Wednesday, 18 July 2018

Using Satellite Overlay Charts in OpenCPN

Using Satellite overlay files to enhance your experience with OpenCPN.

How we make navigation safer using satellite image charts

While our travels progressed and we ventured to places favoured more by fishermen and cruisers than commercial marine traffic we began to see more and more chart abnormalities. The explanation behind the inaccuracies is that areas away from commercial ports and major shipping routes are less surveyed, commercial needs do clearly push for funding to create accurate charts. Also in a lot of the areas we were traveling the last hydrographic surveys were done well over a hundred years ago.  The Chart Datum based on Netherlands Government Surveys of 1904. 

This is last part of  two earlier posts dealing with OpenCPN. In the earlier posts I describe setting up Layers in OpenCPN on a Windows PC to display routes, tracks or waypoints. In the second I detail  getting an interactive Cruising Guide working using the embed links in OpenCPN waypoint descriptions in the Sail Malaysia Cruising Guide.  Also worth a read is our post about how we are Navigating In The Digital Age as well as a Chart Datum Overview.

For this demo I will use the zipped Malaysia Rev14 kap overlay files available from Terry **. I will use these files as they form part of a package for navigating in Malaysia. The zip file contains Google Earth kap files of the anchorage waypoints found in the Layers GPX file, and associated information available in the Cruising Guide.

** Keep in mind Terry updates these files as new information becomes available and he now has files for a very large area of Australia and SE Asia.     In December 22 the file revision for Malaysia is now up to Rev25 and all the charts are in mbtiles format with greater colour detail. 

This is reasonably easy to do:
Download the relevant kap overlay file
Create the relevant folder
Unzip the file into the folder
Direct OpenCPN to the correct folder
Test the outcome

Download the file containing the kap files, in this case   
Create a Folder called the name of the downloaded file or a name that makes sense to you. I use the MalaysiaRev14 when updates are available I can update the folder and change the name.
Unzip the files from the downloaded file into the directory and check the contents.

Direct OpenCpn chart manager to the new folder. Click apply then when the database has been updated click ok. Depending on the number of charts it can take a while for the update to take place.
After the chart manager is closed (if selected in the chart options) The borders of the new charts will be displayed on the active chart as seen here.

It is important to be at the right zoom level to display the new charts, zoom to a size where  the chart boarder fills or nearly fills the active chart area as seen here. Then switch between the charts using the buttons on the bottom of the page. Hovering on the button will display the origin of the chart folder in a pop up box.

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