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post #36 of Old 07-29-2011
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Originally Posted by brak View Post
While errors can happen anywhere, errors in NOAA electronic charts (vector or raster) are relatively rare and, more importantly, if there is an error in NOAA electronic chart - you can expect the same error in current paper chart.

At this point NOAA paper charts are generated from the same electronic data as those you download and use with navigation software. So while there is a benefit of redundancy with paper charts, there is no benefit of "better information" anymore.
Unfortunately, much as we might wish it were so, neither of these two statements is entirely true.

First, it is important to understand that NOAA raster charts (RNCs) are exact copies of the NOAA paper charts. In fact, they are produced by scanning the paper chart. Still, in July 2011, the paper charts are the basis from which raster charts are produced.

Next, there is at present no central electronic database from which either raster (RNCs) or vector charts (ENCs) are produced. Let me say that again, since there is so much misunderstanding on this point: there is no central database from which charts are now automatically produced.

To be absolutely sure of my understanding, I verified this today with two senior NOAA officers deeply involved in hydrographic cartography.

There is, in fact, a major effort underway to develop a central electronic database from which both RNC and ENC charts would be generated, but it is fully two years or more down the road before deployment. At present, RNCs and ENCs are produced by two separate offices within NOAA, though they collaborate closely in an attempt to avoid errors.

Potentially, of course, ENCs may contain many layers of information and these may be captured in a central database from which the charts could be produced. This is the goal, at least, if not the present reality.

Bottom line:

1. RNC (raster charts) are exact copies of the underlying paper charts. They are images of the paper more, no less.

2. Paper charts are the controlling "database" from which charts are produced at present.

3. At present, there is no underlying electronic database from which charts are automatically produced.

4. ENC (vector charts) are not necessarily identical to either the paper charts or their images (the raster charts). Therefore, they may contain errors of omission and of commission.

One thing I can agree with Brak about: NOAA charts -- both ENC and RNC -- are excellent products which NOAA takes great care in producing.

That these are available to us for downloading at any time, and free of charge, is a wonderful benefit we get from NOAA's hard work.

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