Question

我正在关注如何从Here将PostGIS中的空间数据转换为R的完美示例。该示例非常有效，但是当我尝试检索更大的数据集（＆gt; 1000rows）时，事情变慢了。这可能是每次必须进行的新内存分配（只是猜测）。有没有办法在循环之前设置spTemp的大小？完整代码供参考：

library(RPostgreSQL)
library(rgeos)
library(sp)

# Load data from the PostGIS server
conn = dbConnect(
  dbDriver("PostgreSQL"), dbname=dbname, host=host, port=5432, 
  user=user, password=password
  )

strSQL = "
  SELECT gid, ST_AsText(geom) AS wkt_geometry, attr1, attr2[, ...]
  FROM geo_layer"
dfTemp = dbGetQuery(conn, strSQL)
row.names(dfTemp) = dfTemp$gid

# Create spatial polygons
# To set the PROJ4 string, enter the EPSG SRID and uncomment the 
# following two lines:
# EPSG = make_EPSG()
# p4s = EPSG[which(EPSG$code == SRID), "prj4"]
for (i in seq(nrow(dfTemp))) {
  if (i == 1) {
    spTemp = readWKT(dfTemp$wkt_geometry[i], dfTemp$gid[i])
    # If the PROJ4 string has been set, use the following instead
    # spTemp = readWKT(dfTemp$wkt_geometry[i], dfTemp$gid[i], p4s)
  }
  else {
    spTemp = rbind(
      spTemp, readWKT(dfTemp$wkt_geometry[i], dfTemp$gid[i])
      # If the PROJ4 string has been set, use the following instead
      # spTemp, readWKT(dfTemp$wkt_geometry[i], dfTemp$gid[i], p4s)
    )
  }
}

# Create SpatialPolygonsDataFrame, drop WKT field from attributes
spdfFinal = SpatialPolygonsDataFrame(spTemp, dfTemp[-2])

在R中预分配SpatialPolygonsDataFrame

0 个答案: