Shaded Relief from LiDAR (Image Service)

This shaded relief image was generated from the lidar-based bare-earth digital elevation model (DEM). A shaded relief image provides an illustration of variations in elevation using artificial shadows. Based on a specified position of the sun, areas that would be in sunlight are highlighted and areas that would be in shadow are shaded. In this instance, the position of the sun was assumed to be 45 degrees above the northwest horizon. The shaded relief image shows areas that are not in direct sunlight as shadowed. It does not show shadows that would be cast by topographic features onto the surrounding surface. Using ERDAS IMAGINE, a 3X3 neighborhood around each pixel in the DEM was analyzed, and a comparison was made between the sun's position and the angle that each pixel faces. The pixel was then assigned a value between -1 and +1 to represent the amount of light reflected. Negative numbers and zero values represent shadowed areas, and positive numbers represent sunny areas. In ArcGIS Desktop 10.7.1, the image was converted to a JPEG 2000 format with values from 0 (black) to 255 (white). See the MassGIS datalayer page to download the data as a JPEG 2000 image file. View this service in the Massachusetts Elevation Finder. MassGIS has also published a Lidar Shaded Relief tile service (cache) hosted in ArcGIS Online.

本阴影晕渲图像由基于激光雷达（LiDAR）的裸地数字高程模型（DEM）生成。阴影晕渲图像通过人工阴影直观呈现高程变化特征：依据预设的太阳方位，将受光区域高亮显示，受阴影遮挡的区域则以阴影标注。本示例中，太阳方位设定为西北地平线以上45度。该阴影晕渲图仅展示未直接受光的阴影区域，并不显示地形要素向周边地表投射的阴影。
研究人员借助ERDAS IMAGINE软件，对数字高程模型中每个像素周围的3×3邻域进行分析，比对太阳方位与各像素的朝向角度，并为每个像素赋值于-1至+1之间，以表征其反射光量。其中负值与零值代表阴影区域，正值代表受光区域。
在ArcGIS Desktop 10.7.1软件中，该图像被转换为JPEG 2000格式，其灰度取值范围为0（黑色）至255（白色）。用户可访问马萨诸塞州地理信息系统（MassGIS）数据图层页面，下载该JPEG 2000格式的图像文件。
亦可通过马萨诸塞州高程查找器查看该服务。
此外，MassGIS还发布了托管于ArcGIS Online平台的激光雷达阴影晕渲瓦片缓存服务。