Which of the following is defined as a sharp and unambiguous natural feature used to supplement ground control in aerial photos?

The concept of a sharp and unambiguous natural feature used to supplement ground control in aerial photography aligns with the definition of a feature point. A feature point is typically a distinct and easily identifiable point in the landscape that can be consistently recognized in various images. These points are crucial in establishing accurate geospatial data as they provide a reliable means of aligning and correcting aerial photographs to ground coordinates.

In aerial surveying, utilizing feature points allows surveyors to ensure that the images are correctly oriented and scaled relative to the ground. This enhances the accuracy of topographical maps and other geospatial analyses, making feature points an essential element in the practice of photogrammetry and aerial mapping.

The other options represent different concepts: control points are specifically surveyed locations that have known geographic coordinates, picture points don’t have a standard definition in this context, and reference points could refer to various stationary markers, which may not necessarily be natural features. Therefore, focusing on well-defined and recognizable natural features clearly identifies feature points as the best category for the given definition.