Fly-Line Ruhpolding: When a real ride becomes a virtual one . .
About 500 meters through the forest, a VR headset on your head and a virtual world that unfolds exactly in line with real movement – developed for the Fly-Line Ruhpolding in the Unternberg region.
Walk through the forest – about half a kilometer long
Pico headsets in daily operation on site
Presentation modes in an experience: VR, mixed reality, immersive video
Chapter: interactive departure and narrative mountain tour
The Fly-Line Ruhpolding in action
A ride that feels like floating
The Fly-Line Ruhpolding am Unternberg runs through the forest on a 500-meter-long track. Guests sit in a system suspended below the guide rail and glide down numerous curves. Unlike a zipline, maximum speed is not the focus – the ride is calmer and provides the feeling of floating through the forest.
The idea: To develop an additional experience world from the existing ride. Guests wear a VR headset and travel through a virtual environment while moving through their real world.
The special advantage: Physical motion provides what classic VR has to painstakingly simulate—real acceleration, real curves, and actual movement through space.
Before departure: The VR glasses are on, the real driving begins immediately.
Virtual and real movement must match
In a stationary VR application, the movement can be fully controlled in the virtual world. In the Fly-Line Ruhpolding, the real facility provides the movement.
When the body perceives a curve while the virtual world is traveling straight ahead, a contradiction arises between sense of balance and perception – and thus quickly leads to motion sickness.
How can we reliably determine at any time where a passenger is located on the fly-line – regardless of daylight, shadows, vegetation, and weather?
Five steps to a position determination that works in the forest
The five points show different tasks and approaches: Step 1 is the foundation – the digital model of the track. In steps 2 to 4, we tested tracking variants under real conditions and discarded them for various reasons. The inside-out tracking of the headset repeatedly lost its spatial positioning in the forest and in bright sunlight: branches and leaves offer few stable, unambiguous image features; similar structures, motion, and alternating light and shadow further complicate orientation. Step 5 describes the magnetic reference system used.
The real route will be digitalized
A body-borne XGRIDS L2 Pro LiDAR scanner captures the entire route as a point cloud during a journey. In Blender and 3ds Max, this creates a centimeter-accurate digital twin of the route – the geometric reference for development in Unity.
Inside-out tracking in the forest
Inside-out tracking uses SLAM and requires distinctive, reliably recognizable image features. In the forest, leaves and branches are similar; they also move constantly. Sunspots, shadows, and strongly changing brightness constantly change the camera image. The headset repeatedly lost its spatial positioning – in the forest as well as in bright sunlight. The position was out of focus or could no longer be stably associated with the actual travel. Filters in front of the cameras did not sufficiently improve the result.
ArUco markers as reference points
Contrasting ArUco markers initially improved tracking, but they significantly responded to light conditions: in the morning, the detection worked well; after noon, it was noticeably less effective in diffuse light. Around 100 markers would have been needed for the entire route. The trees would have visibly disrupted the natural forest landscape and would have been visually very present to the guests. Thus, the approach was neither reliable nor suitable for continuous use on site.
Mechanical measurement
A measuring wheel that runs along the guide rail should mechanically record the distance traveled. For this to be possible, the wheel would have had to maintain permanent contact with the tube. During the design review, it was revealed that this contact—especially in curves and transitions—could not be reliably ensured. Even a single loss of contact would have interrupted the distance measurement and jeopardized the synchronization of the virtual world with the driving. Therefore, after careful review, we already discarded this approach in the concept phase and did not further test it.
Magnetic reference points along the route
Our solution: Strong magnets are located at selected positions. A specially developed sensor on the moving system detects them when they pass by and reports them to the VR application – real checkpoints, independent of sun, shade, leaves, or cloud cover.
The software decides which signal it trusts
During longer test days, magnetic interference signals appeared along the steel structure – especially in the afternoons, at locations without a magnetic field. The first sensors only provided „detected“ or „not detected“ readings and sometimes considered the interference to be real reference points.
So the sensor became a measurable measurement system: The raw data were recorded, visualized, and compared with the set magnetic positions over many test drives. The breakthrough lay in the signal pattern.
„Robustness does not necessarily result from a perfect sensor – but from the fact that sensor technology and software work together to decide which data can be trusted.“
From binary to measurable
Instead of a yes-no signal, the sensor software reads real measurement values – for the first time, it becomes visible how the reference value and the disturbance differ.
Context-dependent tracking
A signal that is measurable but does not match the expected course of the journey is ignored. This ensures that the system is stable enough for operation.
Not just VR or mixed reality – but both
During the descent, the headset's position tracking no longer affects the virtual position: The glasses operate largely with 3 degrees of freedom, the head movement remains free. The Pico 4 Ultra Enterprise It is allowed to control tracking functions specifically from the application – and thus switch between the modes depending on the section.
Full VR
The real Fly Line disappears behind the virtual world. The position along the route is provided by real movement and magnetic checkpoints.
Mixed Reality
For safety reasons, guests once again see their real surroundings as they enter. The passthrough view becomes part of the staging – the story continues.
Immersive video
During the approximately five-minute ride, a pre-produced 360° video is already running, which recounts the legend of the Rauschberg Mandl. The camera movement and the image movement are adapted to the actual ride: The virtual forward movement follows the actual ride. In this way, both movements complement each other to create a calm, harmonious overall experience, rather than working against each other.
A journey through the world of the Rauschberg almonds
Not just any fantasy world: The experience is based on a local legend. In the region, people actually believed they had found gold – it was dug up and blasted until the finds turned out to be worthless „cat’s gold“.
This gave rise to the world of the Rauschbergmandl: small, dwarf-like creatures that live in the mountains. The real route becomes an invisible choreography – the curves of the Fly-Line Ruhpolding are artistically integrated into the scenes.
Visible from the outside: The guests extend their arms towards the virtual gold pieces.
A journey turns into a little game
The race is not a passive VR ride. Even children understand the task without explanation – and for adults, the scoring system creates a playful, competitive moment: Who has collected the most gold?
Collecting gold with your hands
During the journey, gold pieces appear that are collected by hand interaction. At the end, they are counted.
The valley station as a mixed reality finale
A virtual bear appears in the real station and presents the results of the gold search – instead of a menu or a loading screen.
The mountain journey as the second chapter
Illustratively, sometimes comical: inspired by historical postcards and motifs from Ruhpolding, such as the church. What you see down there is what you hear up there.
A system for daily public operations
A functioning demonstration is at Location-based XR Not yet a finished product. The VR experience at Fly-Line Ruhpolding runs on seven Pico headsets – managed via a specially developed administration solution for the local staff.
Manage devices
Start headsets and monitor their status.
Reproducible
The application starts reliably the same every time you start driving.
Low maintenance
The administration solution supports the on-site team in managing and launching the headsets. After setup and training, regular operations can be carried out without ongoing technical support from developers.
The technology is complex – the experience itself is meant to be of course feel.
For the Fly-Line Ruhpolding, one of the most technically demanding projects by design4real, there was no standard solution. The guest noticed very little of it: he put on a pair of glasses, traversed caves, collected gold, returned to Mixed Reality, and experienced a story about Ruhpolding on the return journey.
Frequently asked questions about the project
Would you like to learn more about the technology behind the Fly-Line? Talk to us →
The Fly-Line Ruhpolding is a 500-meter-long ride through the forest on the Unternberg, in which guests glide down the mountain in a system suspended under the rails. design4real has developed a VR experience from this: During the real ride, the guests wear a VR headset and travel in sync with the movement through the cave world of the Rauschbergmandl.
Inside-out tracking is based on visual cues. In the forest, branches and leaves move, structures resemble one another, and light and shadow constantly change. The headset thus repeatedly lost its spatial positioning – the synchronization between reality and VR was lost.
With magnetic reference points along the route. A specially developed sensor on the moving system detects the magnets as they pass. The software checks each signal for plausibility – strength, duration, peak shape, section of travel, and expected sequence – and ignores interference from the steel structure.
The Experience runs on seven Pico headsets (Pico 4 Ultra Enterprise). The model allows for a deep understanding of the headset’s behavior, for example to specifically control tracking functions within the application. Additionally, there is the in-house magnetic sensor technology on the driving system.
On departure, take an interactive journey through the caves of Rauschbergmandl, where gold is collected by hand. At the valley station, a virtual bear presents the result in mixed reality. An immersive video tells the story on the mountain ride.
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