Guidelines for Drawing Immersive Panoramas in Equirectangular Perspective
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Guidelines for Drawing Immersive Panoramas in Equirectangular Perspective António Araújo Universidade Aberta (UAb) R. da Escola Politécnica, 141-147 Lisbon, Portugal 1269-001 Centro de Matemática, Aplicações Fundamentais e Investigação Operacional (CMAF-CIO) Faculdade de Ciências da Universidade de Lisboa Lisbon, Portugal Research Centre for Arts and Communication, Universidade Aberta (CIAC-UAb) Lisbon, Portugal [email protected] ABSTRACT 1 INTRODUCTION Virtual Reality (VR) Panoramas work by interactively creating im- Virtual Reality panoramas are increasingly popular in social media. mersive anamorphoses from spherical perspectives. These pano- Facebook, Google, and Flickr all provide relatively easy ways for ramas are usually photographic but a growing number of artists the user to upload his own 360 degree photographic panoramas and are making hand-drawn equirectangular perspectives in order to share them as VR experiences, as long as he has the right equipment. visualize them as VR panoramas. This is a practice with both artistic The image is uploaded as an equirectangular perspective picture and didactic interest. However, these drawings are usually done by and the platform’s rendering software provides the VR experience, trial-and-error, with ad-hoc measurements and interpolation of pre- by monitoring the direction of view of the user’s mobile phone computed grids, a process with considerable limitations. We develop or headset and displaying at each instant a plane perspective - in in this work the analytic tools for plotting great circles, straight fact a conical anamorphosis - of a certain FOV from within the line images and their vanishing points, and then provide guidelines total picture. Although these panorama viewers were intended as for achieving these constructions in good approximation without a photographic display, some artists have chosen to subvert them computer calculations, through descriptive geometry diagrams that to display drawn panoramas instead. The drawing is accepted by can be executed using only ruler, compass, and protractor. the VR rendering software after injection of the adequate EXIF information into the picture’s file, which makes it pass for a photo CCS CONCEPTS from a supported 360-degree camera. There is an interesting col- • Applied computing → Fine arts; Media arts; Computer-assisted lection of these drawings at Flickr’s artistic panorama group [8]. instruction; Interactive learning environments; Architecture (buil- See also the whimsical examples by David Anderson [2] and the dings); virtuoso on-location drawings by Gerard Michél [11, 12]. This inte- rest in drawing VR panoramas seems part of a trend. Illustrators KEYWORDS and urban sketchers (the present author being a member of both tribes) seem recently more interested in both curvilinear perspecti- immersive art, immersive panoramas, VR panoramas, equirectan- ves and anamorphoses. Such waves of enthusiasm seem to arise gular perspective, spherical perspective, perspective, drawing, des- with every time anamorphosis finds a new technological expression. criptive geometry, digital art, ruler and compass, social networks The current VR experience rehashes that of the now forgotten but ACM Reference format: once extremely popular 19th century panoramas for the display António Araújo. 2017. Guidelines for Drawing Immersive Panoramas in of which large rotundas were built [9], and, before that, the im- Equirectangular Perspective. In Proceedings of ARTECH2017, Macau, China, mersive spectacle of illusionary Church ceilings. These large scale September 06-08, 2017, 7 pages. immersive anamorphoses were drawn out in plan and elevation https://doi.org/10.1145/3106548.3106606 as if to build real architecture (and sometimes in replacement of such, as in the case of Andrea Pozzo’s famous dome [10]), and then were painted as an optical illusion - a visual simulacrum - of Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed the imagined object. Drawn VR panoramas provide an analogous for profit or commercial advantage and that copies bear this notice and the full citation experience, in a smaller, less expensive scale. Here too the artist on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or starts with a flat perspective drawing and aims at an immersive republish, to post on servers or to redistribute to lists, requires prior specific permission experience. The difference is that, unlike the firmly grounded clas- and/or a fee. Request permissions from [email protected]. sical perspective work of Pozzos treatise [14], most equirectangular ARTECH2017, September 06-08, 2017, Macau, China drawings are made by using precomputed grids, by sheer trial and © 2017 Copyright held by the owner/author(s). Publication rights licensed to Associa- tion for Computing Machinery. error, or by merely drawing on top of photographs. There seems ACM ISBN 978-1-4503-5273-4/17/09...$15.00 to be no comprehensive description available of the properties and https://doi.org/10.1145/3106548.3106606 ARTECH2017, September 06-08, 2017, Macau, China António Araújo constructions of equirectangular perspective that is adequate for perspective drawing. This specific type of visualization will in turn a human draughtsman rather than a computer that can just brute feed back into the drawing process, nor merely as a verification force its way through any rendering. Artist’s are notorious hackers tool but as a motivator of specific aesthetics (the VR display isa of ad-hoc perspective, classical or otherwise, but this lack is more reading mode and there is no such thing as a passive reading mode) serious for educational applications. Anamorphosis is a good vehi- and therefore of the need to solve geometric problems that derive cle for teaching descriptive geometry to young students [4]. They from these aesthetic goals. motivate the student by allowing him to build a real, impressive But if the VR panorama is to have such didactic applications, a object that he can share with his friends and whose construction clear method is required to plot the perspectives by hand, not only both requires and facilitates the learning of descriptive geometry. within precomputed grids (which are just another limiting black VR panoramas integrate well with this approach since they enable box), but for all general line projections. That is, one must solve the the sharing in social networks not only of the static photograph of perspective. This is what I propose here, in two parts: First I develop the resulting anamorphosis, but the actual immersive experience of the analytic and computational tools for the systematic plotting of the imagined object’s visual presence. Yet there is more to this than great circles, straight line images and their vanishing points. Next, I mere motivational value. It can be argued that technology tends provide diagrammatic methods to achieve these constructions wit- to generate a paradoxical type of ignorance regarding the very hout a computer, so as to draw general equirectangular projections, principles that it streamlines [17], and that this is true in particular from observation or orthographic plans, using only ruler, compass, of the naive use of digital tools in art [15]. That you can click a and protractor. menu and get a perspective picture might be expected to enhance your knowledge of perspective, but instead hinders it, first by ex- pressing it in terms of the machine’s primitive operations rather than the human’s (brute force pixel-by-pixel plots rather than ruler and compass operations) and then by black boxing the process out 2 SOLVING EQUIRECTANGULAR of view through abstraction and encapsulation, which itself limits PERSPECTIVE one’s modes of thought and expression [13]; instead of learning A central perspective can be defined as a conical projection (ana- perspective one learns to turn the knobs on an opaque box whose morphosis) onto a surface, followed by a flattening map that maps interface, of a stranger’s design, defines the scope of one’s possible the surface onto a plane. These include cylindrical perspective, action and thought. There is a mode of knowledge of space and (hemi-)spherical perspective, and several flavours of total spherical form that you only get from drawing with your hands and compu- perspective. ting with your brain. The digital artist profits from making drawing In the spherical case, the anamorphosis is simply the map P 7! a part of his flow even if drawing is not his goal. That he cangeta OP/jOP j where O is the center of the sphere, representing the obser- perspective at the click of a button only makes it more urgent that ver’s viewpoint. The flattenings are usually mappings well known he knows how to get one through his mind and hands. The machine from cartography. What is usually just called spherical perspective should help us know rather than trapping us by making knowing is anamorphosis onto a sphere followed by the azimuthal equidis- seem unnecessary. As a foil to this trap, the present author has tant projection. The good thing about this projection is that lines argued [5] for a “deliberate rudimentarization” or “cardboarding” in are turned into approximate arcs of circle in the frontal hemisphere teaching the concepts behind digital tools - exposing the conceptual ([1], [7]) or, in the general case, into curves that can be obtained gears of digital black boxes by reducing them to their most basic from these arcs by elementary means [3]. This facilitates solving physical expression. The aim is to translate between the human by ruler and compass. and the machine-executable, creating feedback loops between the Equirectangular projections of lines are clearly not as simple as two so as to enhance the understanding of both, and create locci arcs of circle, as can be seen in a comparison of the two projections for meaningful artistic intervention upon the tools themselves.