Sunday, February 17, 2013

iPhone and iPad Navigation

I've spent some time at various anchorages this year looking into Navigation using iPhones and iPads.

Many people use INavX. INavX is a commercial app that is from the same folks that provide GPSNavX, which is a good Mac based navigation program. The difference is that while GPSNavX allows the use of all BSB charts, which are widely available and mostly free, INavX requires purchased charts. There is nothing wrong with purchased charts as long as they are accurate, but the fact is that in quite a few cruising grounds, scanned charts from good cruising guides that are then calibrated are much more accurate and much safer than commercial charts. The San Blas Islands in Panama are a prime example. We often crossed over the shallowest part of reefs and anchored on islands according to our Raymarine chart plotter with Navionics, but while using GPSNavX on a Macbook with scanned Bauhaus charts the Mac screen duplicated reality as seen from the cockpit.

Problem solved… sort of. On Passport, I have installed an Aircable Mini, a bluetooth transmitter connected to the NMEA data stream from the chart plotter. This allows our computers to receive position information wirelessly. That eliminates one cable, but we still have a power cord to the cockpit, the inverter on, and since a computer has not been our main chart plotter, we have no provisions to keep the Macbook dry if it rains.

Wouldn't it be nice to have this ability on an IPhone or IPad? Should be easy, but in reality it is a bit complicated. Back to the problem stated above. Although there are several navigation apps for Idevices they mostly require purchased charts which are not accurate in our current locale.

Enter Memory Map.

Memory Map is a windows based navigation package that has been around for a while. They now also provide a version of the program as an app for IPhone and iPad. The app is free but once again you must buy commercial charts. But for $50 you can unlock the app to use 3rd party charts or scan and calibrate your own images into charts. They will provide a 30 day free trial of this feature. So for $50 you have a method of using iPhone or IPad for navigation with good 3rd party charts. Now the downside. Memory Map uses a .QCT file type which is their own proprietary file type which is difficult to convert to. However with the $50 unlock, you can import .BSB charts, although they sometimes require additional recalibration, or you can import scanned images and calibrate them yourselves. There are .QCT charts for the San Blas and some other areas that are traded around the southern Caribbean by cruisers, which will save the work of scanning and calibrating. They were given to me for the (ahem) Windows version of Memory Map but work fine in the Idevice Apps. One killer caveat: the import and calibration of new charts must be done in the Windows program and is not available in the apps. You do get license to run the Windows version and calibrate charts included in the $50 app unlock fee. Memory Map is not available as a MacOSX program so to put it through all its tricks you must have a PC or a Macbook with dual boot or Fusion, etc. to run Windows.

Google Earth

Another interesting option for navigation with an Idevice is Google Earth. I have only used Google Earth to enter a very few anchorages so far but in my limited experience it is amazingly accurate and very clearly shows the shallow water. Of course there are no navigation aids, depth soundings, or anything else that you have on a proper chart, but you end up with a powerful and useful backup to charts and visual navigation. To get the images you need for navigation you first need a data connection for internet. I start off by clearing the cache, done from the settings menu in Google Earth. Then zoom in on each anchorage or tricky passage area you will need to see while underway. Once this is done, turn off the cellular data on the device you are using. The areas you zoomed will remain in the Google Earth cache and allow you to see those zooms again while you are underway. This does require that location services are on and that the device you are using has a real GPS. Some older iPhones did not have GPS, they get location by interpolating from towers. This is NOT suitable for  navigation. If you are using Google Earth on a computer you must have an external GPS connected to the computer. Also, beware that as you continue to use Google Earth with the internet on the cache will eventually erase the oldest stuff and you will lose your navigation zooms.


Unless you save your cache. There are very good instructions for doing this on computers on the web so I'm not going to reproduce that here. What I haven't seen on the web is any information for how to do this on an iDevice. Here is how you do it. Download Iexplorer from  Version 2 used to be free. They are up to Version 3 now and want money because they added some new features. But none of those features are needed for what we need to do with Google Earth. Just run Version 3 in the demo mode. It doesn't expire.

When you hook up your Iphone or iPad to the computer running Iexplorer you will see the file structure of the device. The Google Earth cache files live in a folder:

apps/google earth/library/caches/cache/

Save the 'cache' directory in a named directory on your computer hard drive. Copy them back to the iDevice as needed and you will have the navigation zooms back. Be very careful to put things back exactly as they were. For example I created a directory called Google Earth Zooms on the computer hard drive. Under that I created a directory call Honduras Bay Islands. Drag the 'cache' directory from the Iexplore window onto it. To put it back drag the 'cache' directory onto the 'caches' directory above. This is standard stuff but you want to be fluent in moving stuff around between directories. Many people are not. Be warned!

Even Better...

There is retired systems analyst that has taken all this Google Earth navigation to the next level. He has developed a free package that will convert Google Earth zooms into actual .BSB navigation charts. There is even a plug in that allows it all to be done in OpenCPN. Download links are at It is even possible to overlay Google Earth zooms with charts and create combination charts.  The charts created work perfectly with GPSNavX and OpenCPN. It is a bit difficult getting them into Memory Map for iDevices. I have worked out a way to do it, but for my purposes just having the Google Earth zooms is painless and serves our purposes. Email me for more info if needed.

Pocket Earth

The final piece to the iDevice navigation scene for Passport is an app called PocketEarth Nav by Geomagik. Not to be confused with Pocket Earth by someone else that shows views of the earth from the sun or something. Pocket Earth uses Open Street Maps and provides worldwide free road maps. Open Street Maps is a map wicki which will improve as millions of nerds update the maps. I count myself among them. This summer I updated my neighborhood's roads, bike and hiking trails on OSM which now show up on Pocket Earth and any other app using OSM data. We have found it very useful navigating the towns and islands in the Caribbean. Most roads are already there and they are often better than in the expensive apps sold for individual countries. You need data service to get maps but once loaded the maps are available offline. The app does routing but is tricky and you have to be online to get a route which is then saved for offline. Routing is perhaps mostly useless compared to a good automotive GPS but at $1.99 we have found Pocket Earth to be very useful for finding our way around almost anywhere. For cruisers interested, it is pretty easy to take a track from a handheld GPS  and add hiking trails, roads not currently on the maps, and points of interest to Open Street Maps. Once entered they will show up on Pocket Earth within a week or two. Go to for more information on free membership and editing. There is also a topo map based version for hikers and cyclists.

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