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Old 11-11-2014, 11:03   #1
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How to overlay a chart in OpenCPN using GE2KAP only

First, a little background: I'm not a geek. I don't know a script from a hole in the ground, and if anybody tells me to use the Windows Command Prompt I immediately turn to another post. Java is something I drink in the morning.

I've found a reasonable technique for putting charts into OpenCPN with a minimum number of steps and/or geeky user interfaces. It does involve using GE2KAP, which you can find elsewhere in this forum complete with downloading instructions. The downloading process was tedious for me, partly because there are one or two files that got caught by my virus detector and I had to figure out how to stop that from happening.

GE2KAP is a great program. I've used it a bunch of times to get imagery in OpenCPN to show me where rocks, shorelines, etc. really are. But beware! Even at high magnification (say, 1000 feet view) rocks and submerged objects may not be visible. Fortunately, we maintain a good lookout and narrowly avoided learning this lesson the hard way!

So suppose you have a chart that you believe is accurate, for example, from a cruising guide. The instructions below allow you to display it correctly in OpenCPN. They seem long because I've included every little step -- the process is actually quite straightforward.

Instructions for overlaying a chartlet in OpenCPN using Google Earth and GE2KAP

Get an image of the chartlet. In the case of a cruising guide, take a photo of the page. Be sure the camera lens is directly above the center of the chart and the camera is parallel to the chart surface.

If you like, use a program like Photoshop or GIMP to crop and refine the image. I find it useful to brighten the image and increase its contrast, to make the final OpenCPN display more readable. Save the image in a temporary directory or desktop. Any format -- .jpg, .bmp, etc., will do.

Go to Google Earth and locate the general area where you want the chartlet to show. Scale the screen image to roughly coincide with the chartlet boundaries no need to be precise. Go to View/Reset and reset both Tilt and Compass.

Select the Add Image Overlay tool on the GE toolbar. (Looks like two rectangles slightly offset from each other. If there is no toolbar, go to View and select Toolbar from the pull-down menu.) You will get a dialog window. Give the chart a name (e.g. localname_PM for a chart from Pacific Mexico) and browse to where you've saved the image. Don't hit OK. (If you do, you can get back to the dialog screen by checking Sidebar under View, right-clicking the overlay name in the sidebar and selecting Properties.)

Slide the Transparency control back and forth to get a level that allows you to align the chartlet image with the GE image. Grab any corner to scale the chartlet to the GE image, and grab the center to move it into position. (Hint: Use the corners rather than the cross-hair in the center. Align one corner and then the opposite one. Keep working it until you get it right.)

Select a transparency level high up on the scale toward Opaque. If you make the chartlet too transparent you won't be able to read things like depths and waypoint names; if you make it too opaque it will appear in OpenCPN with a black border around it, interrupting the flow of the other chart features. Now click OK. Go to View in the taskbar and unselect everything, to give you a clean image.

Open GE2KAP and create a chart exactly as you would have done for a GE image without the chartlet overlay (in other words, just use the left side of the interface, ignoring everything on the right). Note where GE2KAP files the chart in your directory structure (in my case, C:\GE2KAP\GE2KAP.V10.0.6.2\Charts).

Open OpenCPN, select Tools (image of a wrench)/Charts. If the directory you saved your chart to is already listed, select it and click Remove Selected. Now click Add Directory Browse to the directory where you saved the chart and click Done. Your new chart should now appear where it is supposed to be on the OpenCPN chart.

Good luck!
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Old 11-11-2014, 14:14   #2
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Re: How to overlay a chart in OpenCPN using GE2KAP only

AKKA - finally directions for a common man!!! thank you!
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Old 13-11-2014, 15:13   #3
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Re: How to overlay a chart in OpenCPN using GE2KAP only

Glad to help, Ed!

So I asked my wife to create a chart, following the instructions above. She's also not a geek, but boy, is she critical! Here are some minor problems she found in my post:

I should have “(GE)" after “Google Earth” the first time I mentioned that program. Later I use "GE" without explanation.

When I first mention the "transparency slider" I should have said "in the dialog window." My wife hunted all over the GE toolbar for it and became very frustrated at not finding it.

Finally, at the very bottom, "Browse to the directory where you saved the chart and click Done" is too brief. I should have said, "Browse to the directory where you saved the chart, click Open, then in the chart dialog window click OK."

Other than that, she did a great job and had fun, too!
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enc, opencpn

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