Saturday, March 31, 2012

Route Planning and Sharing with gpx Files

These days we are much more likely to want to transfer data from one GPS unit to another, or to a totally different device. We may take a boat or bike trip and accumulate a neat detailed track history of the trip, showing every detour, along with speed made good at each point, and then want to show friends what it looks like on, say, Google Earth.

Or we may just have done well in a yacht race and we want to save our track and wind conditions to study next year or to pass on to others to learn the route.  Often you will see very nice lifts and headers and points or headlands or an opening into another waterway. Sometimes these wind behaviors are reproducible, so you can count on it… say, hypothetically, beating to the north you will get knocked as you approach Johnson Point, etc.

Another example is you lay out a detailed route in your PC echart program at  home and then want to transfer this to the ship’s GPS unit as well as to a couple handhelds on board as a back up.

In the old days, this was a rather tedious process, with many pitfalls in protocol along the way. Now there are several easy ways and the simplest seems to be the gpx format, called GPS exchange. Most devices and software are using this, as are as various online services.

After making your route, look for an Export option on the device, and then decide what you are exporting. It could be waypoints, routes, or tracks, or all of the above at once. Then you will choose a name and place to save the file, which will be a text (xml) file with extension, ie mywaypoints.gpx.  Sometimes you do not get to choose the name, so there is obvious virtue in practicing.

Recall, too, that routes and waypoints are well defined, that is waypoints are a list of lat-lon positions, with a name and number attached, and routes are a sequence of such waypoints. These waypoints and routes are each made from points that you personally selected, named and saved.  

Tracks on the other hand are the history of where you were — the bread crumb trail of your travels. Without getting into the nuts and bolts of the set-up and procedures of your program, you do not know how many points are saved. You could end up with many thousands of points over a longish trip with frequent records, or you may have set up the track recording to store a position every 5 minutes, or every 1 hour, or whatever.  Some units let you set tracks by distance, such as every 1 mile, or 100 yards, or 10 miles, etc. 

Some systems also compact the data for you automatically. They could for example, average every 10 data points to make just 1 after reaching some limit on data storage. In short, the saving and transferring of tracks is not so transparent, but in one form or the other you are getting a record of your actual track across the chart, but once transferred into another device you will not be able to uncompact it as you might on the original device.

Here is a sample route you can download and practice with loading into your echart program (called ECS, electronic charting system) or into Google Earth (GE). Around_Vancouver_Island.gpx. (Right click the link and choose save as. If you just click it you will see the xml format in your browser window. Also Internet Explorer may try to rename the extension xml, and if so, change it back to gpx.)

Note this sample route is not for navigation, since it is made with way outdated Canadian echarts.  We will remove this statement if we get new charts. Don’t navigate with this placemat!  In fact, don’t navigate with this under any circumstances, because every one should make their own routes choosing their own waypoints. Choosing the proper waypoints and then following them is the key to good navigation. The practice we often see of making and selling books of waypoints is a hazard and should be avoided.

With all that said, for practice, download the file to your computer, then open GE, then drag and drop onto the page. Put a check mark in all three boxes if GE asks.  Then this will be saved in your temp places on GE. 

 Here is a zoomed section


If you like you can then send these GE (klm) links to a friend to view as well. See GE instructions.

This is just a rough outline of a route.  As a rule, we make a route by roughing it out, then zooming in to fine tune the settings of each waypoint… and then giving them a name, which is always an important step. Once underway, all waypoints have to be adjusted for conditions. Night vs day, winds, and along this route the main factor is tidal current. Current can completely dominate what you do in many places. Some narrow passes here have very strong currents (ie 15 kts!).

Gpx files will transfer between PC and Mac, as well as Andorid and iOS apps, and work with any browser.

Then with a nice route laid out you can print out a Route Plan which is a hard copy to follow underway. Some ECS programs let you do this in steps, others only show the whole route, forcing you to break up the route to make pages for your Route Plan. So back to the gpx file, you may have one program you like for laying out the route, but another does a better job with the Route Plan pages. Just import the gpx route to the program you like and print the route pages from it.Below is a section of the first page of this output.

This one is from Coastal Explorer, which has a nice route plan layout function.

For a long trip, having a book or route legs (as opposed to just one large overview as shown here) is a great savings underway. That is, show the mini chart section above with the table below for a few legs at a time.  Then you can print in color and put in a note book for the trip.  Any one may have to be changed, but at least you have an organized starting point and you can paste the related tide and current data to the same pages when you know when you will be at each leg.  I will make some samples for this route when i get a chance. Generally you do it by breaking the full route into shorter sections, and printing the route plan for the sections.

To get the route into your smart phone, just email the gpx file to yourself then when it arrives you should have the option to Open with?  at which point you chose the ECS app you want to use.  With an iPhone you touch and hold the email attachment link  to get this option.

What you get will still be a surprise as the technology settles in. On an iPhone this works pretty well. MotionXGPS accepts it but interprets it as a track, but it looks good since they have charts for everywhere.  iNavX does a nice job of receiving it and storing it as real waypoints and a route,  but it will not look good unless you have Canadian charts installed.  Likewise with Memory Map—imports nicely but without Canadian charts it is not very useful on their world map. Canadian charts are available for all apps. MotionXgps has the price advantage of providing their own charts, which can be cached so if you lose connection you can still navigate by gps with your phone.
Here is a sample




4 comments:

  1. We have changed the gpx file to now include a circumnavigation finish back at Vancouver Rowing Club. See also the April 6th post which includes a gpx file of all the current stations along this route.

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  2. I don't know if Google Earth knows how to export GPX files. It can read directly from the device and lets you play with that track, but not exporting.
    You can use this simple tool http://kml2gpx.com to convert between KML and GPX files. This way you can manage the KML version in Google Earth and use GPX version to upload it to your device.

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    Replies
    1. In looking back over these earlier articles, I can add now that we have since added our own converter, which can be seen at https://www.staprath.com/gpx

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  3. HI Mike, thanks for that link and information. I will have a look at that. Seems it would be good way to set up a route... zoom in and do it on GE then export to echart program to check out the nav aids. thanks again. --david

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