Photogrammetry

Photogrammetry is a scientific discipline that aims to obtain, measure, and interpret reliable information about the positions, shapes, and other characteristics of surfaces and objects without physical contact with them. The term is derived from the combination of three Greek words: “phos” or “phot” (light), “gramma” (something written or drawn), and “metrein” (to measure). In this context, photogrammetry essentially means “measuring with light.”

Historical Development of Photogrammetry

Photogrammetry has evolved through four main generations in line with technological advancements:

• First Generation – Pioneering and Experimental Period: The foundations of photogrammetry were established with the invention of photography.
• Second Generation – Analog Photogrammetry: This period is characterized by the use of stereoscopic images and the development of the first stereo plotting instruments.
• Third Generation – Analytical Photogrammetry: This era saw the application of mathematical models facilitated by the use of computers.
• Fourth Generation – Digital Photogrammetry: With the widespread availability of digital imagery, software-based systems became prominent, enabling automated analyses.

Types of Photogrammetric Information

Photogrammetry classifies the information obtained through remote sensing into four main categories:

• Geometric Information: This pertains to the three-dimensional position and shape of objects. It constitutes the foundation of photogrammetry and is considered the most crucial type of information.
• Physical Information: This relates to the spectral properties of electromagnetic radiation. It is utilized, for example, in object identification based on reflectance characteristics.
• Semantic Information: This involves the interpretation and classification of visual data to understand what the objects are.
• Temporal Information: This refers to the changes in objects over time and is derived from the comparison of images acquired at different dates.

Types of Photogrammetric Products

Photogrammetry processes data acquired through the recording of electromagnetic radiant energy to produce various outputs, which are generally grouped into three categories:

• Photographic Products: These include mosaics derived from individual images or overlapping photographs. Products such as orthophotos fall into this category.
• Computation-Based Products: These comprise three-dimensional point clouds and coordinate data obtained through processes such as aerial triangulation.
• Maps: These are the most commonly known photogrammetric products, produced at various scales and accuracy levels.

Tools Used in Photogrammetric Processes

Throughout history, various tools have been utilized in photogrammetric processes during different periods, including:

• Photographic rectifiers
• Orthophoto projectors
• Comparators^【1】 
• Stereo plotting instruments
• Analytical plotters
• Digital (softcopy) workstations

Today, most of these tools operate digitally in software-based environments.