Cm93 Charts Download Free
Madeleine Harrier
"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.
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.
I have charts in .BSB file format that I would very much like to use on locus for the same reasons stated above. All NOAA charts are available in .BSB so I can`t be the only one who would love to see this ability in locus. Thanks.
Some cells have built in corrections already applied. The values wgsox and wgsoy, are offsets to bring the original chart cell to WGS84. See the first and third cell in the picture above. The values are for information only, and cannot be changed. These corrections are generally correct, but not always. Sometimes the corrections are wrong and sometimes there are no corrections where there ought to be. This is where this manual offset feature comes in handy.
In order to use this feature effectively, one needs a geographically known reference point. As an example, say there is a NAVAID present on the chart cell with known WGS84 lat & long, as from a light list. In this case, one can drop a waypoint on the chart, edit the waypoint properties to the known lat/lon, and then use the CM93 Offset Dialog to slew the cell/MCOVR so that the dropped waypoint coincides with the NAVAID feature on the cm93 cell (chart).
You may also use a geographical feature such as a Cape or point whose location is absolutely known, as by reference to observation, or by rendering on another, more accurate chart such as a trusted scanned raster chart or georeferenced photo chart.
Zooming out to next smaller scale chart makes the triangle mark jump NNE. Time for some corrections, as we, at least for the purpose of this example, are confident that the larger scale chart is correct.
What we do on Ocelot
We've been using OpenCPN since 2010 (when they added Chart Quilting) and are very happy with it. It is constantly under development so new features are being added by a dedicated team, many of whom are also cruisers. Features can be requested and all such requests are seriously considered. There are several active discussions on Cruisers Forum where features and/or problems are discussed and solved (the developers respond personally). New releases come out once or twice a year and since the software is "open source" all new versions are also free. In fact, you are free to download the source code and add new features yourself if you want to.
Unfortunately, Google has recently changed Google Earth so that it no longer works well with OpenCPN, so much of our Google discussions below no longer work. As of 2021, you can still use GE imagery, but via SAS Planet rather than the GE client, as described in our Making mbTiles page.
Raster Charts vs. Vector Charts:Electronic charts usually come as either Raster charts or Vector charts, and most navigation programs can use both types. But there are some significant differences and limitations with each chart type.
How to use GE when you're offline:
When you go to new places with GE, it has to download the information it displays from the Google servers. These are fairly large graphical files, so it can take some time, even with a broadband internet connection. GE displays a little circle in the lower right corner of the GE window, to show download progress. When the circle completes (and turns color) then you know that the download for a given view has completed, and you can move on to your next view. But to save time (and internet bandwidth) GE caches (saves) this received information on your computer. So going back to somewhere you've already been to displays very quickly, because the information is coming directly from your own hard drive.
So the trick to using GE offline is to use GE to visit those places that you want to go beforehand, while you have an internet connection. Then you save the GE cache files somewhere. When you cruise to those places, copy the cache files back so that GE can use them again.
WARNING: We have noticed that Google updates their database every few weeks. If you then let your GE client connect to its servers, the servers will notify the GE client to only use the new database. This causes the client to ignore any cache files from earlier databases! We find this hugely annoying, as it can take several hours to accumulate a few GE caches. Therefore, once we've accumulated several caches, we don't let our GE client contact its servers (or get on the internet) so it thinks our caches are still valid and it will continue to use them. If anyone has a better solution here, please contact us!
There are several ways to take a snapshot of a GE image and convert that snapshot into a KAP file. Our KAP Files page shows how to automate this process to produce groups of KAP files (KAPs) with minimal overlap. They can be programmed to follow a coastline, or to cover an area. KAPs have the advantage that you don't need the GE Plugin to display GE data, so they can be displayed on Mac and Unix computers as well as Windows computers (although they may need to be generated initially on a Windows computer). While they're usually too large to put on the internet (several GB) they're relatively easy to share with other cruisers you meet. In our opinion, gathering the GE data into the GE Cache and displaying that info with the GE Plugin is faster and easier, but more delicate (caches can be invalidated too easily) and they're not sharable. While we used to prefer using the GE cache and the GE plugin, we now tend to create KAP files, since the tools to automate this process are now much better, and the resulting KAPs are both stable and sharable.
Setting up to use the Google Earth Plugin:
You should only have to do this stuff once. It looks a bit complicated, but that's mainly because we're trying to explain everything as we go along. This actually happens pretty quickly and easily.
Saving Google Earth information:
You will want to do this for each place that you plan to cruise to where you'll want GE information. This looks complicated, but it really just breaks down to:
We have found that overlaying the GE window on top of charts doesn't work very well. Since the charts and GE are running at slightly different resolutions, they don't overlay exactly, which makes for a very confusing display. But feel free to play with it if you want. If you open the Toolbox and go to the PlugIns tab and select the GoogleEarth plugin, there's a Preferences button on the left. In there you can futz with the Floating Window Transparency slider until you can see both the GE info and the underlying chart depths. But since the 2 windows are not precisely aligned, this is of limited usefulness.
One way we've found is to use our radar, which is connected to our NMEA bus and therefore gets GPS positional information (our radar is an NMEA receiver, but not a transmitter). In order to use these methods, your radar must receive GPS information, and it must also receive orientation information (which way it's pointed) from a compass (usually the autopilot's fluxgate compass).
One method is to put our radar's cursor on a prominent landmark (like the tip of an island or peninsula), read off the lat/lon, and compare that to our electronic charts. Similar in concept is to put a waypoint on a prominent landmark, like the end of an island or peninsula. We've found that our radar displays waypoints on the screen, so that is another correlation between our charts and reality (as measured by radar). These methods are not super-accurate, but they'll give you a rough idea, which can be immensely reassuring when entering a new anchorage in the dark.
As of 2015 we've seen CM93 chart databases dated 2000, 2002, 2005, 2006, 2008, 2009 and 2010. All of them have noticeable differences over their predecessors, not always good. While we try to have the latest charts, some of the earlier chart databases had more detail in certain areas, although older charts tend to be less accurate. We also carry paper charts for wherever we go, despite having 4 computers on board, all with electronic navigation packages, and despite having 9 GPSs on board.
I see that there is support for S57 & S63 electronic navigation charts, but what about the frequently used C-MAP CM93 format? The version 2 format has been around for ages, and a format description can be found here:
The circa-2012, CM93 chart shows an outline of the Marinas in the Sabalo Estero, but with few details. Fortunately, the combination of our CMAP charts and the Blue Latitude Press Pacific Mexico guide gave us the information we needed.
The next question became how to use the information in the book. Obviously we can the anchorage guides and figure out where we would like to go. In addition to that we had good advice from Blue Zulu and other cruisers who has passed before us as to their favourites (and importantly why!) The cruising guide also has waypoints which I can enter into my existing navigation software and just bounce from waypoint to waypoint. And as I mentioned before, someone has been kind enough to scan in all the charts from The Panama Cruising guide (4th edition) and turn them into KAP files which can be read by some charting applications.
2017 was an unusual year for us, an entire year living on a boat in the sun. It has been an adventure and 2018 looks like it will be even more exciting as we move into the Pacific. Sadly also farther away from family.
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