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Old 21-02-2010, 07:42   #1
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Using Google Earth as a Navigation Program

This may have been mentioned within other threads but I would like to share how you can use Google earth as a navigation program.

As we all know you can look at your proposed routes on GE online. Then when you're offline, the cache in GE will display the route again and follow it by connecting a GPS to GE.

But what you may not know is you can save the cache files and restore them later when needed. Thus you can build a library of cache files with your routes. The GE cache files consist of two files, the datbase and the index. You have to save both files :
dbCache.dat
dbCache.dat.index

They can usually be found:
in Vista:
C:\Users\userid\AppData\LocalLow\Google\GoogleEart h
in XP:
C:\Documents and Settings\userid\Local Settings\Application Data\Google\GoogleEarth

If they are not there you can use regedit to find: cachepath. Not sure where they are on linux.

Before you start saving the cache you should delete both files (with GE not running) then start GE. The caches can be up to 2Gigs in size which is pretty big. I did from Mexico to Panama and it took 1.7Gig. You should make sure its set to its maximum by going into Tools..Options.Cache.

You can build your routes by either scanning along while GE is online, or you can create a path and let GE follow the path as Tour. Set the camera height and speed in Tools..Options..Touring. Be sure the speed is slow enough to allow the GE server to download the data, this will depend on how fast an internet connect you have. I set the camera height at 3000 (975 meters) feet and the speed at 89.5 (slow). Whenever I need more detail and zoom into a 1000 feet.

I wrote my own program to convert all my SeaClear routes or tracks to GE .KML files so it was easy to follow them with a GE tour.

BTW I followed my tracks from Toronto Canada to Mexico and GE was never off (went over land) except when it was also off on the charts. Which means there must have been a problem with the GPS signal (this usually happened near power lines). So I have no doubt about the accurracy of GE.

Of course it doesn't give you depths but often you can see the shallow water. Also, you can use waypoints from other cruisers or cruising guides to create your routes.
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Old 21-02-2010, 08:10   #2
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And as a passage planning tool

I've been using it recently to do some passage planning. It's great for that as you can create routes and quickly and easily determine distances between locations. You can also get ideas for places to visit. Google Earth, Wikipedia, Noonsite, Weatherbase (for temperature averages), and Cornell's World Cruising Routes is what I'm using with seemingly good results.
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Old 25-02-2010, 01:00   #3
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Paul,

This might not be news to anyone, since I am new to using GE. I use it with Bungee, a shareware program that costs very little and allows you much control over GE. It's pretty slick and a lot of cruisers in this part of the world use the GE/Bungee combination to supplement charts, whether raster or vector, which tend not to be very accurate.

GE seems to be much more accurate. Some cruisers contend they can tell shallow depths within a metre or two depending on the shade. I will trust it and myself only to a point, though I have found dark water is just that, and deep enough for my draft. I haven't tried to load tracks yet (having too much fun getting to know openCPN and have converted most of my library of tracks to the GPX format it uses), but will.

As was explained to me, I located dbCache.dat and dbCache.dat.index. Then saved them both in a new folder so I had them stored and they wouldn't be automatically deleted when I oversaved them. Not sure the purpose of this, but I did as I was told. I think we arrive at the same end.

I have found that when I save a file in the position where I am, the high-res pictures will be good for about 100 miles around, when I will have to reconnect to the internet and again save my position.

But I would find it much more useful if I didn't have to periodically connect to the internet, and have thought that it would be nice if GE allowed you to download DVD-sized files of certain parts of the world so that you could access them at will.

Sorry if this has been discussed before, but your post caught my attention. I am curious how you go about saving routes to cache. Before you set out, do you follow your proposed route, saving images along it to cache, and find that you have high-res GE images along that route? How far apart do you find you have to save images? This might certainly solve most of my perceived shortcomings of GE. Perhaps I could save a couple gigs of images, store them on a flash stick, then save a couple gigs more, etc.

Also, my disk cache size is set the maximum 2000mb. My memory cache size is set to 192mb. Do you know if the size of the memory cache plays a role in determining how big an area is cached each time you save an image?

Any thoughts on this?

cheers, Jim
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Old 25-02-2010, 03:02   #4
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I also enjoy GE for passage planning purposes, thanks for the caching hint.

The excellent Capcode has a built-in NASA world wind plugin, I believe the datasets for world wind can be downloaded on a per-region basis.
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Old 25-02-2010, 03:10   #5
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why dont you just buy charts?
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Old 25-02-2010, 03:14   #6
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We do buy and own charts, we are talking about additional orientation info here.

Btw I find the topography on GE particularly helpful for finding valuable geographical points of reference on land.
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Old 25-02-2010, 03:23   #7
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Fair enough. I'm just old school and a little grumpy this evening. Cheers.
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Old 25-02-2010, 04:49   #8
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you think YOURE grumpy. Google Earth's images of our area are from 2004. There have been huge changes in six years here. Canals dug. New marinas. Lots of new landmarks in the forms of hotels, etc. Sand bars have shifted.. Google Earth is way behind.
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Old 25-02-2010, 06:07   #9
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Navionics for iPhone ($9.99 - $19.99) will let you build a route and send it via email. It attaches 2 files to the email, one for Navionics and one for GE. It works great - build the route using Navionics and review on GE.
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Old 25-02-2010, 06:18   #10
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Jimbim,

Here are the steps I follow to cache a route:

1. With GE not running delete the two cache files in the location I stated.

2. Start GE it will recreate the cache and start adding to it.

3. Zoom in to the area you want, close enough to give you the detail you want. I usually go for 3000' but when I get to something like a reef or harbour I go into 1000'. Along coastlines where you know you'll never stop, 10,000' is OK.

4. After you completly follow the route, stop GE.

5. Copy the two cache files someplace. I have a USB stick with a folder called GoogleEarth_Caches. I create subfolders for my routes like NewYork_to_CapeMay. Each of the subfolders will have the two cache files for a particular route.

6. When I'm offline and want to look at a particular route, I stop GE and then copy the two files from my USB stick subfolder into where GE expects to find its cache files in the location I stated(in Vista:
C:\Users\userid\AppData\LocalLow\Google\GoogleEart h\).

7. Then I restart GE and zoom into the route. GE retrieves the data from its cache but it will only give as much detail as you have put in there.

I don't think the size of the memory cache has much affect. Just have the disk cache set to its maximum and make sure you never go over the 2 Gig when creating a route as you would then be overlaying the start of the route.
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Old 25-02-2010, 06:36   #11
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Quote:
Originally Posted by phiggins View Post
I wrote my own program to convert all my SeaClear routes or tracks to GE .KML files so it was easy to follow them with a GE tour.
Hi Phiggins,

Would you be willing to pass that program on to the rest of the group? I use SeaClear II and have been looking for something like this.

Tim
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Old 25-02-2010, 08:51   #12
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Tim,

I'd be glad to share it but first let me tell you that there are few steps involved.

First my program is written in a language called REXX so you have to install the Rexx interpreter which is very easy.

Second I can't actually read SeaClear routes and tracks directly as I don't know the format of them. So you first have to create the route, then store it as text file (Seaclear provides an option to do this) then my program reads the txt file and converts it to either/both a .GPX or .KML file which Google Earth can read.

If you want the program, then PM me and give me your email address and I'll send you the program and instructions to install and run it.
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Old 25-02-2010, 09:36   #13
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I use a free download called GEVoyager (Google it) to fill my GE cache. It lets you define an area, resolution (Altitude). With a little practice you get a feel for how much fits in the 2 Gig space.

Dave
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Old 25-02-2010, 09:54   #14
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GE and depth

Of course it doesn't give you depths but often you can see the shallow water. Also, you can use waypoints from other cruisers or cruising guides to create your routes.[/QUOTE]
There is this web site that has GE and nautical charts as an overlay for depth. Maybe you can incorporate this feature in your set-up.

NOAA



Tom
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Old 25-02-2010, 14:41   #15
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Thanks for all the suggestions. I'll have to look into them to see if it makes the caching and depths easier.

If you want a real challenge, try caching Chesapeake bay, especially the east side.

Regarding the questions of why not just buy charts, in most cases the coastline hasn't changed much. Also in some cases Google Earth is much more uptodate and more accurate. Take for instance some of the Mexican charts like for Puerto Morelos 28201. This chart is from a survey in 1905. It differs from GE by nearly 2 nautical miles in longitude. The different datums used, can't account for that much error.
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