March 23, 2008

Fun with Cartographic Projections

Cartographic projections can be tough to learn and internalize, especially when GIS software does all the hard work for you. If you're an amateur photographer, you may have tried stitching together photos into panoramas. The math involved in that process happens to be identical to cartographic math. Map projections work on the outside of a theoretical sphere, and photo stitching works on the inside of that sphere. A free software package I like to use that exposes the projections that it uses is Hugin (

From Los Angeles

Eastern Columbia building, downtown Los Angeles, CA in stereographic projection. A lot of projections could have worked for stitching together these 3 images, but the stereographic projection, which preserves angles, also preserved the imposing but not overbearing feel of the building to the street. The bright stripe through the middle is due to a difference in exposure between images.

From Los Angeles

A statue of Hercules from the Getty Villa, Malibu, CA in in Transverse Mercator. In this projection one can see both the 'South pole' and the 'North pole' of the interior sphere. Seven photographs were stitched together to achieve this shot. I was running out of memory handling all seven photos at once, so I stitched the shots in two sets and then combined the two resulting photos.

From Geo Tangents

The user interface for Hugin 0.7 showing the available projections to use in this 10-photo project.