4.11.1. Stereoscopic model

A stereoscopic model can be created with a stereo-pair or stereoscopic images or a stereogram. When two successive photographs taken from two different exposure stations cover part of the common scene which is called a stereo-pair. The 3D model created for the common area to both photographs is called a stereoscopic model or stereo-model.

A stereoscopic model is essentially a three-dimensional representation created from two photographs taken at slightly different angles. These photographs, referred to as a stereo-pair, overlap in particular areas they capture. The overlapping region allows for a 3D effect when viewed together, enabling an understanding of depth and perspective.

Imagine how our eyes work: each eye captures a slightly different view of the same object, which our brain combines to perceive depth. Similarly, a stereoscopic model uses two photographs to mimic this natural process, allowing us to see a '3D' version of flat images just like how we perceive objects in everyday life.

Stereoscopic model thus provides the ability to resolve parallax differences between far and near objects. The 3D view can be created from a stereo-pair through stereoscopic process, using simple equipment, such as stereoscopes or sophisticated equipment, such as stereo-comparator, or digital photogrammetric systems.

Stereoscopic models are advantageous because they allow viewers to discern differences in depth, known as parallax, between objects at varying distances. This functionality is especially important in fields like mapping and photogrammetry. The interpretation of these models can be achieved with both basic tools like stereoscopes and advanced technology like digital photogrammetric systems, making it more accessible for various applications.

Think of how architects use 3D models to see their designs in relation to the surrounding space. Just like a model helps them visualize how a building fits in a neighborhood, a stereoscopic model helps surveyors and engineers visualize landscapes in 3D, enhancing their understanding of geographical features and structures.

Some people with their normal vision in both eyes and having experience in photogrammetry can develop a stereoscopic vision without the use of a stereoscope. Seeing stereoscopically with the eyes without a stereoscope can be practiced with a famous “sausage-link” exercise.

Interestingly, individuals who are adept in photogrammetry can train themselves to perceive depth without specialized tools. One effective exercise involves positioning the hands in a certain way to create an optical illusion of 'extra' fingers, dubbed the 'sausage-link' exercise. This practice enhances one's ability to understand depth and spatial relationships visually.

This can be likened to how athletes practice drills. Just as a soccer player enhances their footwork through targeted exercises to improve their game, individuals can hone their ability to perceive depth by performing specific visual exercises, training their brains to interpret spatial relations effectively.

Hold your hands at eye level about 10 inches in front of you, and select the homogeneous background with a different color than your fingers. Point your index fingers against each other, leaving about 1 inch distance between them. Now look through your fingers, into the distance behind them.

In this exercise, you create a scenario where your fingers appear to create an optical illusion of a third finger (the 'sausage'). This phenomenon occurs when you focus on distant objects rather than your fingers, leading your mind to juxtapose the position of your fingers with the background, creating a perceived depth effect.

This exercise is similar to how a magician uses misdirection to create illusions. Just as a magician directs your focus away from a trick, this exercise encourages you to shift your focus, enabling your brain to process visual information differently, enhancing your spatial awareness in tasks like interpreting aerial photos.

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