CM93 V2 marine vector charts

Hello

Locus could be a very good replacement for marine navigation software.

Almost everything is there:

- An excellent GPS handling

- Possibility to define and modify routes

Just marine charts import seem to be missing.

A lot of (most ?) sailors have a bunch of:

- BSB raster charts (versions 1 to 3, files with a .kap extension). As mentioned in a previous post, the description of the format is available on http://libbsb.sourceforge.net/bsb_fil....

- CM93 version 2 vector charts.

A description of the CM93v2 vector chart structure is copied below from the Open CPN site:

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CM93-version2 Charts has it`s own data structure consisting of a number of folders and files.

In the top CM93 directory is an empty file with the ".EXD", for example 20110803.EXD. The format is YYYYMMDD.EXD. This is the version, or edition, of the CM93 -v2 release.

The CM93 top directory contains a number of (144) subdirectories named from

"00300000" to "04501020", as well as six other files. These sub directories each cover a geographical area of 40° x 40° . The first four numbers describes the latitude and the last four, the longitude of the SW corner of the area covered.

The key to understanding the numbers is to realize that CM93`s coordinate system

of the world starts at the South Pole or to be exact at lat -90° long 0° and from there proceeds North a East with a factor of 3 for each degree of lat and long.

The tile 00300000 hence has the SW corner at lat from -90° + 0030:3 = -80° or 80°S to and longitude 0°E , and covers the area from 80°S latitude to 40°S and from 0° longitude to 40°E.

Looking at 04501020 it brakes down to lat -90° + 0450:3 = 60° and long 1020:3 = 340° subtracting 360° results in -20° or 20°W. So we have he SW corner at 60°N and 20°W .

One more example, the tile 03900840 has the SW corner at 40°N and 80°W.

Each of these sub-directories in turn contains directories with the individual charts. Ordered in scale from smallest to largest they are Z,A,B,C,D,E,F and G. Where Z contains overview charts and G contains harbor plans. Note that, generally, not all of these are present in each subdirectory.

Z covers 40° x 40° deg area and OpenCPN typically uses 1:3.000.000 scale

A covers 20° x 20° deg area and OpenCPN typically uses 1:1.000.000 scale

B covers 10° x 10° deg area and OpenCPN typically uses 1:200.000 scale

down to..

G covers 20` x 20` and OpenCPN typically uses 1:3500 scale.

The individual chart tiles in these directories have the same logic in the naming scheme as described above.