Basic Scene Generation for Night Sky

Journal of Skyscape Archaeology

For centuries, the rich nocturnal environment of the starry sky could be modelled only by analogue tools such as paper planispheres, atlases, globes and numerical tables. The immersive sky simulator of the twentieth century, the optomechanical planetarium, provided new ways for representing and teaching about the sky, but the high construction and running costs meant that they have not become common. However, in recent decades, “desktop planetarium programs” running on personal computers have gained wide attention. Modern incarnations are immensely versatile tools, mostly targeted towards the community of amateur astronomers and for knowledge transfer in transdisciplinary research. Cultural astronomers also value the possibilities they give of simulating the skies of past times or other cultures. With this paper, we provide an extended presentation of the open-source project Stellarium, which in the last few years has been enriched with capabilities for cultural astronomy research n...

ijser.org

In the rendering of outdoor scenes in virtual environments, the sun's position, sky color, clouds, shadow, trees, grass etc play very important roles in making it realistic. In this paper Sky color and the sun's position are combined. Specific longitude, latitude, date and time are required parameters to calculate the exact position of the sun. The sun's position is calculated based on Julian dating; the sky's color is created by Perez modeling. A functional application is designed to show the position of the sun and then sky color in arbitrary location, date and time. It can be possible to use this application in commercial games for outdoor rendering and for teachers to teach some part of physics about earth orbit and effect of the sun on the sky and it can be used in building design.

2009

Modeling illumination of outdoor objects by natural light sources - the Sun, the Moon and the stars - is a very difficult problem due to highly complex physics of light rays and the Earth's atmosphere. Although there are many studies in the literature on modeling of astronomic and atmospheric phenomena, of emission, scattering and absorption of light rays through the atmosphere, and of the illumination of surfaces; it is very difficult to reach these algorithms, equations and their parameter values readily available in a single source. In this paper, we present an approach that collects available methodologies in the literature into one consistent model for direct (non-scattered) illumination during daytime and at night, which is a part of an ongoing project that started in November 2002.

2006

The objective of this paper is to establish the VSD as a generic method to set up daylight for different light simulation software. The validation against measured data is published in a prior paper (Wittkopf., 2005). A Virtual Sky Dome (VSD) is a hemisphere comprising of 145 light sources with distinct intensity that resemble the sky luminance distribution for any location, time and sky type. The light properties are calculated by a spreadsheet tool and used to write scene files for the software Lightscape, Radiance and Photopia. Eventually diffuse illuminance under a selected sky type is compared, indicating that the VSD is a generic method to set up daylight.

CEIG, 2018

Figure 1: Effect of the location of the observer on the apperance of the atmosphere for different sun elevations. From left to right, URBAN and RURAL atmospheres with sun elevation at 0 • , DESERT and CLEAN MARITIME with sun elevation at 5 • , and URBAN and POLAR ARTIC with sun elevation at 25 •. All renders are set to January, and with the same atmosphere turbidity.

This paper presents a method to render synthetic sky images corresponding to given weather conditions. The method combines artificial neural networks and principal component analysis to associate the appearance of the sky with the state of a weather parameter vector. This association is then used to generate artificial sky images corresponding to a given weather parameter vector. The proposed method has important applications for example in flight simulators and in the game industry.

Proceedings of the 2005 ACM SIGCHI …, 2005

Monthly Notices of The Royal Astronomical Society, 2001

We present the first World Atlas of the zenith artificial night sky brightness at sea level. Based on radiance-calibrated high-resolution DMSP satellite data and on accurate modelling of light propagation in the atmosphere, it provides a nearly global picture of how mankind is proceeding to envelop itself in a luminous fog. Comparing the Atlas with the United States Department of Energy (DOE) population density data base, we determined the fraction of population who are living under a sky of given brightness. About two-thirds of the World population and 99 per cent of the population in the United States (excluding Alaska and Hawaii) and European Union live in areas where the night sky is above the threshold set for polluted status. Assuming average eye functionality, about one-fifth of the World population, more than two-thirds of the United States population and more than one half of the European Union population have already lost naked eye visibility of the Milky Way. Finally, about one-tenth of the World population, more than 40 per cent of the United States population and one sixth of the European Union population no longer view the heavens with the eye adapted to night vision, because of the sky brightness.

An overcast sky simulator, artificial sky, was originally developed in the fall of 2000 at the Faculty of Architecture and Fine Art at NTNU, Trondheim, Norway. During the design process the limits of the mirror box concept as an overcast sky simulator were investigated and the results were published in the Lighting Research and Technology in 2005. The ceiling of the artificial sky was made of evenly distributed fluorescent light tubes and a "perfectly" diffusing canvas stretched beneath. The development in LED-technology gives new possibilities regarding control of correlated colour temperature (CCT). The present development of the artificial sky consists of the construction of a new ceiling. It will be done by Spectro Color [1] using different types of LED-chips; additionally, a sophisticated solution for diffusion of light from LEDs was developed. The new ceiling will enable adjustment of the CCT from 2000K to 18000K in three illuminance levels: 100%, 50% and 25% of the ...

Night vision goggles (NVGs) are widely used by helicopter pilots for flight missions at night, but the equipment can present visually confusing images especially in urban areas. A simulation tool with realistic nighttime urban images would help pilots practice and train for flight with NVGs. However, there is a lack of tools for visualizing urban areas at night. This is mainly due to difficulties in gathering the light system data, placing the light systems at suitable locations, and rendering millions of lights with complex light intensity distributions (LID). Unlike daytime images, a city can have millions of light sources at night, including street lights, illuminated signs, and light shed from building interiors through windows. In this paper, a Procedural Lighting tool (PL), which predicts the positions and properties of street lights, is presented. The PL tool is used to accomplish three aims: (1) to generate vector data layers for geographic information systems (GIS) with statistically estimated information on lighting designs for streets, as well as the locations, orientations, and models for millions of streetlights; (2) to generate geo-referenced raster data to suitable for use as light maps that cover a large scale urban area so that the effect of millions of street light can be accurately rendered at real time, and (3) to extend existing 3D models by generating detailed light-maps that can be used as UV-mapped textures to render the model. An interactive graphical user interface (GUI) for configuring and previewing lights from a Light System Database (LDB) is also presented. The GUI includes physically accurate information about LID and also the lights' spectral power distributions (SPDs) so that a light-map can be generated for use with any sensor if the sensors luminosity function is known. Finally, for areas where more detail is required, a tool has been developed for editing and visualizing light effects over a 3D building from many light sources including area lights and windows. The above components are integrated in the PL tool to produce a night time urban view for not only a large-scale area but also a detail of a city building. iii