The making of the digital twin of the Panorama of the Battle of Murten ‒ EMPLUS ‐ EPFL
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Written by Paul Bourke
The following documents my involvement in the creation of the digital twin to the Murten panorama, namely, managing the scanning process and delivering the final stitched image. With a project of this scale, mine is just one contribution, the others include the staff and students at the eM+ laboratories [1] where the project was conceived and managed, the engineers who designed and built the motorised rig [10], and the historians and conservators on the project.
The painting measures about 10 m high and 100 m long, and exists in three parts, each on a separate roll. The project aimed at scanning it at 1000 DPI (dots per inch) or in metric units, 40 pixels per mm, the approximate width of a human hair. The resulting image, combined, is therefore calculated to be around 400,000 pixels high and 4 million pixels long. It is expected to be the highest resolution digital scan of an artwork. In 2004 a modest resolution (0.5 pixels per mm) digital version was created by Cuno Vollenweider by digitising and manually merging/blending together the photographs taken during the 2001 restoration.
Earlier manually stitched image
For a brief history of the painting, it was painted during 1893-1894 by a team of painters lead by Louis Braun. It depicts the battle between the Swiss Confederates and their allies against the army of the Duke of Burgundy in 1476. It was first exhibited between 1894 and 1909 in custom designed rotunda style buildings in Geneva and Zurich. In 1924 it was put into storage where it stayed until a restoration process was conducted, starting in 1996. The painting was briefly put on display at the 2002 Swiss national exposition, located in a cubic structure on Lake Geneva. Following the exposition the painting was put back into storage within a Swiss mountain facility where it has stayed until 2022 when this digitisation project started. For more information on the history and subject matter of the painting the reader is referred to documentation supplied by the "Foundation [2] for the Panorama of the Battle of Murten".
Restoration
The following are some photographs of the panorama showing how it was previously hung in a cylinder. For practical reasons (size and weight) the full 100 m length was cut into three sections for transport and storage. Each section weighs approximately 1/2 tonne.
Photographs from the 1996-2001 restoration process.
Photographs from the 1996-2001 restoration process.
Photographs from the 1996-2001 restoration process.
Photographs from the 1996-2001 restoration process.<br>Photographs from the 1996-2001 restoration process.Photographs from the 1996-2001 restoration process.Photographs from the 1996-2001 restoration process.Photographs from the 1996-2001 restoration process.
Relocation from storage
The three scrolls were transported from their mountain based storage facility to the eM+ laboratory. The first part of the project was documentation and a conservation exercise, the second stage was scanning for the digital twin.
Relocation from storage
First light
An initial scanning exercise was conducted in order to get a feel for the surface properties and ensure sufficient control points could be acquired for successful stitching. This was particularly important to understand for the sky portion of the painting which may have been quite featureless.
First reveal, scroll 3
First reveal, scroll 3<br>First reveal, scroll 3First reveal, scroll 3
For this exercise a Canon 5D MK III camera, the Canon 100mm macro lens and simple ring light was used. The jury rigged platform was manually moved along an exposed portion of scroll 3 in four columns. Due to the sheer scale of the painting the only viable option was parallel multi-viewpoint scanning [3]. The biggest risk to this approach are parallax issues related to any 3D structures, fortunately in this case the 3D nature was at most 2mm for paint brush structure and didn’t raise any problems.
First exploratory scan, scroll 3
First exploratory scan, scroll 3<br>First exploratory scan, scroll 3First exploratory scan, scroll 3
The resulting 4 columns of the panorama (sky cropped) is shown below. This small test scan was designed so as to result in the same photograph density expected for the final scan. Since the camera was lower resolution the final result stitched to 15 pixels per mm, less than half the target resolution. This confirmed that the characteristics of the painting supported control (feature) point based stitching, however due to the higher glossiness of the sky a cross polarisation arrangement was deemed necessary.
Results from first test scan (32K version only)
An important consideration was how flat the painting would lie on a flat surface. The painting on canvas was originally tensioned on a 30m diameter and 10m high cylinder. This results in the canvas stretching in such a way...