4.1. Introduction

The name “photogrammetry" is derived from the three Greek words phot which means light, gramma which means letter or something drawn, and metrein, the noun of measure. The photogrammetry is defined as the art, science and technology of obtaining reliable information about physical objects on the earth’s surface and its environment, through processes of recording, measuring, and interpreting photographic images.

Photogrammetry combines art and science to gather information about real-world objects and environments using light. It involves recording images, measuring dimensions, and interpreting the data gathered to create useful representations, such as maps or models. The name itself is rooted in Greek, highlighting the foundational elements of light and measurement in this field.

Think of photogrammetry like taking a photograph of a friend standing in a park. Just as you capture their image, photogrammetry captures images of landscapes or structures, allowing you to understand their dimensions and shapes. This is similar to how a sculptor uses sketches to create a statue.

Photogrammetry discipline, like other disciplines, is constantly changing and developing. Presently, it is dependent on developments in data products, computer software and semi-auto or automatic processing methods.

The field of photogrammetry is always evolving due to technological advancements, particularly in computer software and data processing techniques. This means that the methods used to capture, process, and analyze images continue to get better and faster, leading to more accurate and reliable results. Automation plays a significant role, enhancing the efficiency of photogrammetric work.

Imagine how photography has evolved from film cameras to smartphones with advanced sensors and apps that can instantly edit images. Similarly, photogrammetry has progressed, leveraging computers to automate tasks that used to be done manually, making the process faster and more precise.

Images used in photogrammetry are captured from a special (metric) camera, or from digital sensors, mounted usually on aerial platforms or drones. These images can also be recorded from a device mounted on a tripod kept on the ground, called terrestrial images.

Photogrammetry relies on capturing images using specific cameras that can be mounted on various platforms. Aerial platforms, such as drones or airplanes, enable the collection of imagery from above, while terrestrial images can be taken from the ground. Each method provides different perspectives and data, contributing to the overall photogrammetric analysis.

Picture having both bird's-eye views and sidewalk views of a city. A drone captures the bird's-eye view of buildings, while a camera on the ground shows street details. Together, these different perspectives provide a comprehensive understanding of an area.

The acquisition of photographs consists of project planning, image acquisition, image processing, and derivation of results.

Photogrammetric work involves several steps: planning the project to determine what images are needed, actually capturing the images in the field, processing these images to extract useful information, and finally deriving results, which might include maps or 3D models. Each step is crucial for the success of the project.

Think of this process like preparing a school project. First, you plan your topic (project planning), then you gather your materials (image acquisition), work on assembling your project (image processing), and finally, present your findings (derivation of results).

The end product from the photogrammetric process can be the coordinates of individual points, a graphical representation of the ground surface (topographic map, thematic map, etc.), or a rectified image with map-like characteristics (ortho-photos) or a digital elevation model (DEM) or digital maps.

The results of photogrammetry can range from precise coordinates of specific locations to comprehensive maps and digital models that represent the terrain's surface. These outputs are useful for various applications, such as urban planning, environmental monitoring, and mapping.

Just like a treasure map that tells you where to find hidden gems in a park, photogrammetry creates maps that help people locate and understand different features in the landscape. The coordinates act like the 'X marks the spot' for specific points, making it easier to navigate.

The most common use of aerial photographs is the creation of base maps for various applications, selection of ground control points (GCPs), and ground truth verification.

Aerial photographs have wide-ranging applications, including creating foundational maps for navigation, defining reference points on the ground (known as ground control points), and ensuring the accuracy of geographical data. These applications are essential in many fields, such as urban planning and environmental research.

Consider how a blueprint is used to build a house—it provides the foundational reference for construction. Similarly, aerial photographs serve as blueprints for understanding and mapping landscapes, ensuring that everything is built accurately according to the real world.

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