AvNav OCharts

Avnav Ocharts

=== not for Android ===


AvNav is able to handle charts in various raster formats. So far it was unable to handle any commercial charts. The  o-charts company supplies charts for various regions of the world for usage in OpenCPN.

After some agreements with o-charts, those charts can now also be used for AvNav (starting with version 20200515 with a plugin - see below). AT present you can use oesenc vector-charts.

To display those charts in AvNav they must be rendered into raster images. This is handled by a new plugin for AvNav(avnav-ocharts). The rendering takes place on the fly whenever tiles are to be displayed. However, major areas of the chart will be prerendered to cached tiles upon chart installation. This way those charts can be used the normal way - without worring about the rendering process.

All oeSENC charts handling is performed by the plugin - including installation (you cannot install them directly via the download page). For this purpose a dedicated GUI is offered by the plugin. You enter it from the main page via (User Apps) and  Ocharts-Provider  .

Buying and Installing the Charts

Important Hint: If you do not have a dongle from o-charts, your chart license is bound to your system. So in case of any trouble do not set up a new system (by writing an image to an SD card) but instead try to repair the system. If you set up a new system you will lose your license. I will by happy to support in case of trouble - contact e.g. via email.

To be able to buy charts at o-charts you have to create an account at their site first.

Afterwards you have to register the systems you would like to buy the charts for there. AvNav is using the "Offline" process .

This process consists of the following steps:

  1. Create a "fingerprint" for the system you would like to use the charts at. In AvNav you will create it in the GUI for the plugin and download from there.
  2. Upload the fingerprint to o-charts and create a system (basically assigning a name).
  3. Buy charts
  4. Assign charts to the system you created
  5. After a short time you will receive an email from o-charts with a download link (zip file).
  6. Upload charts to AvNav (via the plugin GUI).

For updates repeat steps 4, 5 and 6 (only requesting the notification mail at step 4)

For further chart sets steps 3-6.

For steps 2,3,4 and 5 you need a system with internet connectivity. You can e.g. use a laptop or an android device.

I created a video to demonstrate this process. Additionally here is a short description.

Hint: If the charts are already registered on the same system (for OpenCPN) you can directly continue at step 6. Alternatively you could also configure the OpenCPN chart directories with o-charts at the plugin .

1. Creating the fingerprint

Via -> you enter the GUI of the plugin, select the "Charts" tab.

Use "Get Fingerprint" to create the fingerprint file. If you are using an o-charts dongle - just select "Get Fingerprint(Dongle)".

Choose Download to save the created file on your device.

2. Uploading the fingerprints to o-charts

Enter the  o-charts page and upload the fingerprint.

With "Choose File" you select the file stored at step 2. Assign a meaningful name to the new system - this will be part of the mails you will receive later.

3. Buying the Charts

Select the desired charts from oeSENC charts.

4. Assigning to your System

At 1 you can assign charts to your system (in this screenshot this is not available anymore as the max amount of 2 systems are already assigned). At 2 you request the mail holding the download link (you would do the same for updates - in the screenshot: last version I have downloaded is 21, latest available is 23)

5. Downloading the Charts

After a short time you will receive a mail containing the download link for your charts. Download the zip file.

6. Uploading the Zip File to AvNav

In the plugin's GUI select "Upload Zip" to transfer the zip file downloaded in step 5 to AvNav.

There will be a progress bar during upload.

After the upload is completed the zip file will be unpacked. Some initial checks can take some time.

Unless configured otherwise, the charts will be uploaded to /home/pi/avnav/data/ocharts/charts.

After all checks have passed successfully, the dialog will ask to restart the plugin to make the charts usable.

If the newly uploaded chart contains updates to an already existing set, the existing set will be deactivated at restart. You may change this later on within the GUI. Chart sets not required anymore can be deleted.

During restart a couple of error messages will be displayed briefly but within 30s the status should be at least set to yellow (the plugin is now reading all charts).

After all charts are successfully read the status should change to green (READY).

If the status turns to "ERROR" (red) you maybe uploaded a zip that was not built for your current system. You can check details in the log file at /home/pi/avnav/data/ocharts/provider.log.

Now the charts are available and can be used.
At the "Status" tab you can see some more details.

In the screenshot you see the process ("FILLING") that was started after upload. It pre-renders a major set of chart tiles to a cache file. This will help to reduce on-the-fly rendering lags that otherwise would (potentially) occur due to the limited resources of the pi. This process can be active for several hours. The provider will use one CPU (out of the 4 available) on a raspberry pi during this time. Once prefill is completed cpu usage will dramatically decrease.

In any case you may immediately start using the charts (the prefill will only use the idle time).

As already mentioned, there is a chance of lagging to occur when you are displaying a particular range/zoom of the chart for first time (you will notice this especially on the smaller/older pi's). After first usage of an area the necessary tiles will be held in the cache file and there should be no more lag.

Adapting the Look and Feel

As the o-charts are vector charts you can adjust their look and feel. However some limitations must be considered:

  1. The modifications apply to the server's chart settings - so they will become effective for all displays.
  2. If you change the look and feel all data in the cache have to be wiped and all chart tiles must be rendered from scratch. So this will (potentially) again induce lag on smaller/older systems. The automatic cache prefill process starts again to pre-render a lot of tiles.

Changing display parameters is done in the plugin GUI(->), tab "Main Settings".

If you change a setting (1) it will be displayed bold. Changes will only become effective when you click "Update Settings"(2).

By selecting "Cancel" you can revert your changes. "Defaults" will reset to the built-in defaults. Most parameters are similar to the ones you find at  OpenCPN settings.

The following parameters are available.

Name Meaning Default
Show Text show text for chart objects true
Important Text Only hide less important text false
Light Descriptions show descriptions for lights true
Extended Light Sectors show sectors for lights true
Show Depth show soundings true
Chart Information Objects show special chart object infos true
Buoy/Light Labels show labels for buoys and lights true
National text on chart show national text true
Show Lights show lights true
Reduced Detail at Small Scale reduce details at lower zoom levels true
De-Cluttered Text improve text positioning true
Display Category Base, Standard, All, User Standard All
Graphics Style Paper Chart, Simplified Paper Chart
Boundaries Plain, Symbolized Plain
Colors 4Color, 2 Color 4 Color
Text Font Size Scaling for text on charts 1 (ca. 12px)
Soundings Font Size Scaling for soundings (since oesenc-pi 4.2.x) 1 (ca. 12px)
Scale Base scaling. Higher values for more details on lower zoom levels 2
UnderZoom Number of zoom levels to downscale higher resolution chart tiles if no chart tile is available at the requested zoom level. 1
OverZoom Number of zoom levels to upscale a lower resolution chart tile if is no chart tile is available with better resolution.
Hint: Scale, UnderZoom and OverZoom heavily influence the cost of the rendering process as they determine the number of charts to be processed to generate a single chart tile. Lower values normally mean less charts (i.e. being faster) - but there could be white areas between chart tiles. The defaults should be a good compromise.
Depth Unit for soundings(Meters, Feet, Fathoms) Meters
Shallow Depth Adjust to your needs 2
Safety Depth Adjust to your needs 3
Deep Depth Adjust to your needs 6

At the tab "Detail Settings" you can switch on/off particular chart features.

Feature Info (Object Query)

Since version 20201219 (versions of AvNav and plugin are required) chart object information is displayed upon click.

The dialog box displays compact information about "important" objects like lights, buoys and others.

By clicking "Info" you can view the raw information from the chart.


If you are running an AvNav image you can install the new plugin as package. For the Headless Images the necessary packages are already contained in the images. Additionally they are available in the repository. You need to install

  • avnav-ocharts-plugin
  • avnav-oesenc

For avnav-ocharts-provider you need at least version 20200606. The package avnav-oesenc is the oesenc-pi plugin - repackaged to install into /usr/lib/avnav/plugins/ocharts to avoid conflicts with a parallel OpenCPN installation.

sudo apt-get update
sudo apt-get install avnav-ocharts-plugin avnav-oesenc
sudo systemctl restart avnav

If you are working on other images you should add the repository from free-x:

deb https://www.free-x.de/debian buster main contrib non-free

You can also see the packages in the release list below. To use one of those packages (if it is not in the repo yet or if you need an older one) - just download and install the package (replace the version by the one you want):

cd /home/pi/avnav
wget -O avnav-ocharts-plugin_20200606-raspbian-buster_armhf.deb https://www.wellenvogel.net/software/avnav/downloads/release-ochartsplugin/20200606/avnav-ocharts-plugin_20200606-raspbian-buster_armhf.deb
sudo dpkg -i /home/pi/avnav/avnav-ocharts-plugin_20200606-raspbian-buster_armhf.deb
sudo systemctl restart avnav

You can also download to a PC, transfer by scp/WinScp to the pi and install then.


You can find all releases and intermediate developer builds (daily builds) at:

Release Versions

  • 20210328 packages
    • Parameter handling in AvNav (requires AvNav >= 20210322)
    • Limit for zip file size enlarged to 3GB
    • restart error fixed
  • 20210115 package
    • shift to python3 (requires AvNav since 20210115)
    • improved error handling for charts
  • 20201219 package
    • Display of object information (requires AvNav >= 20201219)
  • 2020115 package
    • Improved memory handling. The Xvfb will be restarted if it reaches 120MB
    • Faster start up. The chart information will be kept in a cache file. So reading the charts is only necessary if some charts have changed.
    • Removed memory leak within the used OpenCPN plugin (workaround) - so the memory usage of Xvfb will not increase that much any more.
    • Hint: When installing with dpkg -i (will give an error) you need to install missing dependencies with:
      sudo apt-get install -f
  • 20200710 package
    • You can now set the directory for the charts - see details
    • When uploading charts it is checked if those charts can be read. Otherwise the upload is rejected.
    • No errors in GUI any more when restarting the provider
    • correctly work on a vfat partition (as used by avnav touch)
  • 20200705 package
    • correct a problem in the OpenCPN plugin that could potentially stop it from decoding charts after running for a long time.
  • 20200606 package
    • first version

License Notes

Using the charts in AvNav with the oesenc-pi plugin has been agreed with o-charts and therefore is inline with their license conditions.
You have to agree to the license conditions of o-charts. Especially it is not allowed to copy the charts or use them on other than the licensed systems.

Access to the charts in AvNav is only possible from within the local net. You can connect at most 5 devices (Clients) at the same time.

For software licenses see the Readme.

Technical Details

The charts are provided by an executable on the raspberry pi that normally serves at port 8082. This executable loads the oesenc-pi OpenCPN plugin.
Communication with AvNav is handled by an AvNav plugin.

The GUI is a reactjs app that is also provided by the executable. It is integrated into AvNav as a User App.

You will find the complete code at GitHub.

You install into /usr/lib/avnav/plugins/ocharts. The data directory is /home/pi/avnav/data/ocharts. You can reconfigure the AvNav plugin by editing avnav_server.xml. Normally this is not necessary at all. If you need to configure anyway this has to be done in the Plugin-Handler section.

<system-ocharts port="8082".../>

For a list of available options refer to the description in the plugin source code.

If you e.g. want to use charts that you already installed for OpenCPN you can just point to the OpenCPN o-chart directories:

<system-ocharts chartdir="/my/chartdir1,/my/chartdir2"/>

Normally it is recommended to upload the zip files as described at  charts .

Since version 20200709 you can separately set the directory for uploading the charts:

<system-ocharts uploadDir="$DATADIR/charts/ocharts"/>

In this example the directory is set to /home/pi/avnav/data/charts/ocharts (normally it is located at /home/pi/avnav/data/ocharts/charts). This could be helpful on the  touch image as sufficient disk space is available only in /home/pi/avnav/data/charts.