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Updating charts is a bit of a mess

Globally the whole business of updating charts is in a bit of a mess at the moment and probably will be for a while. Most national hydrographic offices are fairly well set up for maintaining their paper portfolios. This is no great surprise as some of them have been in this business for a century or more. However with the advent of electronic charts a lot of things have to change. The whole production process needs to be reorganized (not cheap) and some of the basic ways of thinking about charts have to change.

Raster charts are commonly produced as facsimiles of the paper charts. In a simplistic system they are literally scanned from the paper originals. This can give rise to inaccuracies for a range of reasons not least of which are distortions in the paper and non-linearity in the scanner. Scanning at a resolution appropriate to the electronic chart can cause a rather jagged appearance which is most noticeable in diagonal lines and known as aliasing. The raster chart has far fewer dots (pixels) than the corresponding paper chart and this can compromise appearance. A better production method is to create the raster image from the same electronic chart images used to drive the paper printing process. There are still some issues here with re-projection which need to be handled correctly but in general this is a cleaner and more accurate process. It also allows image processing such as anti-aliasing which gives a better visual impression when the electronic chart is displayed.

In either production technique the updating of the raster charts follows on more or less naturally from the time served paper chart update process. It is then common for the vector charts to be produced from the raster data, more or less indirectly from the paper chart production mechanism. At the end of the update chain are the third party chart producers who copy the official data sets and repackage them in a variety of ways. Quite naturally these are the last types of charts to get updated.

But this is all changing because this is not a good way to handle vector data and vector data is the future. It is a separate issue as to why vector charts are the future or whether it is the right future but for now it definitely is the future. The IHO and other august bodies are committed to this and substantial funds are being invested. This matters because creating vector data from paper charts is just not a good way of doing things.

In the vector world everything is an ‘object’ like a light or a depth contour or a traffic lane. Each object has ‘attributes’ like the color red or a certain depth. Each object also has a position (the ‘vector’) so it is represented as a point, a line or an area. These objects can be quite readily managed in a simple database but the natural way of organizing them is to tie them more directly to the raw survey data. So when a report is received that a new wreck has been found it is just entered into the database – no intervening chart required.

Vector charts are now a cinch to produce. A cell is just a collection of all the objects in a given geographical area. The problem of actually displaying the chart data is palmed off to the ECDIS or ECS. Paper charts and raster charts are a bit more problematical because the traditional role of the cartographer has been taken out of the loop. Have you ever wondered why a modern chart display simply just does not look as good as a paper chart? Well this is why, there is no longer a cartographer involved to lay out the chart and make it look ‘just so’. Instead we have a dumb computer, and they are all dumb, attempting to reproduce the sort of work that takes a human many years of training and experience. It just doesn’t work so well.

Now to be fair the automated vector to raster production processes are getting better but none the less there is still a complete role reversal. The raster chart becomes a second class citizen to the vector chart and the paper chart ends up at the bottom of the pile. Instead of being the primary focus for updates it becomes the last. There are undoubtedly many advantages with vector charts and with paper charts generated from vector databases. However, for the foreseeable future, they are never going to match the visual quality of the charts that have become standard fare for the mariner for many years.

Last in the chain will always be the third party chart producers. Fortunately as their update feeds become predominantly more electronic (just another output from the database) then these updates should become more timely. Ultimately they should be able to match the official charts for accuracy.

Just now we are in a great transition phase. Some hydrographic offices are pushing ahead with vector only systems while others just deal with traditional paper charts. Most are somewhere in between and possibly a bit unsure of which way to go or how it is all going to shake out. Meanwhile the mariners can look forward to improved electronic charts coverage and more rapid updating. They can also anticipate charts which do not look so good and which, in some cases, are going to cost more. Maybe this is just a classic engineering compromise.


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