Photogrammetry: let’s step into the space of art objects – virtually

Remote sensing is not a trick of psychics. It is the collective term we use for every method of data collection and processing in which an object, or even a large area of land, is surveyed from a distance, without direct contact. One important technique within it is photogrammetry. As its name suggests, photography plays a key role in it: photographs are taken of the object in question, and then various measurements and calculations are used to determine the dimensions of the object shown in the image.

From maps to art objects

The technique is almost as old as photography itself. In 1858, a young architect, Albrecht Meydenbauer, nearly fell from one of the towers of Wetzlar Cathedral while surveying the building. That was when he had had enough of working at great heights. Instead, he developed a method for determining the dimensions of an object from photographs. The first photogrammetric societies were founded as early as the 19th century. In the 20th century, a great many maps were made from photographs taken from aircraft and satellites, and then high-capacity computers and geospatial applications brought a boom in digital technology to this field as well.

But we should not think that only terrain can be surveyed in this way. Photogrammetry is also a means of acquiring data about buildings and objects. As it does not come into tactile contact with the object, it is perfectly suited to imaging fragile or hard-to-reach art objects. It yields a precise description of the spatial extent, which can be used for archiving and presentation, but also for reproducing the object in question.

Photograph of the original object.

The virtual model with texture (detail).

How is it made?

Besides highly experienced specialists, photogrammetry requires two indispensable tools. On the one hand, very sophisticated measuring cameras; on the other, processing algorithms and a state-of-the-art computing infrastructure.

Of the cameras available today, the Phase One XF IQ medium-format camera is the most suitable for this purpose, as it is the market leader in imaging quality. The digital backs of the Danish manufacturer provide an image resolution of 100 megapixels, 16-bit radiometric resolution and a dynamic range of 15 stops. As a result, the information richness and depth of field of the images produce an astonishingly lifelike picture – indeed, when zooming in, they also provide information that can no longer be seen with the naked eye. The very low noise level of images taken with Phase One contributes to this as well. For spatial imaging, it is also important that the images are taken with suitable overlaps, which requires a rail system capable of precise movements. Then, in the course of photogrammetric processing, a three-dimensional point cloud is generated from the photographs, and an orthophoto that can be regarded as a texture is produced, which makes a wide variety of uses possible.

Detail of the three-dimensional vector mesh.

Detail of the CNC milling paths for producing a carving modelled for the purpose of replication.

What can the data obtained from art objects be used for?

From measuring the parameters of the art object, there is a straight path to the digital archiving of the object, since all the important information about its dimensions and surface is available. This can be stored both as a data set and as a 3D digital recording. But because the object’s physical appearance, surface texture and every small detail of complex shapes are recorded, copies of the object can also easily be made on the basis of the spatial measurement, for example by 3D printing or with milling machines working from the digital model. In the case of art objects that survive only in fragments, virtual reconstruction is also made easier if the surviving parts of the object are digitised in three dimensions. Partially surviving art objects can be reconstructed in three-dimensional space and can also be produced in physical form.

But besides archiving and reproduction, photogrammetry also makes it possible to present art objects, interiors or façades in a spectacular way. The data can be used to create an interactive online interface in which visitors can take a virtual walk. As in a computer game, they can look around the space as if they were there in person. And in the case of smaller art objects, they can walk around them and rotate them, and zoom in on details that they could never see in an exhibition. This is not only attractive to those interested in material culture, but also provides accurate and easily accessible information for scientific purposes, sparing the original object.

Authors: Gábor Bakó, Péter Peti, Boglárka Cziglényi