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Computer Tips and Tricks
Computer Navigation
Last Updated: 05/28/2022

  Making Charts from Satellite Imagery Converting Maxsea Tracks and Waypoints
 to GPX for OpenCPN
  Google Earth Cache How We Navigate
Downloading the Charts we have already made
  Our Navigation Presentations

When we left the U.S. in 2007, the computer navigation systems were running in the $2,000-$5,000 range.  We just couldn't afford that, and especially not two of them (every long range cruisers needs critical equipment backups).  We also could not afford to keep buying map cartridges every time we moved a couple hundred miles--this is both a cost issue and an access issue. 

So our primary navigation system consisted of the following:

1.  A Garmin GPSMap 76Cx on the helm (with maps installed).  Link to current equivalent on Amazon
2.  A laptop down below on the nav station, with a NMEA connection to the Garmin, but also a USB backup GPS if we need it
3.  A 15" 12-v (cheapo) LCD monitor on a swing out arm in the companionway.
4.  A 'presentation mouse' to manipulate the computer from the helm station. Note, there are other much cheaper-appearing options on Amazon, however, most do NOT include an actual "mouse" function.  Most only have forward and back buttons, good for slide shows, but not for mouse movement on screen.  This device also has a 60 ft range.  Here's an alternative from Keyspan with a 100 ft range.

Our original navigation laptop in 2007 was an old (purchased second-hand) Dell laptop.  It was a several thousand dollar laptop when new, but we bought it 'refurbished' for about $200.  It doesn't need to be super-fast, and it didn't need much more than a 40-GB hard drive.  It was running Windows XP.

The first thing we did was strip almost ALL of the software off the computer.  We disabled the wifi, and took off the anti-virus and firewall, and made sure that NOTHING was being started by Windows at computer startup.  We also removed the 'user sign-in'.  So, turn this computer on, and it boots up immediately.

Then we carefully put ONLY navigation and 'underway' applications back on it:

  1. The OpenCPN navigation program

  2. GPSGate to help manage the GPS and Serial Ports for several navigation programs (optional)

  3. Airmail (properly configured for our underway communications functions)

  4. WXTide32 - Worldwide Tide Program (free)

  5. GPSU - For transforming GPS waypoints and downloading to Garmin (optional)

  6. A simple photo program of your choice (see ours)

This computer NEVER connects to the internet... so it doesn't need the anti-virus applications, Windows Updates, etc.

Making Charts from Satellite Imagery Using Sat2Chart (formerly GE2KAP)

See this info as a Powerpoint Slide Show (pdf)

Though the below information will tell you how simple it is to make a single chart, a more  comprehensive explanation of the newer "mbtile" chart-making process, and all the things you can do with Sat2Chart, SAS.Planet, and mbtiles, can be found here:

Website URL for contact info and new versions of Sat2Chart:

CruisersForum where Paul is answering questions and posting updates:

GE2KAP/Sat2Chart Facebook Group

Note:  In 2019, Paul renamed his GE2KAP program Sat2Chart.  Why?

1.  Google changed the interface to GoogleEarth so it is no longer possible for GE2KAP to capture the picture, georeference it, and save it as a chart file.  You can download an old version of GoogleEarth that DOES work, but using SAS.Planet is MUCH better.

2.  SAS.Planet is MUCH better for many reasons.  The biggest are: YOU manage your cache, not GoogleEarth (no disappearing data), SAS.Planet knows how to access at least 4 different satellite databases--if there is a cloud over your spot, you can easily switch views and check to see if another satellite database has a good view.

Important:  If you like GE2KAP/Sat2Chart and use it, you should go  right now and buy Paul Higgins a beer. He has spent a lot of time on this tool, and it is VERY useful to us yachties in remote places. Just think of how much money you have previously spent on charts and chart chips, and Paypal him $20.  (Look for the Paypal link under the picture on the home page.  You can pay with credit card, don't need Paypal account).

The primary program I use here is Sat2Chart. Sat2Chart will interface with either Google Earth or SAS.Planet, and take what is currently shown on your screen, and save it as a geo-referenced KAP file or mbtile. KAP files are 'raster' files and useable on most navigation programs, including:

Maxsea (but NOT TimeZero)
Coastal Explorer
Sea Clear

OpenCPN 5.0 can also access the newer graphic format of mbtiles.  mbtiles provide much superior detail/color rendition than KAP files.

The benefit of making chart files vs navigating IN Google Earth/SAS.Planet, is twofold...

1. You can use the built-for-navigating programs you are already familiar with, and make routes and waypoints, etc without learning yet another new tool.

2. Once you make a chart from Google Earth, it is there, no matter what happens to your Google Earth/SAS.Planet installation, or your satellite image cache file.

To use Sat2Chart, you need to do the following:

1. Have a compatible version of SAS.Planet installed (The current version of GoogleEarth doesn't work, if you insist on using GoogleEarth instead of SAS.Planet, download a working version here from Paul's download page).  You can download a version of SAS.Planet customized to work well with Sat2Chart from Paul's download page... just unzip to C:\ drive and create a shortcut on your desktop...only on Windows).

2. Either have your installation of Google Earth/SAS.Planet connected to the internet, or have the area you wish to make a map from cached on your computer. (see discussions on cacheing elsewhere)

3. Have the program ooRex installed on your computer.  Paul Higgins says to install the 32-bit version even if you are on a 64-bit Windows computer. Note that RexHide.exe has recently been causing a false positive virus notice on Windows Defender.

4. Have a subdirectory created to put the resulting charts (ie C:\Charts\SatCharts or something.

Note: On the original instructions (if you read the sailing forum Q&A, Page 1), there are also two other requirements that are no longer needed with the latest version. (ImageMagick and libbsb)

Once you have done all this, follow these directions:

1. Start up your SAS.Planet program and find the location you want to make a chart of. Whatever is shown on your SAS screen will go into the chart. You DO NOT have to be hooked to the internet. If using GE, if you have previously been on the internet and cached (saved by displaying when connected to the internet). GE will complain that it can't find the internet. Just tell it OK, and NO you don't want it to help diagnose your network problems. SAS doesn't complain.

2. If using GE, make sure your display in GE has NORTH straight up. For some reason my GE wants North at about 10 degrees (probably the tilt of the earth). You can quickly orient to North straight up by double-clicking on the 'N' in the navigation controls (normally in the upper right corner of the screen).   (Newer versions of GE2KAP automatically adjust this by default before capturing the picture).

3. If using GE, clear the junk/menu overlayed on the GoogleEarth screen (using the View menu). Anything displayed on the screen will go on the chart. So you want to turn off unnecessary GE layers and the Navigation--if possible get to just the GE picture.  (You cannot get rid of the GE logo).

4. Start up Sat2Chart as any normal program, from the shortcut on the desktop. If you have installed ooREX properly, it should just run. What you should see are 2 screens, one a black DOS-type screen which comes and goes, and one the user interface screen.

GE2KAP Screen

5. To make your first chart you need to do 2 things:

a. Enter or browse to the chart directory where the new chart will be placed, and include the filename. This goes in the Chart/Location name field.
Ignore the stuff in the lower half of the screen for now.

ie: C:\Charts\SatCharts\Tonga\NeiafuHarbor.kap

I think the folder you point to must already exist.  Note that Sat2Chart now has some excellent tutorials on getting started.  See the Help in the program.  It is well worth a few minutes to check the beginning help videos out.

b. Click the Create Chart Button. Voila, Sat2Chart shows some progess in the top window.  It is finished when it displays:

Successfully Created:
To View the output created press "View Chart"
To Calibrate another.. display the area on Google Earth.
Enter the name of the chart to create with its filespec below.
Then press the Create Chart button.

6. You can press the View Chart button, and it uses a simple graphic file viewer to display what just got created. I recommend that instead you load it into your favorite charting program and see how it looks.

Be cautious when first trying to navigate with a new chart.


More Details:

1. Check out the HELP button. It loads some nicely done HTML help which Paul has thoughtfully included in the zip file. (The button will try to load the help from a directory named Help in the same directory as GE2KAP.rex)  Paul has also done a great set of video tutorials, also accessible from the program (must have an internet connection for these).

2. The bigger screen (higher resolution) screen you have to display GE on, the more area one chart will cover at a given zoom level, AND the bigger the resulting chart file. But I was originally been making chartlets successfully on a 10" netbook laptop.  Each chart is about 500-700 Kb in size.

3. The overlay stuff on the expanded GE2KAP screen I haven't played with, but I think it allows you overlay another KAP file onto the GE screen, so, for example, you can create ONE CHART that has both the original chart (with depths) and the Google Earth view.  See Valhalla's Web Page for Instructions.

4. DON'T FORGET to turn off Terrain in Google Earth when using GE2KAP or the Geo-referencing may not be accurate on the chart produced.

5.  Naming conventions - it is helpful before you start out making charts of an area to come up with naming conventions.  I have ended up with over 100 charts of Fiji and ended up with a hodge-podge of naming.  Now when I create a new chart, I create a folder for each country and create it with the name:


Example:  VitiLevu-West-VudaPointMarina.kap

This makes it easy to use Windows' 'sort on filename' to group the related groups of chart files.  You can also put spaces in the filename--neither Maxsea nor OpenCPN cares, just keep the filename from getting too long.

You can also make subfolders by major area in a country folder, and OpenCPN (but not Maxsea) will find all the subfolders too.

Naming your chartlets Fiji1.kap, Fiji2.kap, etc is easy, but will make you (and/or people you share it with) very unhappy in the long run.

6.  When you are comfortable making charts, play with the Historical View function on the View menu (GE function only). Sometimes the current view (satellite photo) on Google Earth of a particular location is not the best for eyeball navigation.  Sometimes, you can go back in time, using Historical View, and find a photo that better depicts the location (the sun angle is better, fewer clouds, etc).

Downloading the Charts we have Already Made

At the bottom of this list of charts are links to other sets of chart sources.

If you like GE2KAP/Sat2Chart and use it, you should go online and buy Paul Higgins, the GE2KAP/Sat2Chart developer, a beer. He has spent a lot of time on this tool, and it is VERY useful to us yachties. Just think of how much money you have previously spent on charts and chart chips, and Paypal him $20

Loading Raster (KAP) Charts into Maxsea v10.3.2.1

1. File / Open (not Open Chart)
2. Browse to the directory (ie C:\Charts\GECharts)
3. Select any file (a new one you haven't previously loaded)) and click OK.

It should load ALL the charts.

To show the Raster chart window, use the menu item Window to switch back and forth between the Raster Chart and the CMap (vector) chart. All your routes and waypoints will be there! Unfortunately I haven't found a way to get the Raster and the CMap chart to track together, but you can always use the 'center on my boat' button to center up both screens so you can compare views.

So far, in Tonga, Fiji, the Marshall Islands, and Micronesia, the GE Charts have been a godsend... spot on in Niuatoputapu and Vavau, where the CMap charts are running us over land.

Loading Raster Charts (KAP and Mbtile) into OpenCPN

1.  In the OpenCPN program, click the Wrench Icon, and click the Charts Tab

2. In the upper part of the window, browse to where you have the Charts, and select one of the folders. You should see the full folder path in the box just below, something like this:

C:\Charts\GoogleEarth Charts\GoogleEarth-Fiji\

3. Click on the Add Selection button, and the folder will be added to the 'Active Chart Directories' box below. Do this for whatever charts you will plan to use in the near future.  Note that if you have chart sets stored in subdirectories, OpenCPN (unlike Maxsea) will traverse the directory tree and load up all the charts in the tree.

4. Click OK, and Open CPN will rebuild its list with your new charts included.

5. If you have 'chart quilting' turned on in OpenCPN, Play with the light blue bars at the bottom of the screen to see which level of chart you can choose.

6.  If you have C-MAP CM93 charts loaded in OpenCPN also, you switch back and forth between CM93 view and Raster chart view by clicking between the blue-colored buttons and yellow/brown colored buttons at the bottom of the screen.

See our full "Getting the Most out of OpenCPN" presentation on our Presentations Page

GoogleEarth Cache

Tip:  Use SAS.Planet and you don't have to worry about the GE cache.  It is recommended you download Paul's version of SAS.Planet, as it is pre-set-up to use with Sat2Chart.

GoogleEarth has a built-in 2GB 'cache'.  What this means is that it will save up to 2GB worth of images to your computer drive, which are accessible in GoogleEarth offline, without being attached to the internet.  When you reach ~2GB, then GoogleEarth automatically 'manages' the space for you--removing older and/or seldom-visited images to make space for new images.  2GB is actually a lot of GoogleEarth images, but you can't guarantee that an image that was accessible offline yesterday will still be accessible offline tomorrow.

I used to use a 'Google Earth Cache Management' program called "Cache for GoogleEarth" downloadable here.  It mostly works for the intended purpose (but is a little quirky).  I have had no problems restoring a saved cache if I am connected to the internet, but something in GE seems to go wrong if I try to restore a saved cache while offline.  Even with this quirk, this program saves lots of download time on slow networks if you have the time to pre-download caches on faster networks.  (ie pre-download the South Pacific Islands when in the U.S., in manageable chunks, then restore them as needed while actually cruising the South Pacific.  Now I use SAS.Planet and don't have this problem.

Converting from Maxsea PTF files to GPX Files for OpenCPN

Quick Notes:

Do the conversion in GPSU
Do NOT save the PTF file!!
Open the resulting GPX file in Wordpad or other text editor

Search and replace the following:

<sym>265</sym> to <sym>anchorage</sym> (anchor)

<sym>120</sym> to <sym>diamond</sym> (blue diamond)
or <sym>xmred</sym> (red x)
or <sym>triangle</sym> (black triangle)
or <sym>scuba</sym> (Scuba Flag)

If left untouched, the 120 will translate to a black circle.

For tracks
You need to search and replace:
<trkseg> with <trk><trkseg>
</trkseg> with </trkseg></trk>

Useful Links:

s/v Valhalla's web page on Satellite Charts and OpenCPN

s/v Ocelot's web page on making Satellite Charts