February, 2018

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Using AutoCAD's Raster Design tools, aerial imagery was geo-referenced and rectified to create a high-quality complementary basemap for vector format geographic data representing topological features such as roads, vegetation, and hydrography.

The vector data was added first, as an imported DXF block. To prepare the air photo data for processing, new layers were created to contain each of the five photos comprising the study area. The Raster Tools Import Wizard was used to add the photos, drawing relevant metadata from the image headers. Each photo was visually analyzed and several points that were easily identifiable and free of excessive vertical displacement error were chosen to be matched to their corresponding locations in the vector dataset using the Match tool. In this way, the raster data was scaled and rotated to align with the vector layers.

To reduce the effects of relief displacement and radial distortion inherent in all air photos, rubber sheeting (polynomial method) was used to rectify the images further, adding anchor and destination points between the raster and vector layers and transforming until a satisfactory result was achieved.

The five images were cropped and merged along naturally-occurring visual breaks in the imagery such as rivers or streets to create the most seamless mosaic image possible. This image and the vector features were then trimmed to a defined neatline boundary. The map was symbolized and labelled as appropriate, minor image touch-ups were performed using Adobe Photoshop, and a final print layout was created.