Location Verification: Siting Tyson’s 1863 Photograph of Camp Letterman General Hospital

Abstract

Gettysburg Magazine, no. 52 additional calculations to arrive at a solution. It is accomplished by choosing four points and matching the absolute value of the diff erence in the calculated focal length for each pair of points. Since all the reference points are from the same print, the focal lengths, though unknown, must be the same. Instead of producing two candidate points for the resulting camera position, the technique produces two continuous lines for which the diff erence in calculated focal lengths in near zero. Th e intersection of the two lines represents the candidate camera position. In order to validate the technique, I chose two observation locations close to the 1863 camera position specifi ed by Frassanito northeast of the town center. Th e fi rst position was on the fourth fl oor of the Hilton hotel just east of York Road. Th e second position was at a high point near the intersection of Natural Springs Road and Camp Letterman Drive. I used my Canon eos Rebel electronic camera and a 100– 300 mm lens to take pictures of the set of buildings visible in the background of the Tyson print. Details of the modern photos contain much of the same area contained in the background of the Tyson print. I selected and marked nine identifi able Gettysburg locations. Photoshop was used to mark and measure the distances between pairs of locations. Th e nine locations, left to right, are the southeast corner of the German Reformed Church, the northeast corner of the German Reformed Church, the northwest corner of the German Reformed Church, the southeast corner of the public school, the elevator shaft of the public school, the Gettysburg Presbyterian Church steeple, the United Using spatial methods and buildings visible in the background of the 1863 Tyson Letterman Hospital cartedevisité (cdv), this article describes an attempt to verify the location of the scene as identifi ed by William A. Frassanito by comparison to modern photographs and new technological approaches. Th e Tyson Brothers exposed a series of plates and a cdv in September 1863.1 In the background of the cdv a portion of the city of Gettysburg is visible. Visible in the background are several buildings (the German Reformed Church, a public school, the county courthouse, etc.) that remain in Gettysburg to this day. In Early Photography at Gettysburg Frassanito determined the camera location by studying the buildings relative to the distant mountains and the 1863 Bachelder and 1874 Warren maps.2 At the suggestion of Curt Musselman, National Park Service Cartographer at Gettysburg National Military Park, I looked for a second and hopefully more precise technique for verifying the camera position. Aft er some study, I employed a technique based upon measuring the relative distance between two points on the cdv print and gis (geographic information system) tools to match the measured distance against the actual distance between the same two points on the ground. Had the focal length of the lens used by Tyson been known, the technique would result in two solutions for the camera location— one in front of the points selected and one behind them. Since I was unable to fi nd a reference to the focal length, it was necessary to perform