Supposedly, we’re due a long hot summer here in the UK. Call me cynical, but I’m not entirely sure I believe this. The weather just lately has been mad – bright sunshine one minute, dull and cloudy the next. Yesterday, the wind got so strong at one point I was struggling to walk into it. An hour later, it was glorious sunshine again.

Today looks to be a washout, with little chance to get out exploring (although as I type this, the sun has suddenly decided to show itself again!) so I decided to set about trying to convert the Defence of Britain Database to Garmin format so I could upload it to my Nuvi satnav.

In practice, this didn’t turn out to be too difficult a task, but there are a couple of points that are useful to know so I thought I’d share them in case anyone else has difficulty doing the same thing. Before attempting the process, ensure that you’ve got 50mb of free storage on your Garmin device. If not, you may have to clear some existing data from the unit before you can begin.

Firstly, you’ll need to download the DoB Google Earth database from the Council for British Archaeology’s website. The download can be found on this page.

Secondly, you’ll need a copy of WinRAR (or a similar zip file utility for your host operating system). A 40 day trial version can be downloaded from their website.

Most people will probably have a copy of Garmin’s POILoader already installed. If you don’t, you can download it for free from their website.

Finally, you’ll need a copy of GPSBabel, which is a free open source download. Download this and extract it to a folder on your hard drive.

Once you’ve got all of the above installed, launch WinRAR and browse to the Google Earth Defence of Britain Google Earth .kmz file. Double click the file and WinRAR will decompress it into .kml format. Highlight the .kml file, click on “Extract to”, save the .kml file to your hard drive, then close WinRAR.

Next, browse to the folder where you extracted the GPSBabel files, then double-click GPSBabelGUI.exe to launch the convertor.

Within GPSBabel, click the drop down list for the input file and select “Google Earth (Keyhole) Markup Language (.kml)”. Click the input file dialog button, then select the .kml file location for the unzipped file which you extracted using WinRAR.

Next, select the drop down list for the output file and select “GPX XML (.gpx)”. Click the save file dialog button and pick a location to save the prepared file ready for upload to your Garmin device. The button marked “Let’s Go” should now be ungreyed in GPSBabel’s user interface. If so, click the button and the file conversion will start. The command line parameters being used will then display in the lower pane and not much else will appear to happen for a period of time. Depending on the speed of your system, this may take a while, but wait and a pop-up dialog will appear confirming the file has been converted successfully. Once this happens, close GPSBabel.

The file is now ready to upload, so connect the Garmin nav unit to your computer using the Garmin USB data lead and launch POILoader.

Follow the command prompts within POILoader, selecting “Garmin Device” as the output location then connecting to your device when prompted. POILoader will then ask whether you want to replace or update your existing points of interest. You’ll probably just want to install the new POIs unless you’ve got a lot of data you don’t need on the unit at the moment.

POIloader will then ask for the file location. Browse your hard drive and select the folder where you saved the output file from GPSBabel. Select your preferred measurement unit, then ensure that the import mode is set to “Express”. Click on next and the upload to your device will now begin.

The full Defence of Britain database is getting on for 50mb in uncompressed gpx format, so uploading will take a fair amount of time. During the process POILoader may appear to be locked up and Windows may report it as “Not responding”. Ignore this and leave the upload to progress. DO NOT unplug the data lead or attempt to kill the upload process within Windows. It may take 5-10 minutes for the upload to complete, but you’ll eventually find that POILoader can be selected again and will report that the file has been uploaded successfully. In my case, I got a dialog advising that 15449 POIs had been added.

Disconnect the data lead, wait for the Garmin unit to restart and you can now select the Defence of Britain locations within the Garmin menu. If you’re out and about and want to know what’s in the local area, fire up your Garmin, select “Where To?”, then “Extras” then “Custom POIs”.  The unit will then produce a list of local sites which you can select and navigate to or view on the map.

One minor issue with this method is that extra HTML formatting is left in place, which looks a bit unsightly on the site summary. This doesn’t really bother me, as you can simply select “More” and get a nicely formatted page with full details of the site. There doesn’t appear to be any easy way to remove it during the above process, so I may code something to strip the HTML from the summary field in the XML at some point but, then again, I may just live with it and spend the time exploring instead 🙂

All of the above works for my Garmin Nuvi 200w, so should work with similar or newer units.

Local POI list

Local POI list

Area Map with POI display

Area Map with POI display

Site Detail

Site Detail


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