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Mobile app enables detailed 3D mapping of entire buildings

14 January 2016

When Thomas Schöps set out to create a three-dimensional model of the ETH Zurich main building, he used only his tablet computer loaded with a special app.

A 3D model of the ETH Zurich main building, courtesy of Thomas Schöps (ETH Vurich). The red line indicates the path the scientists took in order to generate it

As he completes a leisurely walk around the structure, he keeps the device's rear-facing camera pointing at the building's façade. Bit by bit, an impressive 3D model of the edifice appears on the screen. It takes Schöps, a doctoral student at the Institute for Visual Computing, just ten minutes to digitise the structure of the building.

He developed the software in cooperation with his colleagues from the group led by Marc Pollefeys, Professor of Informatics. Development was carried out as part of Google's Project Tango, in which the internet company is collaborating with 40 universities and companies, ETH Zurich being among them.

The ETH scientists' method works by purely optical means. It is based on comparing multiple images, which are taken on the tablet by a camera with a fisheye lens, and uses the principle of triangulation in a manner similar to that applied in geodetic surveying. Essentially, the software analyses two images of a building's façade that were taken from different positions.

For each piece of image information (pixel), it searches for the corresponding element in the other. From these two points and from the camera's known position and viewing angle, the software can determine how far each picture element is from the device and can use this information to generate a 3D model of the object. The images created even show architectural details such as the arrangement of bricks in a stone façade.

The ETH scientists programmed the software for the latest version of the Project Tango mobile device. "These tablets are still in the development phase and are not yet intended for end users, but they have been available for purchase by interested software developers for a few months now, also in Switzerland, Schöps explains. "The first apps for them have already been developed; however, at the present moment the device is out of stock."

The researchers found the mapping of large objects to be plagued by calculation errors in respect of the 3D coordinates. Differentiating between correct and incorrect information was solved by programming the software to scrupulously delete all dubious values. Real-time feedback is essential to ensuring that the 3D model does not become a patchwork. Thanks to a preview mode, the user always knows for which building areas they have collected enough information and which still require scanning.

The technology could be integrated into cars to allow them to automatically detect the edge of the road, for example, or the dimensions of a parking space. Accordingly, the current project has also utilised findings from the EU's V-Charge project for the development of self-parking cars, in which Marc Pollefeys' group was also involved.

At least one large computer manufacturer recently announced its intention to put a smartphone with the Google Tango technology platform on the market this coming summer.

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