Technologies: Photogrammetry and Laser Scanning

Documenta makes use of the latest photogrammetric and laser scanning technologies, utilizing the most appropriate methodology for each individual project, budget and schedule.

1 - Photogrammetry (noun) [International Scientific Vocabulary]: First appeared in 1875; The science of making reliable measurements (recording) by the use of photographs.

What is Digital Architectural Photogrammetry?

Digital Photogrammetry is a methodology used to produce precise information, plans and maps directly into CAD through photographic measurement, with the assistance of algorithmic computer restitution. 

The use of photogrammetry for applications other than aerial mapping is called close-range or architectural photogrammetry.

Our professional services with digital close-range photogrammetry revolutionize "as-is" or "as-built" surveys because of the time and cost savings we offer, in addition to remarkable accuracy and reliability.

How Does Photogrammetry Work?

Documenta  makes use of calibrated cameras (digital and analog), digitizers, computers and multi-image restitution software(s). For applications requiring exceptional high-accuracy and reliability, our surveying cameras have built-in grid glass plates (reseau) mounted in front of the film plane.

These glass plates have a series of small crosses, with coordinates calibrated to 1/10 of a micron. We use these coordinates to correct film and optical distortions on the photographs. Then, through powerful computing capabilities, the precise camera position in each picture is calculated by way of several algorithms and statistical evaluation of data quality.

We utilize an algorithm called "bundle adjustment", heart of modern digital photogrammetry and developed for high-precision applications. In it, on a final calculation, all computed positions, distances, coordinates, and levels are simultaneously adjusted according to any additional controls and constraints our experienced analysis indicates appropriate to use, and to a theoretical optical model (central projection theory).

With determination of the precise situation of the camera or cameras in each photograph (camera stations), we can locate the exact position where rays traced from these camera stations meet. Depending on the application, we use a minimum of five rays (five pictures) to ensure the targeted accuracy at any given point. 

Finally, in the process called restitution, extremely homogeneous and precise 3D dimensional data is obtained from digitized points in the photographs, allowing for the production of technical drawings. Further, the CAD/GIS interface allows for the thematic layering of the "as-is" information and further modeling, querying, and visioning when required.

2 - Laser Scanning: makes use of newly developed medium range scanners to "scan" a building, monument, structure, or historic resource.

How Does Laser Scanning Work?

The technology utilizes pulsing laser beams which  are systematically sweep over an object to obtain X, Y, Z coordinates of points on it's surface. As the scanned points accumulate, they form what is called a "point cloud" which looks like a computer rendering of the object. All points on a "point cloud" have their accurate 3D position established on a coordinate system. 

Point clouds can be used directly for point-to-point measurements or for 3D visualization. 

With our experienced architectural & engineering interpretation, they are converted into 3D models, 2D drawings (elevations, plans, sections, etc.), that are adequate for each different utilization (remodeling, restoration, monitoring, etc.).

What is more important, Documenta will utilize the most efficient methodology or the association of both, to efficiently and economically document the "existing conditions" of a building, structure, or site. 

Our emphasis is on to obtain the 'right information' and deliver it on the most appropriate format and ready for use.

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