sat, 29-nov-2008, 10:20

GPS track

GPS track, Goldstream Creek

I just got back from walking Nika and Piper on the Creek. I’d looked at my GPS track from yesterday’s walk on the Creek and saw an obvious shortcut (from point A to B on the map) to cut off some distance. My objective was to take the Creek out to a section line (at points D and E—click on the image to see a full size version) that I also saw from the satellite imagery for the area, and wanted a way to make the route shorter. Yesterday’s walk was more than five miles, even though a raven could have covered the distance in a little over a half mile.

We walked down the Creek, came to the start of the shortcut at point A, walked overland through the forest to point B back on the Creek, and I immediately turned the wrong direction. I’d already walked about halfway back to point A before I realized I went the wrong way. Next time, turn left!

It is amazing how disorienting the Creek is, even with a GPS. Because it winds back and forth so much, even if you know where you’re going and can see it on the little map your GPS is showing you, it’s really difficult to tell if you are getting closer to your objective. The good thing is that the Creek only goes two ways. If you went the wrong way, just turn around and go back.

tags: GIS  Goldstream Creek  GPS  Nika  Piper 
sat, 10-nov-2007, 14:55

Bridge and house from the creek

bridge and house from the creek

I took Nika out on the Creek today to see how far we could get on the ice. All of the open water on our property had frozen more than a week ago and we’d noticed bicycle tracks and footprints in the snow, so I figured it was probably safe to walk on. Plus I wanted to see where the bicyclist was coming from. The photo on the right shows our bridge and the house from down on the Creek, and the photo at the bottom of the post is a Google Earth view of the GPS track we walked. The red dot is our house, and the blue dot is where we got off the Creek.

I would have kept going on the frozen Creek, but there was a small dam at that point and I could hear running water just below the surface. Just past the dam was a hole in the ice with water running underneath and I didn’t want to take a chance of falling in or having Nika break through the ice. It turns out that were we went back up onto land is a section of trail between two roads that were originally supposed to intersect. At least that’s how it looks on the map.

The bicyclist is using this trail, the Creek, and our road to travel between the two roads that don’t intersect, which is pretty clever and is probably several miles shorter than where they’d have to go to get around the break.

Garmin hasn’t come up with the software for my GPS for Linux or OS X, but gpsbabel lets me download the data from the GPS and will also convert it into a KML file I can view in Google Earth. It works really well, except that in our area Google Earth isn’t perfectly geolocated, so the GPS track isn’t lined up with the satellite topography shown. The commands are:

$ gpsbabel -t -w -i garmin -f usb: \
    -o garmin_txt,date="YYYY-MM-DD",datum="WGS84",dist=s,prec=6,time="HH:mm:ss" \
    -F out.txt
$ gpsbabel -t -w \
    -i garmin_txt,date="YYYY-MM-DD",datum="WGS84",dist=s,prec=6,time="HH:mm:ss" \
    -f out.txt -o kml -F out.kml

You could take the GPS data directly to KML format but it’s handy to have the text version first so it can be edited before generating the KML file. The -w flag to gpsbabel causes it to download all the waypoints from the GPS, and I usually want just the waypoints relevant to the current track (the -t flag). The text file makes it easy to remove the waypoints you don’t need.

Creek walk, Google Earth view

google earth view

tags: creek  Google Earth  GPS  gpsbabel  house  KML  Nika  trails 

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