基于聚焦滤波的林业专题地图制图综合方法

Cartographic Generalization Approach of Forestry Thematic Mapping Based on Focal Filtering

森林资源规划设计调查成果总是以连续的面状图斑呈现。当大比例尺二类调查成果图缩编为更小比例尺地图时,常常需要制图综合。如何在制图综合时既要简化多边形边界,又要保持各类型林相面积和位置的相对不变,是林业专题制图的一个难题。经大量实验发现,将实施制图综合的连续面状图斑要素从矢量格式转换为栅格格式,经Focal滤波器以Majority方式滤波处理后,再将滤波后结果从栅格数据转换为矢量数据,可较好地实现森林资源专题连续面状要素信息的制图综合。以云南省某地一个1万hm^(2)的实验区为例,使用该方法将1∶2.5万的森林资源二类调查成果图缩编为1∶25万。结果表明,缩编后,多边形边界简化,目视效果较好,各类型林相面积变化绝对值平均为0.2%,位置精确度平均值为94.68%。此方法已应用于云南森林资源状况图集相关专题图等的生产实践。

The results of forest resources planning and design survey are always presented in continuous planar patches.When the large-scale result map is reduced to the smaller-scale map,cartographic generalization is often required.How to simplify the polygon boundary and keep the area and position of various objects relatively unchanged during cartography generalization is still a challenge.A large number of experiments found that the continuous planar patches was converted from vector format to raster format,then the focal majority filter was performed on the raster data in Majority manner to convert the filtered raster data to vector format for thematic mapping,which could effectively achieve cartographic generalization of forest resource thematic continuous planar feature information.This approach was used to reduce the 1∶25000 forest inventory map to a 1∶250000 map over the 10000 hm^(2) study area in Yunnan.The results showed that after reduction,the polygonal boundaries were simplified,and the visual effect was good.The average absolute area change of each land use type was 0.2%,and the average positional accuracy was 94.68%.This approach has been widely used in the production practice of relevant thematic maps of Yunnan forest resources atlas.