The Making of Spline

First sketch of curved curtain shapes, February 2017, and photo from Beijing version, October 2017

Concept

In late 2016 i got asked to show my installation Fall as part of the 'Digital Playground Festival' in Bern, Switzerland. Due to communication error, the initial planning assumed a much larger space reserved for the work, and showing Fall in its original dimensions would not be possible. Attempts to scale it down failed, since the ceiling height as the main limiting factor would have made it necessary to shrink it down to 50% or less, whilst still requiring the same vertical distance to the audience, which would distort the proportions too much.

Therefor, a new installation had to be developed, with similarities to Fall, but also essential differences, and suitable for the space available. I wanted to explore further the usage of thin mesh fabric as projection surface for multiple lasers. With such fabric, each single beam of light can pass through multiple layers, creating a high density of dots in a 3D space with relatively little effort. The difference to Fall is the shape of the projection surface. instead of using 180 individual square sheets, suspended from the ceiling to form a fractured 3D grid, I decided to utilise one single curved curtain.

This ensured a different look and behaviour but also reduces setup time. Mounting the sheets of fabric for Fall on thin wires from a large truss high above ground takes days. The single, long curtain, suspended from a curved metal structure promised to be much faster to assemble.

Fall is using two large RYGB laser systems, capable of producing intensive and rich color. For Spline four much smaller lasers are utilised instead, compromising in power, which is not a problem in the smaller space, and in color range, which informed a decision towards a less colourful appearance. Most significantly, we are gaining the ability to have twice the amount of beams emerging from the four corners of the room.

The core concept of Spline is to treat the curved curtain as one single projection surface, with all four lasers pointing at sixteen defined moving spots on that surface. Due to the different positions of the lasers in space and the multiple curves of the curtain, this results in a large number of beam intersections with the curtain.

Patterns and Structure, Sound

The key properties of Spline are the shape of the projection surface, the laser patterns projected at that surface, and the overall structure in time. The smooth shape is constructed in such a way that each laser in average cuts through 5 - 10 layers of fabric, leading to more than 500 intersections between the fabric and the laser beams. The creation of that shape turned out to be unexpectedly difficult. Hand drawings did not create sufficient elegance, and even utilising spline interpolation between randomly created or manually defined sets of points, did not lead to convincing organic yet perfect results. ( My benchmark for such kind of elegance would e.g. be the roofs of the 1972 Munich Olympic building by Frei Otto). After a lot of trial and error, a flower-like shape showed the most promising properties, following a very strict geometric design. The first flowers had 36 knots, deliberately not symmetrical on two axes. However, a simulation of how the beams would cut through the shape showed that the resulting trajectories would not look interesting but simply wrong. The shape got further simplified to its final structure with a strong symmetry matching the laser positions and 32 total turning points. The symmetry of the shape itself does not lead to a symmetrical pattern of laser beams, since each of the lasers hits the same point on the fabric from a different angle.

For Fall, the custom laser control software, which I developed initially for the Lumiere shows has been used. Inspired by Tarik Barri's Versum engine, I embraced the idea to have one modular software environment which 'does it all'.

However, for Spline I departed from that concept again. What I wanted to do with the lasers was simple, but at the same time beyond the capabilities of the Lumiere software. Extending that software was one option, but it turned out to be faster to write a small engine specifically for Spline, with a potential port of some aspects to a future revision of the Lumiere engine. The concept for all movements in Spline is simple: Sixteen objects traverse along the curtain, which is nothing but a warped screen with two dimensions. Each of the objects has a color and a position. The position can be set directly as X,Y coordinates, and each object has its own initial speed vector, friction, and some sort of drift / gravity associated. Colors can be set to an initial value and a decay parameter. A small codebox / gen~ patch in MaxMSP does all that in the audio thread, feeding the lasers with pseudo-audio signals for the X,Y coordinates of the scanners and the 3 colors.

Shape of curtain

This set of options seems very restricted, but in conjunction with the complex projection surface and four distributed lasers, the results can be more than sufficiently intricate and varied.

The overall 'behaviour' of the Spline installation and its look is defined by a set of nested random operations and probabilities, which allow gestures like "explosion", "freeze" , "flow" etc. The result is a mix of predictive behaviour and random coincidences, which I find always very rewarding to experience, since it has an eternal quality to it, unlike a fixed length video loop.

The part of the software responsible for the global behaviour also sends MIDI notes and control data to Ableton Live, to create synchronous sound events, distributed via a 8 channel speaker setup around the visitors. The sonic part of Spline serves three distinct purposes: It enhances the experience of the visual drama, it helps to re-define the gallery/museum space by enveloping the visitor of the installation with a specific sonic aura, and it masks other noise sources such as the fans of the lasers or sounds from other works exhibited near by. The sound very deliberately is not meant to be 'music', it has no meaning in itself, it only works in conjunction with the visual events.

Preparations for bending the spline shape in Bern

Construction and Calibration

For the first exposition of Spline in Bern, a cheap and easy solution for the construction had to be found, which made it necessary to further simplify the shape, moving away from the initial spline based approach towards a structure composed of semicircles and straight segments, which were drawn on the floor at the venue, and then aluminium rods were bent by hand into the right shape, which worked much better than anticipated. Before mounting the curtain, calibration points in regular intervals were added to the metal structure, using fluorescent orange stickers. After mounting the curtain and putting the shape up to the final position, 400 points were manually calibrated per laser - which was tedious and only semi successful.

For the second exhibition in Beijing, China, far more effort went into the preparations of pre-fabricated metal parts, which were assembled on site, forming a new shape with a desired accuracy of less than +-1cm derivation at any point. In practise this precision could not be reached, mainly due to problems with suspending the complete 4,5m wide structure from the 12m high ceiling of the museum without it moving away from the initial position or slightly twisting.

The metal structure from which the curtain is suspended is made of 64 parts, which are connected using screws. This makes it possible to transport the installation easily, despite the large overall diameter. The total length of the curtain is a bit less than 50m and it is 3m wide, resulting in a total surface of 150 square meters.

Instead of manually adjusting the lasers using hundreds of calibration points, now based on the exact shape of the spline, all laser beam angles are calculated using the physical location of the lasers and the spline object: Before mounting the object, each laser unit is adjusted to deliver a perfect square of a certain size, which includes necessary correction curves for nonlinear behaviours of the scanner system, such as the 'barrel' distortion due to the inherent distance between the vertical and horizontal scanner mirror.

As a result of that process, it is be possible to accurately tell the laser which angles to create. Once the lasers and the spline are mounted in their final positions, the relative position between the lasers and the shape is measured, and the lasers are angled at a common center point, serving as reference. This ensures the virtual representation and the real world match, and after entering the measured data points into the software, all four lasers will hit the same spots on the fabric.

'Expressive' curtain shape of spline in Beijing

Beijing Version

The fabric itself has not been ordered in Berlin, but manufactured in China. The material used for the exhibition in Bern could not be found, and an alternative has been suggested by the Chinese production crew, with a more narrow mesh and a different type of fabric. It turned out that the fabric was slightly too thick, and the laser beams did not pass through more than 6 - 7 layers. Unlike expected, the fabric was not delivered on a roll, but folded, and thus we ended up with a very wrinkled and warped shape. These two factors significantly changed the appearance of the work, and thus it has been renamed to "Spline - Beijing Version", reflecting the difference between it and the original. The new version also justified and suggested a change the colors and overall behaviour.

During two nights on site, the installation has been tuned to interact best with the given space and in the larger context of the exhibition. This is a important advantage of works based on generative real time processes. The complete behaviour is created on site, and it is easy to modify the work to match best the situation. Fine tuning the sound, the colors and the speed of movements and overall pace is a essential part of adapting the work for each individual exhibition.

Technical Setup

Spline uses four LaserAnimation Sollinger Phaenon Accurate lasers, which are small precise RGB lasers using the digital AVB protocol instead of the older analogue ILDA connectors. The lasers are connected via Ethernet to a AVB hub, which itself is connected to a MacBook Pro running the Spline software - a custom MaxMSP patch written by the artist, and a Ableton Live set for the sound. A Motu Ultralite interface is sending nine channels of audio to the powered speakers; eight for the ring around the audience, and one for two subwoofers. A fog machine is controlled from the spline software, connected via a USB to DMX interface.

The installation can be turned on and off using a custom switch box, based on a Teensy CPU. Studio Robert Henke made several of these boxes for installations. They consist of two buttons and two status LEDs, which can be programmed to provide various types of visual feedback and possible interactions, like a 'sleep' state or a more hidden ability to control the volume by pressing the on and off button simultaneously for 3 seconds to enter the 'volume' mode. The box allows the museum staff to perform essential tasks without the necessity to access a computer.

Prototype LaserAnimation Sollinger Phaenon Accurate lasers for Spline in Bern