4.15.3. Types of stereo-plotting instruments

Several stereoscopic plotting instruments have been developed over the past; each with different features. The stereo-plotters can be classified into four groups: (1) direct optical projection instruments, (2) instruments with mechanical or optical-mechanical projection, (3) analytical stereo-plotters, and (4) softcopy stereo-plotters.

This chunk provides an overview of stereo-plotting instruments, which are essential for creating 3D models from aerial photographs. These instruments are grouped into four categories based on their operation and technology. The first group, direct optical projection instruments, utilize simple methods to visualize stereo-models. The second group comprises mechanical projection instruments, which simulate direct projection. Analytical stereo-plotters use complex mathematical approaches, while softcopy stereo-plotters rely on digital images displayed on computer screens.

Imagine a camera that can take pictures in three dimensions, similar to how our eyes perceive depth. Just like different cameras have specific functions, stereo-plotting instruments each have unique technologies to enhance the way we create and analyze 3D models from photographs.

The first-generation stereo-plotters were of direct optical projection design, creating a 3-D stereo-model by projecting the transparency images through projector lenses. The model is formed by the intersections of light rays from corresponding images of the left and right diapositives. An operator is able to view the model directly, and make measurements on it by intercepting projected rays on a viewing screen.

Direct optical projection instruments were the initial technology in stereo plotting. They work by projecting images from two photos onto a single screen, where the light rays intersect to form a three-dimensional model. The operator can directly see and measure the model. This method offers a straightforward approach to achieving depth perception using basic optical principles.

Think of watching a 3D movie where you wear special glasses that help create a sense of depth. Similarly, direct optical projection instruments create a 3D image projected from two different angles, letting the user see a stereo-model directly.

Instruments based on mechanical projection or optical-mechanical projection create a 3-D model from which measurements are taken. Their method of projection, however, is a simulation of direct projection of light rays by mechanical or optical-mechanical means.

Mechanical and optical-mechanical projection instruments represent a significant evolution from direct optical projectors. These devices simulate the direct projection of light rays through mechanical means, allowing operators to view images stereoscopically through a binocular system. This enhances precision in measurements and supports more complex analytical tasks.

You can think of these instruments like a 3D printer that interprets digital data to create physical objects. Just as the printer combines information to produce a tangible item, these instruments combine angles and projections to yield accurate 3D models.

Photogrammetric operations can also be performed by mathematical modelling. This method is called analytical, numerical or computational photogrammetry. With development in optics and mechanics, the analogue photogrammetric instruments have improved to attain high accuracy.

Analytical stereo-plotters leverage mathematical modeling and computer processing to enhance accuracy in photogrammetric tasks. Unlike traditional methods that rely on physical instruments, analytical stereo-plotters calculate object coordinates through complex algorithms. This transition to computational technology represents an advancement in precision and efficiency in photogrammetry.

Consider how smartphones use apps to analyze your photos and add filters to enhance or correct them. Analytical stereo-plotters function similarly, where instead of human hands making adjustments, algorithms and calculations optimize the modeling process.

Softcopy stereo-plotters are the most recent developments. These plotters operate in the same manner as analytical stereo-plotters, except that instead of viewing film diapositives through binocular optics, softcopy photographs are displayed on a computer screen.

Softcopy stereo-plotters represent the latest technological advances in photogrammetry. They display digital images on computer screens, allowing operators to analyze and measure 3D models without the need for physical photos. This shift to digital enhances the speed, accuracy, and flexibility of photogrammetric processes, making them accessible to a broader range of practitioners.

Imagine watching a movie on a streaming platform where you can instantly zoom in or adjust the view with a click. Softcopy stereo-plotters allow you to manipulate and view 3D models quickly and easily in the same way, making photogrammetry more interactive and versatile.

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