使用 tmap 绘制空间点数据的问题

Question

I have created a class Large SpatialPointDataFrame from a csv file, and I am trying to plot the data points using tmap. When I plotted the SpatialPointDataFrame using plot(), everything looked fine. However, when I tried to plot it using tmap, it only shows one single point plus it is not where it should be, btw, the point that got shown is the last item in the data frame. I'm thinking there might be something wrong with my projecton? CRS(Using SVY21 or EPSG:3414) properties of the SpatialPointDataFrame:

crs: +init=epsg:3414 +proj=tmerc +lat_0=1.366666666666667 +lon_0=103.8333333333333 +k=1 +x_0=28001.642 +y_0=38744.572 +ellps=WGS84 +units=m +no_defs

This is how I converted the dataframe to a spatialpointdataframe, where listing is the original dataframe read from a csv file.

coords <- listing[ , c("latitude", "longitude")]
crs <- CRS("+init=epsg:3414")
listing_sp <- SpatialPointsDataFrame(coords = coords, listing, proj4string = crs)

Any suggestions on how I should debug?

Answer 1

In your code, where you have crs <- CRS("+init=epsg:3414") , you are assigning a projection but your source data has not yet been transformed to that projection. If your source data is in lat/lon it's meant to be used with the WGS84 projection ( epsg code 4326 ).

Once you create your spatialPointDataFrame using the projection matching your coordinates, you simply have to reproject using spTransform . To reproject to SVY21, you still need to transform. Can't test without some reproducible data but it should look like this.

coords <- listing[ , c("latitude", "longitude")]
crs <- CRS("+init=epsg:4326")
listing_sp <- SpatialPointsDataFrame(coords = coords, listing, proj4string = crs)
listing_sp_svy21 <- spTransform(listing_sp, CRS("+init=epsg:3414"))