How can 3D maps be made with ordinary photographs? by Adam Steer

An ordinary photograph is really a two-dimensional model of a three-dimensional world. We can also reverse the process - and figure out where an object in an ordinary photograph was positioned in the real world.

To do this we need to know a few things about the camera - we need to know how it made the two-dimensional model.

If we know about the camera and have two or more photographs that overlap, we use the camera information, image properties and matching objects in each photograph to figure out where each camera, matching object and potentially every pixel is in three-dimensional space.

So it is a big circle! A camera makes a two dimensional model out of three dimensional things. These two-dimensional models can then be combined to reconstruct a three dimensional model – which can be used for surveying tasks which are not so easy with the ‘real’ things.

Adam Steer

Every wonder how Google Maps knows where/when there is traffic? by Walter McGee

Data is collected from various sources, dependent upon: 1) how urbanized the area is and 2) the nature of the street (ie, hwy, surface road, etc.).

Real-time Traffic Sources:

-Pole mounted radar

-Surface/Ground sensors

-Video cameras

-Cell phone GPS

These are usually found in urban or on high traffic throughways and often feed a city's traffic management system. This is provided or sold to a reseller (like NavTeq) and then to Google Maps.

Cell companies can pull velocity from your phone's GPS and/or cellular tower triangulation. Nearly all streets in the US are digitized and have defined speed limits. Cell phone data is generalized, the avg. velocity is calculated, and correlated to the speed limit on that road segment. Once a threshold is met (say 60% of the speed limit) for a certain amount of time, a line changes colour and is fed to any number of online mapping systems.

Walter McGee, Operations Planning Coordinator, GeoDigital International Inc.