This link has been bookmarked by 13 people . It was first bookmarked on 31 Oct 2008, by Steve Ersinghaus.
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Alan LevineWe have a lot of geotagged photos
Almost ninety million, as I write this, and the numbers keep growing especially as nearly every new "smart" phone released to market has not only a camera but also the ability to capture location information with it.
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Carlos SantosFlickr is creating map shapefiles from geotagged images; they open-sourced the software they use.
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Shawn MillerOver time this got us wondering: If we plotted all the geotagged photos associated with a particular WOE ID, would we have enough data to generate a mostly accurate contour of that place? Not a perfect representation, perhaps, but something more fine-grai
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raman srinivasanlmost ninety million, as I write this, and the numbers keep growing especially as nearly every new smart phone released to market has not only a camera but also the ability to capture location information with it.
For every geotagged photo we store up to six Where On Earth (WOE) IDs. These are unique numeric identifiers that correspond to the hierarchy of places where a photo was taken: the neighbourhood, the town, the county, and so on up to the continent. This process is usually referred to as reverse-geocoding.
Over time this got us wondering: If we plotted all the geotagged photos associated with a particular WOE ID, would we have enough data to generate a mostly accurate contour of that place? Not a perfect representation, perhaps, but something more fine-grained than a bounding box. It turns out we can.
So, starting today there are 150,000 (and counting) WOE IDs with proper (-ish) shape data, available via the Flickr API. What kind of shapes, you ask?-
o GIS information was harmed in the creation of these shapes.
How cool is that?!
How does it work?
The short version is: Scary and complicated maths. The longer version is: We are generating alpha shapes using the set of unique latitudes and longitudes associated with a WOE ID. The long version, to quote Tran Kai Frank Da and Mariette Yvinec, is:
“Imagine a huge mass of ice-cream making up the space … and containing the points as
hard
chocolate pieces. Using one of those sphere-formed ice-cream spoons we carve out all parts of the ice-cream block we can reach without bumping into chocolate pieces, thereby even carving out holes in the inside (eg. parts not reachable by simply moving the spoon from the outside). We will eventually end up with a (not necessarily convex) object bounded by caps, arcs and points. If we now straighten allround
faces to triangles and line segments, we have an intuitive description of what is called the alpha shape…”(There are also some useful illustrations of what that all means on Francois Belair’s Everything You Always Wanted to Know About Alpha Shapes But Were Afraid to Ask website.)
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lmost ninety million, as I write this, and the numbers keep growing especially as nearly every new
smart
phone released to market has not only a camera but also the ability to capture location information with it.For every geotagged photo we store up to six Where On Earth (WOE) IDs. These are unique numeric identifiers that correspond to the hierarchy of places where a photo was taken: the neighbourhood, the town, the county, and so on up to the continent. This process is usually referred to as reverse-geocoding.
Over time this got us wondering: If we plotted all the geotagged photos associated with a particular WOE ID, would we have enough data to generate a mostly accurate contour of that place? Not a perfect representation, perhaps, but something more fine-grained than a bounding box. It turns out we can.
So, starting today there are 150,000 (and counting) WOE IDs with proper (-ish) shape data, available via the Flickr API. What kind of shapes, you ask?
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