Old Prague to come to life in 3D computer model

Photo: M.Fokt

Looking at old photos of quaint parts of downtown Prague that were demolished at the turn of the 19th century to make way for fashionable apartment blocks, one easily gets nostalgic. But thanks to modern technologies, one day soon it will be possible to walk through the streets and lanes of the old Jewish quarter of Prague - but of course, only in virtual reality.

Antonin Langweil
One of the most precious exhibits at the Prague City Museum, a realistic cardboard replica of old Prague, meticulously put together by a library worker named Antonin Langweil in the first half of the 19th century will soon be available in digital form. The digitisation process is now underway right at Prague's City Museum where the Langweil model has been displayed for decades.

"The decision was made at the end of 2005. A year later we held a tender for the job - and the winner was the Prague company Visual Connection. On top of that, we have a number of expert consultants - we own the model but we don't understand modern technologies."

...says Zuzana Strnadova, director of the Prague City Museum. The Langweil model is believed to be one of the most detailed models of a city in the world. It is also the most popular exhibit in the museum.

"There are over 2000 houses on the model. It includes Prague Castle, Mala Strana or the Lesser Quarter and The Old Town complete with the Jewish district of Josefov which was later demolished. The whole model is made up of 52 parts which are assembled together. Every time we take it apart we need to call the restorer, Mr Bouda who knows how to disassemble it and put it together again. We hope he has now passed his knowledge onto his son."

On the first floor in the museum, there is a kind of dark chamber where a camera suspended from a metal frame is taking photos of one part of the Langweil model. Jan Burianek from Visual Connection, the company which is carrying out the digitisation, describes the process.

"There is a special capturing station here. It is a robotic-based system for capturing data for a digital Langweil model. It is a special kind of robot which uses quite a sophisticated movement system, including a special kind of CCD (Charge-Coupled Device) sensor for capturing data visually from the 3D model of Langweil. We cannot touch the model but we have to measure the data for a future 3D reconstruction of the model."

"What we can hear now is the sound of a special kind of shutter and a flash lamp which is using a special kind of macro lenses. It uses sixteen megapixels of precision and high dynamic range pictures for measurement of light and textures and geometry. We will get more than half a million of such pictures from that device. We will use that for a 3D reconstruction of the whole 3D Langweil model. It will take probably more than two months for twelve hours per day to do that."

"We will need the next eight months to process the data and use a 3D reconstruction method from computer vision and near close photogrammetry to get the 3D model including geometry and textures. That's our goal and the resulting data will be something like 12 terabytes of data, let's say 3000 DVDs and finally we will get quite precise 3D model, 3D measurements for scientists and people from the museum and we will also make this data available to the public. It means that it will be presented for the public but in lower resolution because it is not possible to use just a standard method to present it and it will probably be available next year during the spring."

In the meantime the camera keeps taking photo after photo. You feel like you are in the middle of a science fiction movie - a robotic arm is looming over a city taking photographs from all angles. The smallest details, only slightly larger than a pinhead, are photographed by a medical camera normally used to probe the human body. All this has to be done very sensitively because, for example, normal photographic flash light might damage the old fragile material.

The project of digitisation of the Langweil model is financed by the Prague City Hall. Pavel Bem is the Mayor of Prague.

"It is an absolutely unique and excellent model of Prague from the first half of the 19th century. It was designed by Antonin Langweil between 1826 and 1837. So if you imagine that such a model on 20 square metres offers the perspective and sort of a mirror what the city of Prague, the old historic centre with Jewish Ghetto, Mala Strana and Hradcany, looked like almost 200 years ago. Then you can imagine the real uniqueness of such an exhibit. The digitisation of the model is another step how to deliver a product which will be used by experts in the cultural heritage protection department but which will also be definitely extremely attractive for tourists, visitors, children, school pupils who definitely could see the real life of the city almost 200 years ago."

Do you have any personal memories of the model? Did your parents take you there to see it as a child?

"Yes, yes. My mother was a very big fan of the Langweil model. My grandfather from the maternal side was almost an expert on the Langweil model. I saw it as a little kid several times, but frankly speaking, it is really a 200 years old exhibit in the Prague city museum, so it doesn't really offer sort of a modern attractive perspective. You don't see too much and one of the reasons why we decided to digitise the model is really to increase the attractiveness."

Almost two hundred years ago, Antonin Langweil needed paper, glue, colours and lots of skill and patience to create his minuscule but giant work. Today experts on robotics, computer vision and computer graphics are working with the latest technologies to preserve the model for posterity in a virtual 3D form. Prague councillors who approved the digitisation project say they can even envisage computer games taking place in the narrow lanes of old Prague - sparking an interest in children abroad who one day might want to visit the Czech capital for real.