如何在R语言rayshader包的3D地图上添加多边形边界？

问题1：使用generate_polygon_overlay无法显示边界 #

核心原因是空间参考系（CRS）不匹配，以及generate_polygon_overlay参数设置需调整，按以下步骤修改：

1. 统一CRS
   检查并转换shp文件的CRS，使其与高程raster一致：

   # 查看raster的CRS
   crs(delhi_raster)
   # 转换shp的CRS匹配raster
   delhi_district_shp <- delhi_district_shp %>%
     st_transform(crs = crs(delhi_raster))
   

2. 正确生成多边形覆盖层
   指定线条颜色和宽度，确保覆盖层在高度图上清晰可见：

   polygon_layer <- generate_polygon_overlay(delhi_district_shp,
                                            extent = extent(delhi_raster),
                                            heightmap = delhi_mat,
                                            linewidth = 2,  # 增大线条宽度提升辨识度
                                            color = "black", # 选择与底图对比强烈的颜色
                                            palette = NULL) # 仅显示边界，不填充多边形
   

3. 重新绘制3D地图并添加覆盖层

   delhi_mat %>%
     height_shade(texture = grDevices::colorRampPalette(c("#9a133d","orange","red","purple"))(256)) %>%
     add_overlay(polygon_layer) %>%
     plot_3d(heightmap = delhi_mat,
             windowsize = c(800,800),
             solid = FALSE,
             zscale = 1,
             phi = 90,
             zoom = .6,
             theta = 0,
             shadowcolor = "grey50",
             linewidth = 6,
             background = "white",
             solidlinecolor = "#013b39")
   

问题2：osmdata无法获取行政边界数据 #

问题出在bbox格式错误和OSM特征筛选条件不正确，修正如下：

1. 修正bbox格式
   opq()要求的bbox顺序为c(minlon, minlat, maxlon, maxlat)，你之前的顺序颠倒了：

   # 正确提取extent顺序
   osm_bbox <- c(extent(delhi_raster)[1], extent(delhi_raster)[3],
                 extent(delhi_raster)[2], extent(delhi_raster)[4])
   

2. 正确筛选OSM行政边界
   要获取德里的区县边界，需筛选boundary="administrative"和对应层级（印度区县对应admin_level="6"）：

   raster_polygon_boundary <- opq(osm_bbox) %>%
     add_osm_feature(key = "boundary", value = "administrative") %>%
     add_osm_feature(key = "admin_level", value = "6") %>%
     osmdata_sf()
   

3. 使用OSM数据生成覆盖层
   从osmdata中提取多边形数据，再生成覆盖层：

   # 提取OSM多边形
   osm_districts <- raster_polygon_boundary$osm_multipolygons
   # 转换CRS匹配raster
   osm_districts <- osm_districts %>% st_transform(crs = crs(delhi_raster))
   # 生成覆盖层
   osm_polygon_layer <- generate_polygon_overlay(osm_districts,
                                                 extent = extent(delhi_raster),
                                                 heightmap = delhi_mat,
                                                 linewidth = 2,
                                                 color = "white")
   # 添加到3D地图
   delhi_mat %>%
     height_shade(texture = grDevices::colorRampPalette(c("#9a133d","orange","red","purple"))(256)) %>%
     add_overlay(osm_polygon_layer) %>%
     plot_3d(heightmap = delhi_mat,
             windowsize = c(800,800),
             solid = FALSE,
             zscale = 1,
             phi = 90,
             zoom = .6,
             theta = 0,
             shadowcolor = "grey50",
             linewidth = 6,
             background = "white",
             solidlinecolor = "#013b39")
   

内容的提问来源于stack exchange，提问作者ViSa