{"id":106,"date":"2007-12-29T23:13:01","date_gmt":"2007-12-30T06:13:01","guid":{"rendered":"http:\/\/www.bigroom.org\/wordpress\/?p=106"},"modified":"2007-12-29T23:13:01","modified_gmt":"2007-12-30T06:13:01","slug":"proposed-formats-for-geotagging-arbitrary-types-of-media","status":"publish","type":"post","link":"http:\/\/www.bigroom.org\/wordpress\/?p=106","title":{"rendered":"Proposed format(s) for geotagging arbitrary types of media"},"content":{"rendered":"

Yet more thoughts on geotagging – here’s what I’ve come up with so far.<\/p>\n

The format needs to handle only two fundamental data types – points and polygons. It also obviously needs to handle “lines” or tracks, but those are made of “points”. Polygon, for my purposes, might be unnecessary and I’m not sure if I should leave it in. I’m reluctant to leave it out – that way you could easily georeference media to a building or field’s outline, for example. On the other hand, I’m trying to keep this format terse and concise – I’m not trying to merely embed .gpx or .kml files in things.<\/p>\n

A “point”, as I am thinking of defining it here, is made of up to seven attributes (more or less in order of importance): a latitude\/longitude<\/span> pair, elevation, timestamp, track-ID, heading, and angle. A polygon is the same, except that it contains a list of at least three<\/span> lat\/lon\/optional-elevation sets. It still only has a single timestamp, though, just like a “point”. I suppose in some odd cases one could even define a track as a series of polygons – defining the field of view in a video taken from the bottom of an airplane that’s taking off, for example.<\/p>\n

Leaving aside the question of polygons for now, I’m envisioning two possible formats which I will arbitrarily name “geotag” (XML-type) and “geostring”(simple text) for the moment.<\/p>\n

I picture a geotag entry looking something like this:<\/p>\n

<geotag:point lat=\"41.228063\" lon=\"-115.058119\" elev=\"1720.901m\" datetime=\"20071115T143000-06\" trackid=\"1\" heading=\"340\" angle=\"-5.0\">Metropolis Hotel<\/geotag:point><\/tt><\/p>\n

In this format, the optional description of the point is between the opening and closing tags there. “lat” and “lon” might be better as a single “latlon” or “coord” attribute, with the latitude and longitude separated by commas (i.e. <geotag:point coord=\"41.228063,-115.058119\">:<\/geotag:point><\/tt>)<\/p>\n

A “geotring” point might look something like this instead:<\/p>\n

geostring:point:41.228063:-115.058119:1720.901m:20071115T143000-06:1:340:-5.0:geostring<\/tt><\/p>\n

Not sure if the closing “geostring” is really necessary here, but it would make backwards-compatibility easier if fields were added to future revisions. As with the geotag, it might be better to treat the lat\/lon pair (the only mandatory information for a minimal “point” definition) as a single field, so the minimal “geotag” example above done as a “geostring” would look something like: geostring:41.228063,-115.058119::::::geostring<\/tt><\/p>\n

Even as I write this, I find myself leaning towards combining the latitude and longitude into a single field, if for no other reason than it means each point only has one required field. Either way, I currently think the fields ought to be defined thus:<\/p>\n