Multiple Camera Suspended Rigs

For some purposes, a single camera is not enough. Dual- or even multiple-camera mounts may be used for simultaneous images either in various spectral ranges, with different focal lengths/image scales, or from different vantage points for stereo imagery. Multiple-sensor mounts also may combine cameras with such non-imaging spectral measurement devices as spectroradiometers or thermal-infrared sensors in order to collect multispectral information about the viewing target (e.g. Vierling et al., 2006). Such rigs are by necessity larger in size and heavier than single-camera mounts, which makes flying them potentially more difficult. In order to minimize weight, some functions and extra devices may be omitted as described for selected mounts below.

For simultaneous stereo SFAP, two cameras need to be mounted some distance apart. The length of the boom determines the air base B that together with the flying height Hg control the base-height ratio and thus the amount of stereoscopic parallax (see Chapter 3)—the longer the boom, the better is 3D perception. In the example shown in Figure 7-8, the boom position is always mounted parallel to the kite line or blimp keel, in order to minimize wind resistance, and camera tilt angle is set on the ground prior to

Camera Mounting Systems

FIGURE 7-8 Stereo-mounting system for kite or blimp aerial photography. The boom is ~1m long with cameras (C) at each end. The small dihedral wings (red) are designed to keep the rig parallel to the wind. R, radio receiver; B, battery pack. Total weight of this rig and cameras is ~0.9 kg. Rig built by B. Leffler (California, United States).

FIGURE 7-8 Stereo-mounting system for kite or blimp aerial photography. The boom is ~1m long with cameras (C) at each end. The small dihedral wings (red) are designed to keep the rig parallel to the wind. R, radio receiver; B, battery pack. Total weight of this rig and cameras is ~0.9 kg. Rig built by B. Leffler (California, United States).

FIGURE 7-9 Dual-camera rig for kite or blimp aerial photography. Two SLR film cameras are mounted bottom-to-bottom for simultaneous pictures of the same scene in color-visible and color-infrared formats. Total weight of this rig and cameras is 1.5 kg. Rig built by B. Leffler (California, United States).

each flight. Once in flight, tilt and pan positions of the cameras cannot be changed. Microservos trigger each camera simultaneously to acquire pairs of overlapping images (see Fig. 2-9).

For multispectral systems, two cameras are commonly mounted side-by-side with minimal separation between the lenses. A typical configuration is for one camera to take color-visible or panchromatic photographs, while the other camera takes simultaneous color-infrared images (e.g. Jensen et al., 2007; Verhoeven, 2008). In the example shown in Figure 7-9, camera pan and tilt positions are set on the ground prior to each flight and cannot be changed once the rig is in the air. The camera shutters are triggered electronically to produce dual images of identical scenes (see Fig. 2-5). As the two images are usually to be combined into a single multiband image for analysis, careful mounting of the two cameras is important. Any further separation and any relative tilt between the cameras increase the parallax between the two images, which in this case should be avoided. Multiband imagery may be especially useful for certain applications involving vegetation, soils, and other environmental features.

100 Photography Tips

100 Photography Tips

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