Though aerial photogrammetry is rather expensive and slow in air flight as well as subsequent photogrametric plotting and editing, it is still very important to input accurate and up-to-date spatial information. Aerial photogrammetry needs a series of the procedures including aerial photography, stereo-plotting, editing and output as shown in Figure 3.5.

There are two types of aerial photogrammetry.

a. Analytical photogrammetry
Though computer systems are used for aerial triangulation, measuring map data, editing and output with pen plotter, a stereo pair of analog films are set up in a stereo plotter and the operator will manually read terrain features through stereo photogrammetric plotter called analytical plotter.

b. Digital Photogrammetry
In digital photogrammetry, aerial films are converted into digital image data with high resolution (5-25mm). Digital elevation model (DEM) is automatically generated with stereo matching using digital photogrammetric workstation. Digital ortho photo and 3D bird's eye view using DEM will be also automatically created as bi-products. It is still very expensive but only a method for automated mapping. There is a need for futher research for identifying the patterns of houses, roads, structures and other terrain features automatically, that is so called image understanding.

Figure 3.6 shows a digital photogrammetric workstation.