(Revised 18 Mar 2012) Creating a KAP chart overlaid with GE image (using OpenCPN and GE2KAP) 

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The purpose of this procedure is to create a KAP chart of an area displayed on the OpenCPN screen with an overlaid image from Google Earth (GE) that has transparency set such that the screen display (with depths and other information) shows through the GE image.

I will assume you have installed the GE2KAP program but have not used it for this purpose.


1. On your computer, wherever you choose, create a folder to contain the charts you will create.  I use the following:

2. You need to prepare both the OpenCPN and Google Earth (GE) programs.

a.  OpenCPN: 

On the Toolbox/Etc. page select the Lat/Long settings you want to use. In this case I have selected 'Decimal Degrees'.  It doesn't matter which you select.


 Click 'OK' and return to OpenCPN and display the area from which you want to create the overlaid KAP chart.  For example, using a cm93 chart of Port Binanga.  (NOTE: It is also possible to use raster scan charts (BSB/KAP) as described here)

b.  Google Earth

Start the GE program and go to the Options page.  If not already done so, uncheck the box 'Show terrain'. Though not necessary you can select the same parameter for showing Lat/Long as you did in the OpenCPN program,  i.e. in this case Decimal Degrees.    NOTE: Your version of GE may have these parameters on another page ... hunt them down.

On the GE screen uncheck the boxes in Layers and My Places.  Check the line Temporary Places.  When you close GE2KAP and the GE program you can select to Discard the temporary places. Doing this each time you run this procedure will allow you to discard the locations you have been to and prevent a build up of unnecessary locations in the GE program. 

In the View window uncheck all of the listed items.  (See OPTION below)

OPTION:  Although you can do this later, now is a good time to allow GE to display historical imagery that may be better than the most recent imagery.  To do this select View/Historical Imagery.


Launch the GE2KAP program. The program should display the GE window with the historical imagery slider in the upper left hand corner.

Now begin to fill in the GE2KAP program entries.  (This is being created with a pre-release version.  Yours should be later than version 8.1.3)

In 'Chart Location/Name:' enter the path to the folder you created earlier followed by a name for the chart you will create.  Don't forget the backslash '\' at the end of the folder.  Subsequent launches of the program should have the folder location already filled in.  In 'Overlay KAP Chart/Image file or OpenCPN'  enter 'opencpn'. 

If you want the land to be a transparent area of the chart  check "Make land transparent" and set the threshold from 10-15 %

 See Land Transparency.below for examples.

Continuing with entries above, in the 'Depth Units:' window enter the units that you have selected for depth in the OpenCPN program.  In this case I am using 'Feet' which is a setting I have made in the OpenCPN program under Vector Charts with the choices of feet, meters or fathoms.  Whichever you have selected the OpenCPN display will show what it is.

When entries are completed click on 'Create Chart'  Note that the bottom three boxes are unchecked.  The program will now go into a 'learning' phase to identify characters on the display.  As a character is highlighted in the window 'Cursor Image Data', enter the correct character. See below.  In the first screen below, I have already entered the characters 'Cursor' and the next one to be entered will be the colon ':'  Continue entering characters.  In the second screen below the figure '7' is being entered.  When the program has learned sufficient characters it will continue processing.  On subsequent uses of the program it may need to have more characters displayed in which case this screen will appear again. 


But you can't read those characters in the 'Cursor Image Data' box?

Go to Settings/Display/Appearance/Effects. In the box 'Use the following method to smooth edges of screen fonts:' change the setting from 'Clear Type' to 'Standard' as shown below.  Click 'OK' then 'Apply'.

NOTE:  If in the future you change the Lat/Long settings in OpenCPN to another parameter, such as Degrees, Decimal minutes, don't worry.  When you run GE2KAP it will present you with screens to identify the NEWS characters such as below:


Continuing ...

NOTE: Do not move  the mouse while GE2KAP moves the cursor to the four corners of the OpenCPN window. 

DON'T TOUCH ANYTHING until you see the following:

Move the window down to where the Transparency slider is visible.  Move the slider to the left to display the GE screen.

Note how dark it is in this case.  Is there earlier imagery that is better?  Moving the slider to an earlier time shows that there is, indeed, a better picture.  Why?  Who knows besides Google!

The GE image is displayed with the size of the OpenCPN window.  However, you might want to 'play' with the image.  Use the '+' and '-' keys to zoom in and out for the chart you want to save.  Use the 'Transparency' slider to create the amount of overlaid transparency you want.  If the images don't align properly, you can do that by clicking on the green cross and moving the chart image to coincide with the GE image.  You can zoom in to a smaller view if desired.  Whatever is display in the GE window is what the chart will look like when it has been processed.

NOTE: Because we used the Historical Imagery feature of GE to find the best chart, we are stuck with the display of the Historical Imagery slider in the upper left hand corner.  Oh well, it isn't a perfect world.  However, if, previously, we could not find a better chart, the slider could be eliminated by clicking on the 'X' in the slider window.

Once you have the image/chart you want, raise the window and click on 'OK'

Again, DON'T TOUCH ANYTHING until you see the following:

If you want a preview of the finished chart, click on 'View Chart' to get:

Looks OK so now launch the OpenCPN program, go to Toolbox/Charts. Highlight the folder created previously and click on 'Add Selection'.  Then click on 'OK'.

If not done previously, it's useful to select 'Show Chart Outlines'.

Now click on the KAP chart. It's the blue bottom button and is outlined in red.

And the result ...

Land Transparency

The transparency of the land can be changed by the selection mentioned above.

As an example, in this case the land was not selected to be made transparent.  The image was adjusted to show the reefs.

The same image with the land made transparent (10% for this example).  No GE detail is shown on the chart water area.

Examples from Paul Higgins, our devoted developer of the GE2KAP program:  First with Land Transparency off.

and then with Land Transparency turned on.

Return to continuing entries

Using BSB/KAP charts

If you have some raster scan (BSB/KAP) charts loaded the same procedure can be used to create the GE overlaid on the chart.

First load the raster scan chart folder into OpenCPN.  Navigate to the place desired.  Here is an example:

Running the GE2KAP program the following is displayed.  (Note that the depths are displayed in fathoms, which was entered in the GE2KAP program)

The image is corrected in location to:

After zooming in the chart was saved.  The area to the NE was missing so it was displayed for another chart.

After loading the charts into the OpenCPN program the following is the result.  Note that the entrance through the reef is easier to see.

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