In recent years, with the rapid development of digital technology, photogrammetry has been applied extensively to digital images, which may be generated directly from electronic cameras or scanned from film images. The projective geometry that is the basis of photogrammetry is the same whether it is applied to analog or digital images. However, the use of images in digital form offers distinct advantages in processing and automation.
This research aims at investigating the point positioning accuracy obtainable by using monoscopic measurements on digital aerial imagery. The test imagery consists of a stereo-pair of scanned aerial images that have a 42-μm-pixel size and covers an urban area. A set of circular targets is affixed in the photographed area, mainly on roads, and measured using precise terrestrial surveying. A least-squares bundle adjustment that is based on inner constraints is adopted for the computation of unknown parameters. Prototype software is developed to implement the adjustment procedure. The achieved results have shown the feasibility of utilizing digital imagery and the consistency between the image pixel size and the attainable point positioning accuracy.