How to import OSM polygons data from PostGIS to R? - r

Question

I am new to the world of spatial analysis using R. Using this link I have downloaded OSM data in .osm.pbf format. Then I used osm2pgsql tool to get data in PostgreSQL (PostGIS extension). Now I have several tables in my database and I want to access the polygons table in R and then perform spatial analysis on the polygon vector data. I have been searching around allot but am not able to import required data in R. I found this tutorial quite similar to what I am looking for but its in Python. I want to access polygon data from PostGIS using R.
Therefore, essentially I would like to know interaction of R with PostGIS. Can anybody recommend me any book on this topic? Since I couldn't find a blog or tutorial so far that works for me on my Windows 10 64-bit machine.
Thanks for your time and looking forward for the suggestions.

Answer 1

I have still not found a way to get required data form PostGIS using rgdal package available in R. Probably it is because of my OS issues. (I am not exactly sure as I am not an expert). But I have found an alternative to rgdal and it has done exactly what I wanted it to do. The code is as following:
library(RPostgreSQL)
library(rgeos)
library(sp)
# Load data from the PostGIS server
conn = dbConnect(
dbDriver("PostgreSQL"), dbname="dbNAME", host="localhost", port=5432,
user="username", password="pw"
)
strSQL = "SELECT osm_id, name, area, highway, railway, place, ST_AsText(way) AS wkt_geometry FROM table"
df = dbGetQuery(conn, strSQL)
#Geomtery column as R list
geo_col = df$wkt_geometry
polygon_list = suppressWarnings(lapply(geo_col, function(x){
x <- gsub("POLYGON\\(\\(", "", x)
x <- gsub("\\)", "", x)
x <- strsplit(x, ",")[[1]]
#Now each polygon has been parsed by removing POLYGON(( from the start and )) from the end
#Now for each POLYGON its xValues and yValues are to be extracted to for Polygon object
xy <- strsplit(x, " ")
v_xy = suppressWarnings(sapply(xy, function(p){
xValue = p[1]
yValue = p[2]
vec = c(xValue, yValue)
}))
#Now we have all x values in first column of v_xy and all y values in second column of v_xy
#Let us make the Polygon object now
p_xvalues = as.numeric(v_xy[1, ])
p_yvalues = as.numeric(v_xy[2, ])
p_object <- Polygon(cbind(p_xvalues, p_yvalues))
}))
#Now we have all of the polygons in polygon object format
#Let us join it with main data frame, i.e. df
df$object_polygon <- polygon_list
#View(df)
#Now Let us form SpatialPolygons() object out of it
Ps_list = list()
for (i in seq(nrow(df))) {
Ps_list[[i]] <- Polygons(polygon_list[i], ID=df[i,][1])
}
SPs = SpatialPolygons(Ps_list)
#Now FINALY its the time to form SpatialPolygonsDataFrame
row.names(df) = df$osm_id
SPDF = SpatialPolygonsDataFrame(Sr = SPs, data = df[, 1:6], match.ID = TRUE)
Therefore, essentially I had to write a parser to get the required data which readOGR() does it one line.

Answer 2

I dont know R, but very familiar with postgis. Postgis is just SQL functions, if you can use Select you can access postgis,
So if you want access polygon just create new function in postgres.
But if you want display polygons you need check with R what function are available, i usually use Openlayer javascript api to show my results in the webpage.