Tunnel-in-the-Sky Displays

25 Feb 2020 by Christopher Noessel

“Tunnel in the Sky” is the name of a 1955 Robert Heinlein novel that has nothing to do with this post. It is also the title of the following illustration by Muscovite digital artist Vladimir Manyukhin, which also has nothing to do with this post, but is gorgeous and evocative, and included here solely for visual interest.

See more of Vladimir’s work here https://www.artstation.com/mvn78.

Instead, this post is about the piloting display of the same name, and written specifically to sci-fi interface designers.

Last week in reviewing the spinners in Blade Runner, I included mention and a passing critique of the tunnel-in-the-sky display that sits in front of the pilot. While publishing, I realized that I’d seen this a handful of other times in sci-fi, and so I decided to do more focused (read: Internet) research about it. Turns out it’s a real thing, and it’s been studied and refined a lot over the past 60 years, and there are some important details to getting one right.

Though I looked at a lot of sources for this article, I must give a shout-out to Max Mulder of TU Delft. (Hallo, TU Delft!) Mulder’s PhD thesis paper from 1999 on the subject is truly a marvel of research and analysis, and it pulls in one of my favorite nerd topics: Cybernetics. Throughout this post I rely heavily on his paper, and you could go down many worse rabbit holes than cybernetics. n.b., it is not about cyborgs. Per se. Thank you, Max.

I’m going to breeze through the history, issues, and elements from the perspective of sci-fi interfaces, and then return to the three examples in the survey. If you want to go really in depth on the topic (and encounter awesome words like “psychophysics” and “egomotion” in their natural habitat), Mulder’s paper is available online for free from researchgate.net: “Cybernetics of Tunnel-in-the-Sky Displays.”

What the heck is it?

A tunnel-in-the-sky display assists pilots, helping them know where their aircraft is in relation to an ideal flight path. It consists of a set of similar shapes projected out into 3D space, circumscribing the ideal path. The pilot monitors their aircraft’s trajectory through this tunnel, and makes course corrections as they fly to keep themselves near its center.

This example comes from Michael P. Snow, as part of his “Flight Display Integration” paper, also on researchgate.net.

Please note that throughout this post, I will spell out the lengthy phrase “tunnel-in-the-sky” because the acronym is pointlessly distracting.

Quick History

In 1973, Volkmar Wilckens was a research engineer and experimental test pilot for the German Research and Testing Institute for Aerospace (now called the German Aerospace Center). He was doing a lot of thinking about flight safety in all-weather conditions, and came up with an idea. In his paper “Improvements In Pilot/Aircraft-Integration by Advanced Contact Analog Displays,” he sort of says, “Hey, it’s hard to put all the information from all the instruments together in your head and use that to fly, especially when you’re stressed out and flying conditions are crap. What if we took that data and rolled it up into a single easy-to-use display?” Figure 6 is his comp of just such a system. It was tested thoroughly in simulators and shown to improve pilot performance by making the key information (attitude, flight-path and position) perceivable rather than readable. It also enabled the pilot greater agency, by not having them just follow rules after instrument readings, but empowering them to navigate multiple variables within parameters to stay on target.

In Wilckens’ Fig. 6, above, you can see the basics of what would wind up on sci-fi screens decades later: shapes repeated into 3D space ahead of the aircraft to give the pilot a sense of an ideal path through the air. Stay in the tunnel and keep the plane safe.

Mulder notes that the next landmark developments come from the work of Arthur Grunwald & S. J. Merhav between 1976–1978. Their research illustrates the importance of augmenting the display and of including a preview of the aircraft in the display. They called this preview the Flight Path Predictor, or FPS. I’ve also seen it called the birdie in more modern papers, which is a lot more charming. It’s that plus symbol in the Grunwald illustration, below. Later in 1984, Grunwald also showed that a heads-up-display increased precision adhering to a curved path. So, HUDs good.

n.b. This is Mulder’s representation of Grunwald’s display format.

I have also seen lots of examples of—but cannot find the research provenance for—tools for helping the pilot stay centered, such as a “ghost” reticle at the center of each frame, or alternately brackets around the FPP, called the Flight Director Box, that the pilot can align to the corners of the frames. (I’ll just reference the brackets. Gestalt be damned!) The value of the birdie combined with the brackets seems very great, so though I can’t cite their inventor, and it wasn’t in Mulder’s thesis, I’ll include them as canon.

The takeaway from the history is really that these displays have a rich and studied history. The pattern has a high confidence.

Elements of an archetypical tunnel-in-the-sky display

There are lots of nuances that have been studied for these displays. Take for example the effect that angling the frames have on pilot banking, and the perfect time offset to nudge pilot behavior closer to ideal banking. For the purposes of sci-fi interfaces, however, we can reduce the critical components of the real world pattern down to four.

Square shapes (called frames) extending into the distance that describe an ideal path through space
1. The frame should be about five times the width of the craft. (The birdie you see below is not proportional and I don’t think it’s standard that they are.)
2. The distances between frames will change with speed, but be set such that the pilot encounters a new one every three seconds.
3. The frames should adopt perspective as if they were in the world, being perpendicular to the flight path. They should not face the display.
4. The frames should tilt, or bank, on curves.
5. The tunnel only needs to extend so far, about 20 seconds ahead in the flight path. This makes for about 6 frames visible at a time.
An aircraft reference symbol or Flight Path Predictor Symbol (FPS, or “birdie”) that predicts where the plane will be when it meets the position of the nearest frame. It can appear off-facing in relation to the cockpit.
1. These are often rendered as two L shapes turned base-to-base with some space between them. (See one such symbol in the Snow example above.)
2. Sometimes (and more intuitively, imho) as a circle with short lines extending out the sides and the top. Like a cartoon butt of a plane. (See below.)
Contour lines connect matching corners across frames
A horizon line

This comp illustrates those critical features.

There are of course lots of other bits of information that a pilot needs. Altitude and speed, for example. If you’re feeling ambitious, and want more than those four, there are other details directly related to steering that may help a pilot.

Degree-of-vertical-deviation indicator at a side edge
Degree-of-horizontal-deviation indicator at the top edge
Center-of-frame indicator, such as a reticle, appearing in the upcoming frame
A path predictor
Some sense of objects in the environment: If the display is a heads-up display, this can be a live view. If it is a separate screen, some stylized representation what the pilot would see if the display was superimposed onto their view.
What the risk is when off path: Just fuel? Passenger comfort? This is most important if that risk is imminent (collision with another craft, mountain) but then we’re starting to get agentive and I said we wouldn’t go there, so *crumbles up paper, tosses it*.

I haven’t seen a study showing efficacy of color and shading and line scale to provide additional cues, but look closely at that comp and you’ll see…

The background has been level-adjusted to increase contrast with the heads-up display
A dark outline around the white birdie and brackets to help visually distinguish them from the green lines and the clouds
A shadow under the birdie and brackets onto the frames and contours as an additional signal of 3D position
Contour lines diminishing in size as they extend into the distance, adding an additional perspective cue and limiting the amount of contour to the 20 second extents.

What can you play with when designing one in sci-fi?

Everything, of course. Signaling future-ness means extending known patterns, and sci-fi doesn’t answer to usability. Extend for story, extend for spectacle, extend for overwhelmedness. You know your job better than me. But if you want to keep a foot in believability, you should understand the point of each thing as you modify it and try not to lose that.

Each frame serves as a mini-game, challenging the pilot to meet its center. Once that frame passes, that game is done and the next one is the new goal. Frames describe the near term. Having corners to the frame shape helps convey banking better. Circles would hide banking.
Contour lines, if well designed, help describe the overall path and disambiguate the stack of frames. (As does lighting and shading and careful visual design, see above.) Contour lines convey the shape of the overall path and help guide steering between frames. Kind of like how you’d need to see the whole curve before drifitng your car through one, the contour lines help the pilot plan for the near future.
The birdie and brackets are what a pilot uses to know how close to the center they are. The birdie needs a center point. The brackets need to match the corners of the frame. Without these, it’s easier to drift off center.
A horizon line provides feedback for when the plane is banked.

THIS BAD: You can kill the *sense* of the display by altering (or in this case, omitting) too much.

Since I mentioned that each frame acts as a mini-game, a word of caution: Just as you should be skeptical when looking to sci-fi, you should be skeptical when looking to games for their interfaces. The simulator which is most known for accuracy (Microsoft Flight Simulator) doesn’t appear to have a tunnel-in-the-sky display, and other categories of games may not be optimizing for usability as much as just plain fun, with the risk of crashing your virtual craft just being part of the risk. That’s not an acceptable outcome in real-world piloting. So, be cautious considering game interfaces as models for this, either.

This clip of stall-testing in the forthcoming MSFS2020 still doesn’t appear to show one.

So now let’s look at the three examples of sci-fi tunnel-in-the-sky displays in chronological order of release, and see how they fare.

Three examples from sci-fi

So with those ideal components in mind, let’s look back at those three examples in the survey.

Quick aside on the Blade Runner interface: The spike at the top and the bottom of the frame help in straight tunnels to serve as a horizontal degree-of-deviation indicator. It would not help as much in curved tunnels, and is missing a matching vertical degree-of-deviation indicator. Unless that’s handled automatically, like a car on a road, its absence is notable.

*Starship Troopers* (1986) We only get 15 frames of this interface in *Starship Troopers*, as Ibanez pilots the escape shuttle to the surface of Planet P. It is *very* jarring to see as a repeating gif, so accept this still image instead.

Some obvious things we see missing from all of them are the birdie, the box, and the contour lines. Why is this? My guess is that the computational power in the 1976 was not enough to manage those extra lines, and Ridley Scott just went with the frames. Then, once the trope had been established in a blockbuster, designers just kept repeating the trope rather than looking to see how it worked in the real world, or having the time to work through the interaction logic. So let me say:

Without the birdie and box, the pilot has far too much leeway to make mistakes. And in sci-fi contexts, where the tunnel-in-the-sky display is shown mostly during critical ship maneuvers, their absence is glaring.
Also the lack of contour lines might not seem as important, since the screens typically aren’t shown for very long, but when they twist in crazy ways they should help signal the difficulty of the task ahead of the pilot very quickly.

Note that sci-fi will almost certainly encounter problems that real-world researchers will not have needed to consider, and so there’s plenty of room for imagination and additional design. Imagine helping a pilot…

Navigating the weird spacetime around a singularity
Bouncing close to a supernova while in hyperspace
Dodging chunks of spaceship, the bodies of your fallen comrades, and rising plasma bombs as you pilot shuttlecraft to safety on the planet below
AI on the ships that can predict complex flight paths and even modify them in real time, and even assist with it all
Needing to have the tunnel be occluded by objects visible in a heads up display, such as when a pilot is maneuvering amongst an impossibly-dense asteroid field.

…to name a few off my head. These things don’t happen in the real world, so would be novel design challenges for the sci-fi interface designer.

So, now we have a deeper basis for discussing, critiquing, and designing sci-fi tunnel-in-the-sky displays. If you are an aeronautic engineer, and have some more detail, let me hear it! I’d love for this to be a good general reference for sci-fi interface designers.

If you are a fan, and can provide other examples in the comments, it would be great to see other ones to compare.

Happy flying, and see you back in Blade Runner in the next post.

Spinners (flying cars)

21 Feb 2020 by Christopher Noessel

So the first Fritzes are now a thing. Before I went off on that awesome tangent, where were we? Oh that’s right. I was reviewing Blade Runner as part of a series on AI in sci-fi. I was just about to get to Spinners. Now vehicles are complicated things as they are, much less when they are navigating proper 3D space. Additionally, the police force is, ostensibly, a public service, which complicates things even further. So this will get lengthy. Still, I think I can get this down to eight or so subtopics.

In the distant future of 2019⸮, flying cars, called “spinners,” are a reality. They’re largely for the wealthy and powerful (including law enforcement). The main protagonist, Deckard, is only ever a passenger in a few over the course of the film. His partner Gaff flies one, though, so we have enough usage to review.

Opening the skies to automobile-like traffic poses challenges, especially when those skies are as full of lightning bolts, ever-present massive flares, distracting building-sized video advertisements, and of course, other spinners.

Piloting controls

To pilot the spinner, Gaff keeps his hands on each handle of a split yoke. Within easy reach of his fingers are a few unlabeled buttons and small lights. Once we see him reach with his right thumb to press one of the buttons, but we don’t see any result, so it’s not clear what these buttons do. It’s nice that they don’t require him to take his hands off the controls. (This might seem like a prescient concept, but WP tells me the first non-horn wheel-mounted controls date back as far back as 1966.)

It is contextualizing to note the mode of agency here. That is, the controls are manual, with no AI offering assistance or acting as an agent. (The AI is in the passenger’s seat, lol fight me.) It appears to be up to Gaff to observe conditions, monitor displays, perform wayfinding, and keep the spinner on track.

Note that we never see what his feet are doing and never see him doing other things with his hands other than putting on a headset before lift-off. There are lots of other controls to the pilot’s left and in the console between seats, but we never see them in use. So, you know, approach with caution. There are a lot of unknowns here.

The Traditional Chinese characters on the window read “No entry,” for citizens outside the spinner, passing by when it is on the ground. (Hat tips for the translation to Mischa Park-Doob and Frank Chung.)

The spinner is more like a VTOL aircraft or helicopter than a spaceship. That is, it is constantly in the presence of planetary gravity and must overcome the constant resistance of air. So the standards I established in the piloting controls post are of only limited use to us here.

So let’s look at how helicopter controls work. The FAA Helicopter Flying Handbook tells us that a pilot has controls for…

The vertical velocity, up or down. (Controlled by the angle of the control stick called the collective. The collective is to the left of the pilot’s hip when they are seated.)
The thrust. (Controlled by the twistgrip on the collective.)
Movement forward, rearward, left, and right. (Controlled with the stick in front of the pilot, called the cyclic.)
Yaw of the vehicle. (Controlled with the pair of antitorque pedals at the pilot’s feet.)

Since we don’t see Gaff when the spinner is moving up and down, let’s presume that the thing he’s gripping is like a Y-shaped cyclic, with lots of little additional controls around the handles. Then, if we presume he has a collective somewhere out of sight to his left and antitorque pedals at his feet, this interface meets modern helicopter standards for control. From the outside, those appear to be well mapped (collective up = helicopter up, cyclic right = helicopter right). Twist for thrust is a little weird, but it’s a standard and certainly learnable, as I recall from my motorcycling days. So let’s say it’s complete and convincing. Is it the best it could be? I’m not enough of an aeronautical engineer (read: not at all) to imagine better options, so let’s move along. I might have more to say if it was agentive.

Dashboard

There are two large screens in the dashboard. The one directly in front of Gaff shows a stylized depiction of the 3D surfaces around him as cyan highlights on a navy blue background. Approaching red shapes describe a pill-shaped tunnel-in-the-sky display. These have been tested since 1981 and found to provide higher tracking performance to ideal paths in manual flight, lower cognitive workload, and enhanced situational awareness. (https://arc.aiaa.org/doi/abs/10.2514/3.56119) So, this is believable and well done. I’m not sure that Gaff could readily use the 3D background to effectively understand the 3D terrain, but it is tertiary, after the real world and the tunnel display.

I have to say that it’s a frustrating anti-trope to run into again, but it must be said: If the spinner knows where the ship should be, and general artificial intelligence exists in this diegesis, why exactly are humans doing the piloting? Shouldn’t the spinner fly itself? But back to the interfaces…

Above the tunnel-in-the-sky display is a cyan 7-segment LED scroll display. In the gif above it displays “MAXIMUM SPEED” and later it provides some wayfinding text. I’m not sure how many different types of information it is meant to cycle through, but it sure would be a pain to wait for vital information to appear, and distracting to have to control it to get to the one you wanted.

There is also a vertical screen in the middle of the console listing cyan labels ALT, VEL, and PTCH. These match to altitude, velocity, and pitch variables, reinforcing the helicopter model. The yellow numbers below these labels change in the scene very slowly, and—remarkably for a four-second interface from 1982—do not appear to change randomly. That’s awesome.

But then, there’s a paragraph of cyan text in the middle of the screen that appears over the course of the scene, letter by letter. This animation calls unnecessary attention to itself. There are also smaller, thin screens in the pilot’s door that also continually scroll that same teeny tiny cyan text. I’m not sure WTF all this text is supposed to be, since it would be horribly distracting to a pilot. There are also a few rows of white LEDs with cylon-eye displays traveling back and forth. They are distracting, but at least they’re regular, and might be habituate-able and act as some sort of ambient display. Anyway, if we were building this thing for real, we’d want to eliminate these.

Lastly, at the bottom of the center screen are some unlabeled bar charts depicting some variables that appear to be wiggling randomly. So, like, only the top fifth of this screen can be lauded. The rest is fuigetry. *sigh* It’s hard to escape.

Wayfinding

To help navigate the 3D space, pilots have a number of tools. First, there are windows where you expect windows to be in a car, and there are also glass panels under their feet. The movie doesn’t make a big deal out of it, but it’s clear in the scene where the spinner lifts off from the street level. These transparent panes surround pilots and passengers and allow them to track visual cues for landmarks and to identify collision threats.

It’s reflecting some neon on the street below.

The tunnel-in-the-sky display above is the most obvious wayfinding tool. Somehow Gaff has entered a destination, and the tunnel guides him where it needs to go. Since this entails a safe path through the air, it’s the most important display. Other bits of information (like the ALT, VEL, and PTCH in the center screen) should be oriented around it. This would make them glanceable, allowing Gaff glance to check them and quickly return his eyes to the windshield. In fact, we have to admit that a heads up display would allow Gaff to keep his attention where it needs to be rather than splitting it between the real world and these dashboard displays. Modern vehicle drivers are used to this split attention, and can manage it well enough. But I suspect that a HUD would be better.

It’s also at this point that you begin to wonder if these are the scout ships we see in *Close Encounters*.

There is also that crawling LED display above the tunnel-in-the-sky screen. In one scene it shows “SECTOR FOUR (4)…QUAD-” (we don’t get to see the end of this phrase) but it implies that one of the bits of information this scroll provides is a reminder of the name of the neighborhood you’re currently in. That really only helps if you’re way off course, and seems too low a fidelity for actual wayfinding assistance, but presuming the tunnel-in-the-sky is helping provide the rest of the wayfinding, this information is of secondary importance.

A special note about takeoff: ENVIRON CTR

The display sequence infamous for appearing in both Alien and Blade Runner happens as Gaff lifts off in a spinner early in the film. White all-cap letters label this blue screen “ENVIRON CTR,” above a grid of square characters. Then two 8-digit sequences “drop” down the center of the square grid: 92886599 | 95654085. Once they drop 3 rows, the background turns red, the grid disappears to be replaced by a big blinking label PURGE. Characters at the bottom read “24556 DR 5”, and don’t change.

After the spinner lifts off the display shows a complex diagram of a circle-within-a-circle, illustrating the increasing elevation from the ground below. The delightful worldbuilding thing about the sequence is that it is inscrutable, and legible only by a trained driver, yet gets full focus on screen. There’s not really enough information about the speculative engineering or functional constraints of the spinner to say why these screens would be necessary or useful. I have a suspicion that a live camera view would be more useful than the circle-within-a-circle view, but gosh, it sure is cool. Here’s the shot from Alien, by the way, for easy comparison.

Since people seem to be all over this one now, let me also interject that Alien is also connected to Firefly, since Mal’s anti-aircraft HUD in the pilot had a Weyland-Yutani logo. Chew on that trivia, Internet.

Intercar communication

Of special note is a scene just before his call to Sebastian’s apartment. Deckard is sitting in his parked vehicle in a call with Bryant. A police spinner glides by and we hear an announcement over his loudspeaker, directed to Deckard’s vehicle saying, “This sector’s closed to ground traffic. What are you doing here?” From inside his vehicle, Deckard looks towards his video phone in the console (we never see if there is video, but he’s looking in that direction rather than out the window) and without touching a thing, responds defensively, “I’m working. What are you doing?” The policeman’s reply comes through the videophone’s speakers, “Arresting you, that’s what I’m doing.”

Note that Deckard did not have to answer the call or even put Bryant on hold. We don’t know what the police officer did on their end, but this interaction implies that the police can make an instant, intrusive audio connection with vehicles it finds suspicious. It’s so seamless it will slip by you if you don’t know to look for it, but it paints quite a picture of intercar communication. Can you imagine if our cars automatically shared an audio space with the cars around it?

External interfaces

Another aspect of the car is that it is an interface not just for the people using the car, but for the citizens observing or near the spinner as it goes about its business. There are a number of features that helps it act as an interface to the public.

Police exist as a social service, and the 995 repeated around the outside helps remind citizens of the number they can call in case of an emergency.

Modern patrol cars have beacons and sirens to tell other drivers to get out of the way when they are on urgent business. Police spinners are gravid with beacons, having 12 of them visible from the front alone. (See below.) As the spinner is taking off, yellow and blue beacons circle as a warning. This would be of no help to a blind person nearby, but the vehicle does make some incidental noise that serves as an audible warning.

The rich light strip makes sense because it has such a greater range of movement than ground-based cars, and needs more attention grabbing power. Another nice touch is that, since the spinner can be above people, there are also beacons on the chassis.

Upshot: Spinners do well

So, all in all, the spinner fares quite well on close inspection. It builds on known models of piloting, shows mostly-relevant data, uses known best practices for assistance, and has a lot of well-considered surface features for citizens.

Now if only I could figure out why they’re called spinners.

Escape pod and insertion windows

11 Dec 2014 by Christopher Noessel

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When the Rodger Young is destroyed by fire from the Plasma Bugs on Planet P, Ibanez and Barcalow luckily find a functional escape pod and jettison. Though this pod’s interface stays off camera for almost the whole scene, the pod is knocked and buffeted by collisions in the debris cloud outside the ship, and in one jolt we see the interface for a fraction of a second. If it looks familiar, it is not from anything in Starship Troopers.

vlcsnap-2014-12-09-21h16m18s69
The interface features a red wireframe image of the planet below, outlined by a screen-green outline, oriented to match the planet’s appearance out the viewport. Overlaid on this is a set of screen-green rectangles, twisting as they extend in space (and time) towards the planet. These convey the ideal path for the ship to take as it approaches the planet.

I’ve looked through all the screen grabs I’ve made for this movie, and there no other twisting-rectangle interfaces that I can find. (There’s this, but it’s a status-indicator.) It does, however, bear an uncanny resemblance to an interface from a different movie made 18 years earlier: Alien. Compare the shot above to the shot below, which is the interface Ash uses to pilot the dropship from the Nostromo to LV-426.

Alien-071

It’s certainly not the same interface, the most obvious aspect of which is the blue chrome and data, absent from Ibanez’ screen. But the wireframe planet and twisting rectangles of Starship Troopers are so reminiscent of Alien that it must be at least an homage.

Planet P, we have a problem

Whether homage, theft, or coincidence, each of these has a problem as far as the interaction design. The rectangles certainly show the pilot an ideal path in a way that can instantly be understood even by us non-pilots. At a glance we understand that Ibanez should roll her pod to the right. Ash will need to roll his to the left. But how are they actually doing against this ideal? How is the pilot doing compared to that goal at the moment? How is she trending? It’s as if they were driving a car and being told “stay in the center of the middle lane” without being told how close to either edge they were actually driving.

Rectangle to rectangle?

The system could use the current alignment of the frame of the screen itself to the foremost rectangle in the graphic, but I don’t think that’s what happening. The rectangles don’t match the ratio of the frame. Additionally, the foremost rectangle is not given any highlight to draw the pilot’s attention to it as the next task, which you’d expect. Finally that’s a level of abstraction that wouldn’t fit the narrative as well, to immediately convey the purpose of the interface.

Show me me

Ash may see some of that comparison-to-ideal information in blue, but the edge of the screen is the wrong place for it. His attention would be split amongst three loci of attention: the viewport, the graphic display, and the text display. That’s too many. You want users to see information first, and read it secondarily if they need more detail. If we wanted a single locus of attention, you could put ideal, current state, and trends all as a a heads-up display augmenting the viewport (as I recommended for the Rodger Young earlier).

If that broke the diegesis too much, you can at least add to the screen interface an avatar of the ship, in a third-person overhead view. That would give the pilot an immediate sense of where their ship currently is in relation to the ideal. A projection line could show the way the ship is trending in the future, highlighting whether things are on a good or not so good path. Numerical details could augment these overlays.

By showing the pilot themselves in the interface—like the common 3rd person view in modern racing video games—pilots would not just have the ideal path described, but the information they need to keep their vessels on track.

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