FIGURE 2.4 Recovery of three-dimensional target points requires at least two overlapping images, which is the basis for accurate stereo photogrammetry.

BOX 2.2
Photogrammetry and Remote Sensing

Both photogrammetry and remote sensing originated in aerial photography. Before it was called remote sensing, this field focused on identifying what is recorded in a photograph. By contrast, photogrammetry was concerned with where the recorded objects are in geographic space. Therefore, photogrammetry required more information about the photography, such as the camera characteristics (e.g., focal length, lens distortion) and aircraft trajectory (e.g., altitude, camera attitude Airphoto interpretation requires less precise knowledge of the geometry of the photographs; it may suffice to know the approximate scale.

The term remote sensing was introduced with the advent of systems that sense in several regions of the electromagnetic spectrum. For decactes, remote sensing involved many of the same activities as photogrammetry at a coarser resolution, but contemporary remote sensing can image at resolutions equivalent to those used in photogrammetry. What used to be almost entirely done by a human—the interpretation of photographs—has now been replaced by sophisticated algorithms based on mathematical pattern recognition and machine leaming. Nevertheless, the fundamental tasts of the disciplines remain essentially the same. In photogrammetry, one deals with the rigorous mathematical modeling of the relationship between the sensed object and its representation by the sensor. Through such models, various types of information can be extracted from the imagery, such as precise positions, relative locations, dimensions, sizes, shapes, and all types of features. High accuracy is critical. For example, accurate modeling is used in multiband registration of multispectral imagery. In remote sensing, the goal is usually to transform an image so that it is suitable for mapping some property of the Earth surface synoptically, such as soil moisture or land cover.

primarily in batch mode. The transition from analog to analytical was epitomized by the introduction of the analytical plotter in 1961, which incorporated a dedicated computer. The development of the digital photogrammetric workstation ushered in the stage of digital photogrammetry.

Advances in optics, electronics, imaging, video, and computers during the past three decades have led to significant changes in photogrammetry. Film is being replaced by digital imagery, including imagery from active sensors, such as radar and, more recently, lidar.3

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