Vertical Photo Collage

Vertical photography is a venerable documentation technique in field archaeology. Instead of drawing plans of your site, you put clearly visible coordinate markers on the ground and photograph it from above, using a huge camera tripod or the scoop of a mechanical excavator (don't tell the health and safety people!). Then you develop the photographs and glue them together in one big collage. The beauty of this is that it's fast, accurate, hi-resolution and that you needn't have everything cleaned and ready for photography at one go. As long as you keep reasonable accuracy on your coordinate markers, you can shoot the site a few square meters at a time. But with analog chemical photography, you have to have cheap overnight photo development.

Swedish archaelogists who developed this technique were Otto Frödin in Östergötland, Björn Ambrosiani in the Lake Mälaren area and Erik Nylén on Gotland. Nylén's team produced excellent documentation in the 60s and 70s. They were technology optimists, very scientifically minded, and it's kind of sad that the glue they used back then doesn't age well. In the 90s many of their archived photo collages were falling apart and had to be restored.

Here's a vertical shot that Gustaf Trotzig took in the 60s at Barshalder, the cemetery on Gotland that I wrote my thesis about. It shows an 11th century inhumation grave. Only the lower half of the skeleton was preserved, the rest had been destroyed by looters.



Vertical photography has received a boost in recent years thanks to the adoption of digital cameras and image processing software. These days, you need no photo lab and you can start removing stones seconds after shooting the site. Also, you no longer need to take exactly vertical photographs. If you make sure there are four coordinate markers in each shot, the computer can rectify them for you. If they're really good, the machine can even do the stitching for you.

As often mentioned here, my friend Howard Williams and myself dug a 9th century boat grave last summer. We saved enormous amounts of time by not planning the site by hand. Instead, intrepid Howard scaled the land owner's aluminium ladder and took oblique digital photographs of everything. Each shot covers a bit more than four square meters. They have been sitting on my hard disk ever since, and in the last couple of weeks I've processed them and put them together using AirPhoto and PhotoShop. Here's what came out. The coordinate crosses are one meter apart. Any PhotoShop wizards around who can help me get the colour more uniform?



I'm really thrilled to be using the methods of my scholarly fathers with modern equipment. The question now is, how do we get an archive longevity comparable to that of monochrome photographs? I should probably try to find a lab willing to print the collage on the same Ilford stuff that they used in the 60s.

[More blog entries about photography, excavations, documentation, archaeology, Sweden; foto, fotografi, dokumentation, utgrävning, arkeologi, Östergötland.]