the islamic calendar is based on lunar months, which begin when the thin crescent moon is actually sighted in the western sky after sunset within a day or so after the new moon. the islamic dates begin at sunset on the previous day. the visibility of the lunar crescent as a function of the moon's age - the time counted from the new moon - is obviously of great importance to muslims. the da...

Air pollution is one of the most important problems in the world’s major cities in the last century because it endangers human health and the environment. One of the indicators of air pollution is nitrogen dioxide, which is continuously measured by satellite from space and via ground-based instruments. In this paper, the data for nitrogen dioxide was measured by OMI over Tehran. Wind, surface t...

atmospheric visibility has been defined as the greatest distance at which an observer can see a black object viewed against the horizon sky, which in quantitative terminology is known as visual range. visibility, in the absence of special meteorological events (e.g. rain and fog), is an excellent indicator of air quality. visibility impairment results from light scattering and absorption by atm...

From-region visibility culling is considered significantly harder than from-point visibility culling, since it is inherently 4dimensional. We present a conservative occlusion culling method based on factorizing the 4D visibility problem into horizontal and vertical components. The visibility of the two components is solved asymmetrically: the horizontal component is based on a novel parameteriz...

We present a fast conservative from-region visibility method capable of handling 3D models using arbitrary 3D triangles as occluders. The from-region visibility problem is considered significantly harder than the from-point visibility problem, since it is inherently 4-dimensional. Our occlusion culling method is based on factorizing the 4D visibility problem into horizontal and vertical compone...