline dangerous) for anything navigation related (except for Google maps, underlying it, of course) It contains large amount of data that is simply incorrect, lots of fake data, data that's entered carelessly (so its not really wrong but isn't quite good enough to be "right"), various spam (as any other crowd based system) etc.

In marine environment, from various online discussions I also get a feeling that many people in boats don't have any better idea of their surroundings. They'll run aground where ground is properly charted, but will consistently claim to be "in deep water/mid channel" etc and claim various uncharted rocks and shoals.

Granted, this would likely result in many "phantom" hazards charted, rather than less - but chart data that "cries wolf" is just as useless as the one with omissions.

So, to be successful, crowd-sourced system needs to have a significant amount of 3rd-party, preferably professional review. But even that's not a guarantee of data quality. Consider that Google does an overlay of their professionally sourced chart data with POI information they derive from their search data. I often find that the overlay information tends to be wrong, despite their best efforts. (As an aside, my favorite is Little Palm Island in Fl. Keys being marked as "Fishermans Hospital Therapy" ).

Just my 5 cents.
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Old 08-03-2011, 05:26   #30
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Re: CM93 Issues

Hi,

The Conway Reef (Ceva-I-Ra in Fijian) with NZ charts :
Marine GeoGarage

Peter
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