4. Photogrammetry Surveying

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 our world through photos. The term comes from Greek, where 'photo' means light, 'gramma' means drawings or letters, and 'metrein' means measurement. Essentially, it involves capturing images of the Earth's surfaces and environments and then interpreting these images to gather data. This data can then be transformed into maps or detailed information about physical objects.

Think of photogrammetry like taking a series of pictures of a house to create a detailed model. Just like an architect needs various views and angles of a house to understand its shape and dimensions, photogrammetry uses photos from different angles to measure and map the physical characteristics of landscapes.

The conception of using photographs for purposes of measurement appears to have been originated with the experiments of Aime Laussedat of the Corps of the French Army, who in 1851 produced the first measuring camera image for its application to topography.

Photogrammetry began in the mid-19th century with Aime Laussedat, a French army engineer who created a method for measuring land and features using images taken from a camera. His pioneering work laid the foundation for using photography in mapping, which expanded during military applications, especially during World War I, where aerial photographs were critical in creating battle maps.

Imagine being in a war and needing to know the layout of the land to strategize an approach. Laussedat's innovation was like giving generals a superpower by turning photos into tools for planning and measurement, similar to how modern-day GPS allows us to navigate and plan routes effectively.

Aerial photographs which are normally used for mapping and photo-interpretation can be classified into two main categories viz., vertical and tilted photographs.

Aerial photographs can be categorized into two main types: vertical and tilted. Vertical aerial photographs are taken with the camera pointing straight down, which provides a direct view of the landscape beneath. Tilted photographs, on the other hand, are taken with the camera at an angle, which showcases more of the landscape in a single image but complicates measurement due to perspective distortion. Understanding these types helps in choosing the appropriate technique for mapping.

Think of vertical photographs as looking straight down at a city from a tall building—everything is clear and in its exact location. Now, imagine taking a photo at an angle while standing on the same building, you would see more of the surroundings at once, but it may look a bit skewed or distorted. This is the difference between vertical and tilted photographs in photogrammetry.

Photogrammetry has been used in several areas. Some applications are given below. Mapping: The biggest and largest application of photogrammetry is in the field of mapping various features and preparation of various thematic maps, including topographic maps.

Photogrammetry is widely applied in mapping, where it is used to create various topographic and thematic maps. In geology, for example, it helps in mapping structures beneath the earth's surface, while in agriculture, it aids in monitoring crop health and land use. In construction and engineering, it's essential for planning and observing site conditions. With photogrametric maps, stakeholders can visualize important features, improving decision-making.

Imagine trying to build a new highway. Engineers would need precise information about the land they are working on. Using photogrammetry is like having a bird’s eye view of the terrain, allowing them to see where to go, what obstacles exist, and how to design the highway efficiently, just like a gamer looking at a map before making their next move.

The advantages of photogrammetry over the traditional ground surveying are numerous. The photographs provide an economical and efficient way of mapping a large area, no site access issues, provide a permanent record of features at that instant of time; this is especially useful in rapidly changing sites, such as mines, quarries and landfills.

Photogrammetry offers several advantages compared to traditional surveying methods. It is economical, since it can cover large areas quickly and efficiently. Also, it allows one to capture a permanent record of the landscape at a specific time, which is useful for monitoring changes and planning developments. However, it also has disadvantages, such as the need for proper conditions and skilled personnel to analyze the photographs.

Consider a farmer who wants to monitor the growth of his crops. Instead of walking through each row (ground surveying), he can use drones to take aerial images (photogrammetry) of his entire field quickly. This saves him time and effort. However, if it rains or if the drone has a technical issue, he may not be able to get the images he needs when he needs them.

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