Application of Relief Shading Method in Meteorological Model Data Visualization
By introducing the relief shading method,which is often used in making the topographic maps,into the visualisation of numerical weather forecast data,this article presents the achievement in three-dimensional drawing of meteorological variables,such as air pressure and geopotential height.Based on the principle and implementation of hill shading,which uses the relationship between the illumination angle,the direction,the slope,and the orientation of the terrain to calculate the brightness value of luminous flux,the relief shading method makes use of the brightness value to display the three-dimensional sense of meteorological model data.At the same height,the steeper the terrain,the darker(brighter)the shaded(sunny)side;under the same slope,the higher the terrain,the darker(brighter)the shaded(sunny)side,which is consistent with the real-life visual effect.The colouring method of the shaded relief map is to use the brightness value(V)in the HSV colour space which is calculated on each grid point,combined with hue(H)and saturation(S)to obtain a complete HSV colour scheme.Through the conversion from the HSV colour space to the RGB colour space,the latter colour space is used for drawing a coloured shaded relief map for meteorological model data.In the shaded relief map,the high-pressure centre in the weather system is often shown as a raised peak,and the low pressure is shown as a depressed valley;a large pressure gradient can be seen as a steep slope,while a small pressure gradient can be seen as a gentle slope.Compared with the traditional isoline and colour filling analysis,it is found that the shaded relief map can help to identify high-low weather systems by concave-convex shapes and reflects the gradient changes of weather systems through the steepness of slope,thus intuitively representing the three-dimensional distribution of atmospheric circulation.In addition,the shaded relief map has the ability to visualise model data in pixel level details,identify early eddy current disturbances in small gradients,and reveal equivalent terrain effects,which helps the meteorologists better interpret the model data and provides the references for the improvements of data process functions in numerical models.Furthermore,the relief shading method is suitable for using the synthetic animations to showcase the fluid characteristics of atmospheric motion,which is conducive to popularising the concept of various weather systems,such as the high,the low,the trough and ridge,and their evolution to the public.
relief shadingnumerical weather forecast datathree-dimensional visualizationHue-Saturation-Value(HSV)color space
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