This post is part of a series of guides on how to write your first ACM SIGGRAPH / TOG paper. You can find the other articles here.
Some posts in this series cover a lot of technical detail. This one is less formal and more squishy, concentrating on stylistic issues for writing the introductory section of a technical paper.
In one sense the title, abstract, introduction, and entire paper, are increasingly longer versions of the same ideas. But they have different roles which should guide their construction. A good title is memorable and descriptive. The title and abstract are frequently read by someone who is deciding if they want to read your paper. If the answer will eventually turn out to be no, you will help them make better use of their time—allowing them to make an early exit—by being specific and concrete in your abstract and introduction.
An introduction is most useful when it helps align the reader’s expectation with your perspective of the paper’s content. Often a title will catch my attention, then I find the abstract a bit confusing, and I am well into the body of the paper before I realize that I misunderstood something about the paper’s scope. Perhaps unfamiliar terminology caused some ambiguity. Or the author’s assumptions and perspective were not made sufficiently clear. If a reader has not correctly understood the context, the body of the paper may feel confusing.
This is unfortunate when the reader is another scholar seeking to understand your work. It is even worse when the confused/frustrated reader is a reviewer deciding whether your draft paper will be accepted for publication. As an author you should work hard to ensure the typical reader can easily understand your exposition. This effort will be rewarded by helping a reviewer see the value of your contribution.
At a minimum, an introduction should provide needed background. Initially assume your reader knows nothing about your specific topic. In a few sentences, explain the topic in simple concise language that could be easily understood by almost anyone. Then in a bit more detail, describe the specific topic of your paper. Explain what is unknown or unsolved, and how your research seeks to fill that gap. The introduction should function like a funnel, leading readers with various backgrounds and perspectives to become aligned with your view of the topic and your approach to solving an aspect of it. This helps them assimilate what follows.
Experts in your field probably know what you are talking about, the introduction is a chance to catch the attention of non-experts, or experts from other fields, who may be surprised to learn they are interested in your research. For those readers, your paper could be the first time they have even thought about this topic. Craft your introduction to lead these readers to a basic understanding.
If your topic has been well trod by other researchers, be sure to explain how your approach is unique, or perhaps how it works better than others. It might help to imagine a potential reader who has just read two other papers on this topic, and is trying to decide if yours is worthwhile. Can you convince them to read on?
Order of writing: some authors find it easiest to start in the middle of your paper, with the technical aspects on which you have been focused for so long. Once the middle has been drafted, the introduction can be written to provide a smooth “on ramp” into the gist of the paper. In this approach the abstract is written last, after the introduction.
Bear in mind that you have been focused on your paper’s topic for months, if not years. You are not a good judge of what is obvious and what will be a confusing stumbling block to a reader coming in cold. It can be useful to have others read your introductory materials (title, abstract, introduction). Others in your research group may have useful feedback but in a sense they “know too much.” It is especially helpful to recruit people with significantly different backgrounds. People from other labs perhaps, or better, people from other departments. Can that friend of a friend over in biochemistry (or political science, or history) make any sense out of your introduction? Significant others or family members may help spot missing steps you forgot to mention because they are “obvious.”
If you can get someone with a differing background (perhaps wildly differing) to try to read your introduction, take careful note of questions they ask. (“What does this word/acronym even mean?” “You use this phrase in a way that seems different from everyday usage.”) These are ideas you must express more clearly. Add a sentence to explain a problematic word. Explicitly point out how a phrase is used differently in the context of your work. If your relationship (with this non-colleague, non-technical) reader permits, perhaps ask them some simple, gentle questions about what they read. Did they manage to follow most, or any, of the points you tried to make?
If your paper is published, most who read it will be in a field close to yours, and so understand your terminology and perspective. On the other hand if you are lucky, your paper might have broad appeal and may attract scholars from other fields. Someone in your field, say your boss, or a reviewer, will not be put off by an extra sentence of explanation or clarification at the beginning of your paper. And it can be especially helpful to a reader with a different background.
While the abstract needs to be concisely worded, there is room in the introduction to make clear what is not in your paper. If your technique could be applied in 2d and 3d settings, the introduction should make explicit how it is used in your paper. Resist the temptation to be vague to make your technique seem more widely applicable (2d and 3d) if you only discuss one case.
If you wonder why you should put effort into helping others decide more quickly not to read your paper, flip it around. Say you are on deadline, deciding which of several papers to spend time reading. You would certainly appreciate a paper that avoids wasting your time by being clear up front what it is not about.
Any sort of abstractions, or simplifying assumptions, that are key to an initial understanding of your technique, should be called out in the introduction. You might have decided early in your research to make a simplifying assumption to make this first step toward a larger research goal. Be sure to explain this in the introduction: why the simplifying assumption is reasonable, and how it can inform the more general case. A danger here is that you may think of your work a being on the larger topic X, but forget to clarify that this paper is actually about “topic X, for the case where β=0.”
Some other articles about how to write a paper’s introduction. These are general guides from universities intended for students. There are also lots of commercial services providing proof reading and copy editing services. We are assuming you and your coauthors will do all the writing and editing for your paper:
- Journal Article: Introduction — CommKit, MIT Communication Lab
- Writing a Scientific Paper: Introduction — UCI Library
- Writing an Introduction for a Scientific Paper — U Wisconsin, WAC
Ideas about how to introduce your topic to a reader who is unfamiliar with it and help them understand why it is interesting:
- WIRED’s 5 LEVELS, videos where an expert “…Explains One Concept in 5 Levels of Difficulty.” These might help you think about how to demystify the topic—in which you are now an expert—so it can be more easily understood by others.
- Two Minute Papers by Károly Zsolnai-Fehér. While the videos have gotten longer over the years, his energetic and upbeat delivery will convince you the topic and this paper are fascinating.
Kevin Kelly wrote a list of 103 Bits of Advice I Wish I Had Known including: “Spend as much time crafting the subject line of an email as the message itself because the subject line is often the only thing people read.” A journal paper is not an email, and the ratio of time spent might be different, but crafting an effective introduction can significantly increase the audience for your paper.
Introduction used with permission from: Nielsen, Bojsen-Hansen, Stamatelos, Bridson. 2022. Physics-Based Combustion Simulation. ACM TOG 41, 5 (2022) https://doi.org/10.1145/3526213
Text from the introduction of [Nielsen 2022]
Role for introduction
Fire, from small-scale candle flames to enormous explosions, remains an area of special interest for visual effects in movies, games, and commercials.
Start with a basic concept: fire. Place in context of effects production.
The complex interaction between fluid dynamics, heat transfer, chemical reactions, flame propagation, and resulting illumination makes for highly complex visual phenomena, difficult for an artist to model procedurally or by hand.
Problem to be solved: difficult to “direct” simulated fire..
While digital simulation of combustion phenomena has come a long way in terms of realism, it still in many cases does not match the quality seen in practical special effects. The movie Backdraft is an example of the beautiful practical effects that can be achieved using a combination of real fuels such as liquid and gaseous propane, pressurized alcohol, diesel, and MAPP gas to create a wide range of flame effects including texture, richness, and color [Shay 1991].
Basis of comparison: practical effects.
So: this paper is about realistically simulating fire while making it easy to control.
The ultimate goal of our approach is to provide combustion simulation workflows which reduce the time required by the artist to achieve physically plausible results. Ideally, simulation results should be physically plausible by default in the sense that they should come close to matching real-world footage of practical effects if real-world input characteristics such as fuel, oxidizer, wind, and geometric colliders are specified accurately in the simulation.
Goal: realism through simulation of the physics of fire.
User-intensive control and proceduralism should ideally only be required for final artistic tweaks, hero shots, or when the combustion phenomenon behaves in a supernatural manner. Using existing tools, commercial and proprietary, based on previous research on combustion simulation for computer graphics, talented artists can produce both realistic and beautiful results. However, it does in many cases require great skill and a significant amount of tweaking time. Our overall philosophy is to expand the scope of the underlying mathematical modeling of combustion, seeking out what is visually critical, and to make well-documented approximations where a compromise of numerical accuracy in favor of computation speed and visual fidelity makes sense for computer graphics.
Realism by default, while allowing production artists to control the result when needed.
With this in mind, we needed to expand the scope of prior work on fire and combustion simulation in graphics. We here propose additional mathematical models of the thermodynamic properties and stoichiometry of many of the real-world fuels used in practical special effects such as propane—enabling, for example, the prediction of adiabatic flame temperatures, which again facilitates less tweaking in the rendering stage. We couple this to a model of heat transfer that includes convection, conduction, and radiation; our main contribution in heat transfer is to solve for radiative heating more accurately than prior graphics work, for example facilitating ignition at a distance without heating up the intervening air. We model the combustion as infinitely fast chemistry and couple this with the thin flame model [Nguyen et al. 2002] as well as explicit species diffusion. Furthermore, the laminar burning velocities are spatially varied based on local species and empirical measurements. The jump in normal velocity at the thin flame front is captured using a novel expression for the associated divergence and allows for a standard fixed-stencil geometric multigrid solver to be applied. We also include physically validated soot formation and oxidation, as well as water vapor production and condensation.
Explain how this work differs from previous approaches, and how its approach provides additional benefits.
Interestingly, several heuristic techniques have emerged in visual effects production that at closer inspection to some degree address shortcomings in the current state-of-the-art mathematical models used in graphics. One example is the use of post-processing techniques such as blurring and masking to fake radiative heating and cooling [Cioroba et al. 2018].
Previous improvements have an ad hoc quality which could be replaced by a more principled approach.
The combustion approach proposed in this article allows us to simulate a wide range of deflagration phenomena that can coexist in the same simulation. This includes a combination of premixed and diffusion flames based on real-world fuels and oxidizers not demonstrated in graphics before (Figure 1(a)), diffusion flames (Figure 1(b) and (c)), spatially varying flame propagation (Figure 1(d)), fireballs (Figures 1(e) and 14), soot formation in smoky flames (Figure 10), soot oxidation in non-smoking flames (Figure 11), water vapor condensation (Figure 13) and ignition at a distance (Figure 8).
Outline some specific benefits of this approach. Here by making reference to figures later in the paper.
More specifically, our contributions to the computer graphics community include […detailed list of technical contributions removed from here].
Our solver has been implemented as a plugin for Autodesk’s Bifrost and is currently in production use. All results have been rendered with Arnold.
Concreteness: identify well known commercial software to identify context.
A physics-based approach to fire simulation for computer graphics has also been advocated by for example Stam and Fiume , Melek and Keyser , Nguyen et al. , and Feldman et al. . In line with this research, the recent SCA 2020 keynote [Museth 2020] motivated a physics-based approach inspired by the problems faced in visual effects production when attempting to match real-world footage of an explosion using existing methods in computer graphics.
List previous physics-based fire simulation. Mention key criteria of matching live action scenes made with practical effects.
The work presented in this article includes material from and extends our SIGGRAPH 2019 talk on physics-based combustion simulation in Bifrost [Nielsen et al. 2019]. Our work is just one step on the way towards achieving the goal of physically plausible results by default. There are still many facets of turbulent combustion that computer graphics may benefit from and that could be explored. We also realize that the goal may be difficult to reach; in fact, turbulent combustion is not fully understood to this day [Peters 2000].
Connect with earlier versions of this work. Make clear this is not the last word in fire simulation.
This post is part of a series of guides on how to write your first ACM SIGGRAPH / TOG paper. You can find the other articles here.
We thank Yu Wang for proofreading.