Creating Simple OnScreen Stereoviews

Lack of 3D impression is not something you want to discover after producing a series of A4-sized glossy prints or having spent days on a photogrammetric triangulation project. Before choosing an image pair for printouts, anaglyph creation, or photogrammetric analysis, it is useful to assure oneself of its stereoscopic quality. Even with a decent overlap, which is easy to assess in monoscopic view, the stereo impression might be unsatisfactory owing to unfavorable image tilts or differing scales, both typical situations for SFAP. The latter may be remedied by scaling one image to fit the other prior to printing them, but the former can only be cured by choosing different stereopairs.

Simple freeware image viewers (e.g. IrfanView) are useful tools for such checks (Fig. 11-19). Opened side by side, the images can be scaled and rotated following roughly the orientation procedure described above. With a little

FIGURE 11-18 Relatively orienting two images for stereoscopic viewing. Step 1: identifying the image centers o (by using the image corners) and their corresponding points o' (by using the image contents). Step 2: rotating both images so all points lay on a horizontal line parallel to the eye base; 3D viewing is possible in the stereo-area shaded in gray.

FIGURE 11-18 Relatively orienting two images for stereoscopic viewing. Step 1: identifying the image centers o (by using the image corners) and their corresponding points o' (by using the image contents). Step 2: rotating both images so all points lay on a horizontal line parallel to the eye base; 3D viewing is possible in the stereo-area shaded in gray.

FIGURE 11-19 Two vertical aerial photographs of Barranco Rojo near Botorrita, Province of Zaragoza, Spain, oriented for stereoscopic viewing on a computer screen. The right image has been rotated and slightly enlarged to match up with its stereopair. The parallel-eyes method may be used to view this scene in 3D. Hot-air blimp photographs by IM and JBR, April 2006.

FIGURE 11-19 Two vertical aerial photographs of Barranco Rojo near Botorrita, Province of Zaragoza, Spain, oriented for stereoscopic viewing on a computer screen. The right image has been rotated and slightly enlarged to match up with its stereopair. The parallel-eyes method may be used to view this scene in 3D. Hot-air blimp photographs by IM and JBR, April 2006.

practice, the parallel-eyes method (or, if preferred, the cross-eyed method) is quite helpful for selecting the optimal images from a survey series.

Even more convenient are stereoviewing tools that allow the user to rotate and scale the images for relative orientation and then offer the choice to display them for parallel-eyed, cross-eyed, anaglyph or even shutter-lens viewing. A variety of useful freeware is available on the Internet (e.g. StereoPhoto Maker).

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