Introduction to Photogrammetry Surveying

The Photogrammetry is a surveying and mapping technique which has several applications in the Transportation Department. The practice of Photogrammetry Applications in surveying includes site planning, topographic mapping, earthwork volume estimation for proposed roads, a collection of digital elevation models (DEM), and image-based mapping (orthophotography).

The term “photogrammetry” is the combination of the words “photo” and “meter” it means measurements from photographs. The classical definition of photogrammetry is:

“It is the art, science, and technology of gathering reliable information regarding any physical object and the complete environment.  This technique involves a process of record-keeping, measuring, and evaluating terrestrial and aerial photographs.

Photogrammetry refers to art because to obtain reliable measurements it requires specific skills, techniques, and decisions taken by an individual. Photogrammetry is a science and a technology because it uses images and modifies it, through technology, into significant results. The Modern photogrammetry involves image references and image forms different than photographs, like Radar images.

The photogrammetric process consists of proper project planning, image retrieval, image processing, control data for image adjustment, data accumulation and presentation of an end product results. The result of the photogrammetric method coordinates values of specific points, a realistic representation of the earth surface (topographic map), or a reformed image of the earth surface including map-like characteristics (orthophoto.)

Photographs used for photogrammetry are capture from a special (metric) camera, a typical camera or from digital sensors. The images are captured and recorded from a tool fixed on a satellite, on an aircraft as well as helicopters, or on a tripod (terrestrial photogrammetry) which is set up and mounted on the ground.

Benefits & Drawbacks of Photogrammetry

Here are few Benefits of photogrammetry over standard surveying and mapping methods are as follows:

1. While capturing the Aerial photographs, photogrammetry produces an actual & permanent photographic record of a particular condition that exists while capturing images. Since the record has metric properties, it’s not only a pictorial record, but also it is an accurate, measured record.
2. For information that has to be re-surveyed or re-evaluated, there is no need to perform any expensive fieldwork. The same images we can measure again and can get new information in a very convenient manner. We can quickly remedy the missing information, such as inadequate offsets for cross-sections.
3. It provides a wide mapped area so other line studies can perform with the corresponding data source more efficiently than other traditional methods. Photogrammetry presents a broad view of the project field, by classifying both topographic and cultural features.
4. It is useful in any locations that are difficult, unsafe, or impossible to access. Photogrammetry is an ideal surveying method for toxic areas where fieldwork may negotiate the safety of the surveying crew.
5. A remarkable benefit of photogrammetry is that the road surveys can work without disturbing the traffic by closing lanes, or endanger the field team. Once it captures the roads the analysis of road features, including elevation data, we can do it in the office, not in the actual field.
6. The coordinates of each point in the mapping field can determine with no additional efforts or cost.

The aerial images are useful for conveying or describing information to the public, State, including Federal agencies, as well as to other divisions of Transportation.

Here are some drawbacks:

Climate statuses (winds, clouds, haze, etc.) affect the aerial photogrammetry process and the image quality.

1. Seasonal states affect the aerial images, i.e., snow cover will defeat the targets and defines a false ground impression. Hence, there is only a short-term period typically November through March that is perfect for common purpose aerial photogrammetry.
2. A cleared construction section or a highway that is not blocked by trees is limited to this restriction. These kinds of projects can fly and photograph.
3. Hidden areas caused by human-made objects, such as a roof of a house, cannot map with photogrammetry. Unknown area problems can cause by tree canopy, thick vegetation, or by rugged terrain with sharp inclines. The information hidden from the camera must map with other surveying methods.

The accuracy of the mapping contours and cross regions depends on flight height and the efficiency of the field survey.

The Top Components of Photogrammetry-

In simple words, photogrammetry has three essential components. They are image control, image acquisition, and product compilation.

1. Image acquisition covers planning the overflight, selecting a relevant camera system, photo capturing film processing, film review and annotation, printing of paper copies, and image scanning (if needed.)
2. The Image control component involves the process of selecting areas for ground control and targeting, area surveying control details, and aerial triangulation. This component can get eliminate if advanced GPS methodology can solve the photo orientation difficulty without requiring ground control.
3. The product compilation component varies and depends on the quality of the product. Topographic maps, orthophotos, or monoscopic updates are all photogrammetric products which are organized in many ways as explained later. Each one of these components needs the utilization of various equipment, different measurement techniques, and different data processing.

Conclusion:

A successful photogrammetric survey project depends on a precise understanding of these components, Benefits and careful planning and execution of the project specifications.

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