Method for making shaded relief map

Abstract

The invention relates to a method for making a shaded relief map. The method for making the shaded relief map comprises the following steps of: according to a digital elevation model of the relief, performing integral computation on a sky opening degree of each picture element; according to map making requirements, determining a total direct radiation ratio of the horizontal earth surface; setting an average reflectivity of an adjacent earth surface unit; computing a shading gray value of each picture element; enhancing the shading gray value of each picture element, such as linear enhancement, histogram equalization and the like; and generating the shaded relief map from the enhanced shading gray value of each picture element. In the method, by further increasing sky scattering and adjacent reflecting light sources to make the shaded relief map, the brightness of a shadow region can be improved and the relief information in the shadow region can be displayed; and the shading gray value is set according to the integrated illuminance of direct light, scattered light and adjacent reflecting light, so that the shading gray value is closer to a light effect in a natural environment, the defects of the single direct light can be made up, and the method is applicable for visually expressing the reliefs of mountainous areas with complicated reliefs and severe fluctuation.

Description

technical field [0001] The invention relates to a method for making a topography shading map. Background technique [0002] The landform shading method uses light to make each part of the landform produce different amounts of light to express the light and shade changes of the landform, and establishes the three-dimensional shape of the landform, which provides an important means for the analysis of the landform. [0003] At present, the light sources commonly used in the grayscale calculation of landform shading include direct lighting, Whitted overall lighting, and Phong lighting. The disadvantage of the direct lighting model is that when the light is obliquely incident, shadows will be generated, and the terrain information in the shadows cannot be expressed. The Whitted overall illumination model and the Phong illumination model further consider the ambient illuminance, but when applied, people often regard the local range of ambient light as consistent, and approximate...

AI Technical Summary

Problems solved by technology

[0004] The technical problem to be solved by the present invention is to overcome the deficiency that the topography shaded map using direct light source cannot express the terrain information in the shaded area in the prior art, and a method for making a topography shaded map under the condition of simulating natural light, which uses natural light It is divided into three light sources: direct sunlight, scattered light from the sky, and reflected light from adjacent slopes. Considering the comprehensive illuminance of the three light sources, the shading gray value of each surface unit is accurately calculated in order to simulate the natural environment to express terrain information. Terrain information in shaded areas

Images