As part of delineating the ordinary high-water mark (OHWM), Wenck georeferenced aerial imagery collected before the installation of the Lake Sakakawea dam. The North Dakota Department of Mineral Resources (DMR) provided single frame aerial imagery for the years 1951 and 1943. Photos were georeferenced using imagery from 2016 to match road crossings and rock outcrops. The 2016 photos were downloaded from Geospatial Data Gateway as SID files as opposed to using the streaming web service. Images were projected on the fly from NAD 83 UTM Zone 13 North to NAD 83 North Dakota North State Plane. Aerial photos included several referencing points through refinement and distorted areas were clipped on the periphery of the images.
 
Photos were inspected and clipped to remove highly distorted areas. Clipping the images on the far edge of the photos removed warping and creases; this is a legacy of scanning paper maps. Areas extending one mile outside of the draft OHWM were clipped.
 
Georeferenced photos started at the western edge of the project area and continued east to New Town. Approximately 30 to 50 control points were placed manually to reference each image. Road crossings, farmsteads, and rock outcrops were used to reference the 1951 imagery to the 2016 NAIP photos. To help with edge matching, auto-referencing was used to place high concentrations of similar points on adjacent photos. When auto-referencing was used, the amount of control points significantly increased. Auto-reference points with high residuals were deleted. A second or third order polynomial transformation was used to fit the 1951 photo to the 2016 photo. The photo was checked for distortion and warping; control points were adjusted accordingly to minimize image distortion.
 
The single frame photos were mosaiced together to create a seamless image for the project area and stored in a file geodatabase. The file geodatabase utilizes ESRI’s ArcGIS.
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