Mapping The Battle of Gettysburg

GeoCue Group recently partnered with the National Park Service (NPS) in a pilot project to assess culturally significant areas within Gettysburg National Military Park using small unmanned aerial systems (sUAS). The area of interest (AOI) for this project was the western face of Little Round Top. Little Round Top was the location of a defensive stand by the Union army during the Civil War Battle of Gettysburg. On July 2, 1863, Confederate forces attempted to capture Little Round Top—the left flank of the Union line (Pfanz 1987). This fight included the famous bayonet charge led by the Union Army’s 20th of Maine Volunteer Infantry Regiment, under the command of lieutenant colonel Joshua Chamberlain, who captured and repelled the advancing Confederate Army’s 15th of Alabama (Desjardin 1995). The Confederate attack was ultimately unsuccessful. The Union Army would use the hill to counterattack and as an artillery battery position later in the Battle (Hall 2003).

Figure 2 – NPS map of prescribed burn area

The equipment and software used for data collection and processing are detailed below.
• Global Navigation Satellite System (GNSS) Real Time Kinematic (RTK) base station and rover
• SenseFly eBee RTK
• DJI Inspire 2
• Ground Control Point (GCP) targets fabricated by GeoCue
• Mission Planning – Emotion 3 and DJI Ground Station Pro
• Data Processing – PhotoScan (Point cloud, orthomosaic generation)

Twenty-nine checkpoints were placed and measured inside the AOI to verify the accuracy of the drone collected data. These checkpoints are 1-foot square tiles with a 4-block, black and white checkerboard pattern. The locations of these points were collected using the GNSS rover.

By bringing the orthomosaic into LP360, the planimetric accuracy of previously derived features was identified. Coupled with the detailed orthomosaic, the point cloud introduced many new objects undetected in previous surveys. Using the classification and feature edit tools in LP360, various park resources such as earthworks, stone walls, and railroad beds can be extracted increasing efficiency in the cataloguing process.

Using sUAS systems proved to be an effective solution for an accurate aerial survey of the culturally significant area of Little Round Top. This system could be used in the future to map small strategic areas in other National Park System areas. A special thanks to Curt Musselman, Gettysburg National Military Park Cartographer, for his assistance on this project.

Pfanz, Harry W. Gettysburg – The Second Day. Chapel Hill: University of North Carolina Press, 1987. ISBN 0-8078-1749-X.
Desjardin, Thomas A. Stand Firm Ye Boys from Maine: The 20th Maine and the Gettysburg Campaign. Gettysburg, PA: Thomas Publications, 1995. ISBN 1-57747-034-6.
Hall, Jeffrey C. The Stand of the U.S. Army at Gettysburg. Bloomington: Indiana University Press, 2003. ISBN 0-253-34258-9.

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