Then and now

A couple of weeks ago I posted on the Flickr pool "Looking into the Past". I'm getting a chance to do some similar work now:


One of our librarians wanted to create a poster of an "architectural history" of medicine at the University of Michigan, displaying photos of major medical buildings. I'm taking that a step further: creating photos that juxtapose the past with the present, and a KMZ file that can be displayed in Google Earth to locate each building's footprint on a current map.

I start with a Sanborn map fitted to the street grid and any still-existing landmarks. Then I plot the shape of the buildings according to the map, like so:


After that, it gets complicated. I can measure the true dimensions of a building and compare that to the apparent dimensions of the same building in a photograph to calculate the angle at which the photographer was viewing it. Or, as in the photo at top, I might be able to see the corner of one building lines up with a certain section of another building or landmark. If I have more than one line, I should be able to triangulate a nearly exact location for the camera:


Of course, it's not really exact, due to errors in my calculations, my alignment of the Sanborn map, and small inaccuracies in the Sanborns themselves. But it's surprisingly close and saves a lot of time when I go to reshoot the scene. When you're trying to match up two photographs, it only takes a small difference in vantage point - like ten feet - to spoil the effect, so if I had to do it all by guestimating, it would take an enormous amount of trial and error before I found the correct spot.

Even then, the trouble isn't over. The new photo and the historic photo have different dimensions, so one of them will have to be resized. How much? It can be tough to tell. In the example above, I originally had the old buildings much too large and only realized it by comparing the sizes of the two figures on the sidewalk. After I made the adjustment, I went back to Google Earth and drew some new lines, confirming that yes, most of the third building would have been visible around Angelo's restaurant.

Here is what the scene looks like today, with the Taubman Medical Library partially obscured by Angelo's:


The historic photo, showing the University Hospital in 1915, can be seen here at the Bentley Historical Library site.