hebig.org/blog

Similar to digital photos that are time tagged, geotagging is to (automagically) add geographical metadata like latitude and longitude to content items. Geotagging photos of public lettering could be a good example. Public Lettering can appear in an infinite number of places while the exact location is an essential part of the photo's context.

My digital camera records timestamps in the EXIF data, so a second device should record geographic coordinates over time and timestamp these, and software would glue those two datasets together. The obvious solution is to use a handheld GPS receive. Current models are small, leightweight, cheap and powerful; some even output recorded tracks and waypoints in XML format. As I don't have a GPS receiver, enter solution 2: To use a GSM cell phone.

My provider O2 Germany has all its cells transmit their geographical coordinates and segment ID (?) as cellbroadcasting messages. (This is for their "Homezone" feature that gives you lower rates in a nearly circular area around a location you specifiy, eg. your house). So if you log all incoming CB messages on a computer, you get a timestamped list of the coordinates of all cells used (actually, one could even log the coordinates of the main cells and of up to six neighbouring cells). When adding data available on the net, like cell surface or antenna directions, the resulting waypoint list could be a "good enough" solution. Accuracy would be higher in urban areas with a higher cell density (read: less surface served per cell) and would decrease significantly in rural areas where single cells can serve several square kilometers. More on that later after I will have recorded some sample data sets.