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Making-of 1850 Geneva in 3D

Scanning the Relief Model of 1850 Geneva

Digital immortality for the Relief Model of 1850 Geneva

Designed and built between 1878 and 1896 under the direction of the architect Auguste Magnin, the Relief Model of 1850 Geneva is more than just a spectacular model, a masterpiece of goldsmithery. It is also a representation of fortified Geneva at a key moment in its history. In 2010, the decision was made to create a digital 3D copy of the model so that it could be reproduced in case of eventual damage. The 3D model could also be exhibited in museums and even be used to facilitate the work of surveyors – for example, to locate areas where excavations of todays’s Geneva might risk hitting the old barrier walls. But, to do so, of course, the model would have to be absolutely precise.

The Relief Model of 1850 Geneva is housed in the attic of the Maison Tavel (Geneva’s oldest private house, now a museum) so, first, the engineers had to make sure that the floor was perfectly stable. For a week, they observed the building’s movements using a high-precision theodolite. Once the measurements proved it to be stable, they were able to begin their work, while continuing to monitor the building for vibrations.

Outcome of scanning: a cloud made up of millions of points

To avoid damaging the Relief Model, the engineers installed a gantry over the miniature city to position a scanner and a camera. They also gently placed 1,268 tiny markers throughout the model as landmarks. The scanner yielded a cloud of 120 million dots referenced in space - as if a mold of the Relief Model had been made using a fine mesh with an accuracy of one-tenth of a millimeter. The camera produced 1,280 high-resolution images, all perfectly identified according to orientation - enough to recreate the entire Relief Model.

Months of work were then necessary to extract from this cloud of points and photographs a precise 3D model of the Relief Model of 1850 Geneva. Using specially developed programs, the engineers defined the edges and angles of the three rows of fortifications, as well as some 2,000 buildings and their 40,000 windows and 8,000 skylights - not to mention fireplaces, staircases, fountains, trees and other countless details making up the miniature city. At last, the entire Relief Model was reproduced as a 3D digital model faithful to the work of its creator.

Adjustment of a 3D building on the cloud of points

3D model of the College de Genève based on an architectural drawing by Auguste Magnin

A masterpiece of geometric precision

In his numerous tests with cardboard models, Auguste Magnin discovered that the best method for creating his Relief Model of 1850 Geneva was to use three different reduction scales: 1/250th for the floor plan, 1/200th for the heights of the buildings and 1/100th for the slopes of the terrain. This choice, due to aesthetic and educational criteria, obviously distorted the buildings and topography, especially for districts built on the slope. Because of these geometrical deformations and because it has until now been difficult to take precise measurements on such a vast and fragile model, Auguste Magnin’s Relief Model was never considered to be a tool for urban planning. However...

The finished model of the College

When they began working on the Madeleine district of the Relief Model, which includes still existing buildings and a church, the engineers discovered that they were dealing with an exceptional model. When they reduced the three scales to their right proportions, enlarged the district and placed it in the official cadastre of present-day Geneva (the three-dimensional Geneva Territorial Information System, SITG), they had a wonderful surprise. The gaps between the enlarged model and the real buildings are of the order of 1.50m - minor for such an enlargement!

Auguste Magnin had not only created a masterpiece of art, but also a masterpiece of precision, given the instruments of his time. Although the engineers still have no idea how the architect was able to achieve this feat, they quickly realized that they could use the

Old drawing of the College de Genève

model to produce a complete 3D model of 1850 Geneva based on the Swiss national coordinate system. Even better, they could recreate the walled city virtually, making it available to the public for visit on the Internet.

To help them in their work, they could rely not only on scanner data and photographs, but also on the tens of thousands of archival images held in the Iconographic Center of the Geneva Library (CIG) - old photographs taken in the streets of Geneva in 1848, plans and drawings made by Auguste Magnin himself of remarkable buildings, engravings and paintings of the time, as well as 19th century topographic plans and cadastres. All potentially useful material was carefully scanned by the CIG.

Putting the Relief Model of 1850 Geneva on the official cadastre

However, no computer software existed able to take into account the three scales of the Relief Model of 1850 Geneva, bring them back to their right proportions, enlarge all the elements of the model and, finally, match the whole to coordinates of the national map of Switzerland. So, most of the programs needed had to be written. One particular problem the engineers confronted was the difference in scale between the slope of the land and the height of the buildings.

Control of the adjustment of city blocks and buildings

To accomodate the steepest streets of his model, Auguste Magnin had split the alignments of buildings into several sections; thus, contiguous buildings in the model have roofs like staircases, whereas the real rooflines are continuous. To digitalize the city, engineers had to work facade by facade to avoid giving their model windows that were diagonal or doors half-buried in the ground.

Control after correct sizing of the model’s three reduction scales

It was also necessary to adjust certain defects in the alignment of the 118 blocks that make up the Relief Model. Auguste Magnin made his 30m2 model in several parts that were then assembled. He did this for two reasons: first, to facilitate the minute work of the craftsmen who shaped the buildings, and, second, to make it easier to move the model, weighing 680 kilos. But, as the Relief Model has been dismantled and rebuilt several times since its completion in 1896, the edges of the blocks have suffered and today’s junction is not ideal.

Each block of the miniature town, therefore, had to be treated separately, street by street, building by building. Although a large part of operations could be automated, many details and fittings had to be adjusted by hand. Without the help of historians who specialize in Geneva’s monuments, the engineers would not have succeeded. Invaluable help also came from their colleagues of the 19th Century: the engineers consulted such works as the “Céard Map” of 1840, 30 detailed maps at 1/240 scale drawn by the surveyor François Janin, and the “Album des monuments de Genève en 1850”, an entire series of maps and magnificent architectural drawings drawn by Auguste Magnin himself.

Model of a quarter of 1850 Geneva before details were added

In all, 16 months were required to digitalize the 118 blocks of the Relief Model, to check them, have them validated by the official cadastral survey office and, finally, to transfer them to the cadastre of Geneva. The result is a complete model of 1850 Geneva in 3D, based on the model of Auguste Magnin, perfectly integrated into the numerical model of the territory and the official cadastre. So, it is possible to see which buildings or parts of fortifications have disappeared, which have been transformed and which are still intact. It is also possible now to know where parts of the thick walls remain buried underground, relics of the filling in of the city’s moats that began in 1850.

Adding texture to a group of buildings

Breathing life into the 1850 Geneva Relief Model

The 3D model of 1850 Geneva is a blank, featureless city, without texture or color, as if cast in plaster. To give it atmosphere in keeping with its time took the collaboration of specialists from several disciplines - geometers, geomaticians, historians and 3D designers.

First, the specialists built a documentary base to create their materials, looking for elements of construction little changed since 1850 - paving stones, tiles, plaster, doors and windows, etc. - and photographing them from every angle. In total, some 50 materials were recreated numerically. Each material was then given three variations of deterioration: clean, slightly dirty, worn. In addition, subtle variations were added randomly to prevent the virtual city from looking too uniform. Specially developed computer algorithms facilitated this repetitive work, but the tight, connected buildings of old Geneva offer many special cases and, for the sake of detail, the specialists had to do much of the work “by hand”, keeping an eye on the iconography center’s precious archival images.

The varieties of trees and other vegetation that grew in the city and on its walls were selected with the help of botanists from the Geneva Conservatory and Botanical Gardens based on documents of the time.

Photo of the city gate Porte de Neuve in 1850

Virtual landscape of 1850 recreated around Geneva

Setting 1850 Geneva into its historic landscape

As the 3D model of 1850 Geneva took on color, the specialists soon became convinced that the fortified city would be much better if set in the landscape of its time. The mountains were not too difficult to reconstruct: the Jura Range, Salève and nearby Alps have scarcely changed since 1850. However, a large part of the sparsely populated countryside that once surrounded Geneva has been urbanized.

Here again, the problem was overcome thanks to a colleague from the 19th century, Jean-Rodolphe Mayer. Between 1828 and 1831, this surveyor mapped the entire canton of Geneva on a scale of 1:15,000, indicating in detail not only buildings, roads and rivers, but also the nature of the land: fields, forests, vineyards, gravel pits, meadows, gardens, etc. Period engravings and paintings served as additional sources of information. The work was greatly facilitated by the immense resources of the Geneva Territorial Information System (SITG), containing many historical maps perfectly aligned with modern topography.

To render the landscape of 1850 Geneva, the specialists did not take the easy path: all the elements close to the city walls are in 3D. Based on the advice of botanists, hundreds of thousands of 3D trees and bushes were “planted”. As for the blades of 3D grass, they number in the billions...

Four views of Bastions Park: old engraving, 19th century photo, model made by Auguste Magnin and modern 3D Model

Four views of Bastions Park: old engraving, 19th century photo, model made by Auguste Magnin and modern 3D Model

Preparing 1850 Geneva for a walk on the Web

As the 3D model of 1850 Geneva was being dressed up through virtual reality, a team of computer scientists were working on the tools that would be necessary to visit – on the Internet – the ancient walled city. Named PromenAdd, this original technology deploys both real-time 3D (as used in video games) and pre-calculated 3D (as used in cinema).

For the virtual visit, the user does not need to download software: an ordinary computer, with a standard connection speed, is sufficient. Moving around the city is a bit like browsing in Google Street View. However, in the model of 1850 Geneva, the steps are much shorter and the images are better defined. And one can even hover in the sky to enjoy a view overlooking the city and its surroundings. In total, the surfer can walk along 1,333 paths and stop at 963 crossings offering as many points of interest.

An Internet user walking through the streets of 1850 Geneva sees some 200,000 different views. To generate all these high-resolution images from the 3D model, 16 powerful servers worked for six months - a workload comparable to producing two Hollywood movies in 3D. The light chosen to illuminate the walled city and its surroundings is that of a summer morning in June at 10 am.

1850 Geneva seen from the lake

A big step forward in the digital humanities era

As one might imagine, the 3D model of 1850 Geneva differs from historical reality, being based largely on the model made by Auguste Magnin. It is a pristine city, (for now) depopulated, whose buildings have a somewhat uniform appearance, particularly the doors, windows and chimneys. To get a better idea of the city of the time, one must look at photographs of the 19th century: the houses blackened by coal smoke, the often dilapidated facades with advertisements, the streets cluttered with merchandise and drying linen, the cobbled-together wooden out-buildings for increased living and work space. Nevertheless, the 3D model offers a good idea of the walled city of 1850 and its surroundings. It is a solid documentary base capable of evolving towards greater historical reality, a step into the Digital Humanities era, this new field of research, engineering and teaching that combines the humanities and technology to disseminate knowledge.

View of 1850 Geneva with navigations icons

Into the virtual world of 1850 Geneva, one can add old photos, texts and commentary… Making all sorts of information available at the very spot where it needs to be found

Next step: a 3D wiki around 1850 Geneva

Having formed the gE-story Association, the main participants in 1850 Geneva project do not want to stop here. Once they have funding, they plan to adapt Internet tools to allow authorized contributors to add to the city’s décor, adding all kinds of information linked to the history of its sites and to the development of urbanization – starting with the thousands of images waiting to be made use of in the archives of the Iconography Center of the Geneva Library (CIG). When that happens, the website www.geneve1850.ch will make Internet history, showing that it is possible to create a sort of 3D Wikipedia where information is found in its natural place, where one can navigate freely through documents that take you to the virtual space concerned, and where browsing is open to all – without the need to download any particular software.

A small step has already been taken: in the streets and along the walls of 1850 Geneva, one can already access some hundred explanatory sheets (in PDF format; for now, only in French) to obtain historical information on the most interesting buildings and artworks. A final note: the list of these remarkable monuments was drawn up by Auguste Magnin himself.

Old photo

1850 Geneva model in 3D

Comparison between an old photo and the 1850 Geneva model in 3D