I am trying to overlay 2 spatial objects using the plot() function. I understand that the projections of the 2 objects (of class SpatialLinesDataFrame and SpatialPolygonsDataFrame) need to be the same in order to have them visualized in the same plot. I've found similar questions here and here, but none of these can help me what I want to achieve.
Here's the coding for the SpatialPolygonsDataFrame. (v.map is a list of .kml files and loccoor is an object that stores location and corresponding x and y coordinates):
map.l<-list()
for (i in 1:length(v.map)){
ll<-ogrListLayers(paste(loccoor,"/",v.map[i],".kml",sep=""))
shp<-readOGR(paste(loccoor,"/",v.map[i],".kml",sep=""),layer=ll)
map<-spTransform(shp, CRS("+proj=longlat +datum=WGS84"))
map.l[[i]]<-map
}
plot(map.l[[1]],xlim=c(min(coor[,3]),max(coor[,3])),
ylim=c(min(coor[,2]),max(coor[,2])))
for (i in 2:length(v.map)){
plot(map.l[[i]],xlim=c(min(coor[,3]),max(coor[,3])),
ylim=c(min(coor[,2]),max(coor[,2])),add=T)
}
projection SpatialPolygonsDataFrame "map": "+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0"
projection SpatialLinesDataFrame "contours": "+proj=aeqd +ellps=WGS84 +lon_0=-XX.XXXXX +lat_0=XX.XXXXX".
I want to transform the projection of the "map" object to match that of the "contours". Simply replacing the "CRS("+proj=longlat +datum=WGS84")" of the "map" object with the projection of the "contours" object doesn't seem to work, because then the polygons are no longer plotted (visible).
Any thoughts to this would be greatly appreciated!
Here's a not very great metaphor: The coordinates are like directions, and the crs tells us what language the directions are in. So, if you change the crs, but you leave the coordinates as they are, then it would be like trying to read German directions with a Spanish dictionary.
We can translate the directions from one crs to another using sp::spTransform().
The function takes two arguments: a spatial object, and a crs.
We can use raster::crs() to get the crs from the another spatial object. So, to transform the map's coordinates (and crs) to the crs of the contours:
map <- spTransform(map, crs(contours))
Related
I have a dataset form the public repo https://github.com/highsource/verbundkarte
Reading the dataset with st_read and plotting it with ggplot yields a beautiful map with correct lng and lat data.
df <- st_read("~/Verkehrsverbunde.shp")
map <- ggplot(df) + geom_sf(aes(fill=SHORTNAME))
I therefore assume, that the lng/lat values are included in the variable df$geometry. However, if I use leaflet, no matter what I try I end up with an error. For instance
df%>% leaflet() %>%
addProviderTiles("CartoDB") %>%
addPolygons(label = htmlEscape(verbunddaten$SHORTNAME)) %>%
setView(lng = 10.3, lat = 51.9, zoom = 5.1)
ends up with
Warning messages:
1: sf layer is not long-lat data
2: sf layer has inconsistent datum (+proj=tmerc +lat_0=0 +lon_0=9 +k=1 +x_0=3500000 +y_0=0 +datum=potsdam +units=m +no_defs ).
Need '+proj=longlat +datum=WGS84'
I found this beautiful conversation of which I understood basically nothing. Reading the data with readOGR as suggested here doesn't solve my problem.
How do I force leaflet to assume the same longlat and EPSG as ggplot?
The data in your Verkehrsverbunde.shp shapefile is in a custom traverse mercator projection, where coordinates are expressed in meters. By contrast, r-leaflet expects data to be expressed in degrees of latitude-longitude, which would look like an equirectangular projection if/when plotted.
I'll guess that, contrary to your belief, ggplot is not using latitude and longitude in degrees, but rather northing and easting values in meters. The representation of the data might look similar for small areas.
In GIS terms, your data is using the EPSG:31467 CRS (Coordinate Reference System), as can be inferred by proj=tmerc and datum=postdam; r-leaflet expects data in the EPSG:4326 CRS.
The approach here would be to reproject your data, so that coordinates are in latitude-longitude as expected. There are plenty of ways to do this; running ogr2ogr -t_srs epsg:4326 Verkehrsverbunde-latlng.shp Verkehrsverbunde-latlng.shp on a command line, using R, or using QGIS, amongst other methods.
I have a map with an elevation raster that is in lat/long coordinates but I now need to display the map in easting/northing. How can I accomplish this?
I have tried reprojecting the raster from lat/long to UTM but this warps the map (I assume for reasons discussed in this SO post).
A minimal working example follows a description of the code that I am using to produce the map in lat/long coordinates. I used a manually defined bounding box, extent, to download the elevation raster of interest from FedData. I then plotted the raster using tmap.
# - Libraries ----
library(proj4)
library(FedData)
library(rgdal)
library(tmap)
# extent defined manually
extent <- rgeos::readWKT("POLYGON((-118.25 36.45, -118.25 36.6, -118.25 36.9, -118.8 36.9, -118.8 36.45, -118.25 36.45))")
# define shape polygon on lat/long coordinates
proj4string(extent) <- "+proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs"
# - Get national elevation raster ----
# download National Elevation Database elevation data in extent
# default resolution is 1 arcsecond (res="1);
# to get 1/3 arcsecond (res="13)
ned_raster<-FedData::get_ned(template=extent, label="ned_raster", res="1", force.redo = T)
# - Plot with tmap ----
tm_shape(ned_raster,unit.size=1)+
tm_graticules() +
tm_raster(legend.show=FALSE)
Update I'm updating the question with some additional clarification after Robert Hijmans' answer. I am including the code that I used for the reprojection here:
ned_raster2 <- raster::projectRaster(ned_raster, crs=CRS("+proj=utm +init=epsg:26711 +zone=11 +north +no_defs"))
The output is comparable to the one in the map you included in your answer. By modifying the bounding box with tmaptools::bb I can clip the map with tmap so that the projection is correct but it does not "appear" warped:
# - Project from angular to planar ----
ned_raster2 <- raster::projectRaster(ned_raster, crs=CRS("+proj=utm +init=epsg:26711 +zone=11 +north +no_defs"))
# redefine extent/bounding box
e2 = tmaptools::bb(ned_raster2)
e2 = e2*c(1.01,1.001,.99,.999)
# - Plot with tmap ----
tm_shape(ned_raster2,unit.size=1,bbox=e2)+
tm_graticules(n.x=5) +
tm_raster(legend.show=FALSE)
From this, how can I include the appropriate axes (in easting/northing) on this map?
I now need to display the map in easting/northing.
I understand that in stead of angular (lon/lat) coordinates you want to use planar (Cartesian) coordinates. That means that you need to choose an appropriate coordinate reference system (CRS). You say you used UTM, and that could be reasonable, but you found that the results are "warped". You should show the code you used because you probably made a mistake. There always is some distortion, but for a small area like this is would not be an issue if you specify the CRS correctly. (otherwise, explain "warped" and why it matters.)
For example
library(raster)
library(FedData)
# extent defined manually
e <- as(extent(-118.8, -118.25, 36.45, 36.9), "SpatialPolygons")
crs(e) <- "+proj=longlat"
ned <- FedData::get_ned(template=e, label="ned_raster", res="1", force.redo = T)
ned2 <- projectRaster(ned, crs="+proj=utm +zone=11")
plot(ned2)
For larger areas you cannot use UTM and you would need to use another CRS.
Alternatively, you could create grid-lines (graticule) from the projected raster, store their coordinates, and transform these back to longlat. That would be a bit odd. Normally, one might want to show longlat coordinates on a otherwise projected (planar) map.
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?
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"))
I have hundreds of shapefiles without a coordinate reference system. My goal is the overlay the spatial polygons over the WorldClim raster layer. I used this approach before without any problems. However, this time the coordinates from my shapefiles are strange for me. Each coordinate for bounding box and coords within polygons is composed of 8 digit numbers without comma or dot to separate de decimals.
This is the bounding box from one of the shapes:
SHP bbox: xmin:-17367529, xmax:17367529, ymin:-5997367 and ymax:7052489
which are clearly different from the bounding box of the WorldClim raster layer.
WorldClim bbox: xmin=-180,xmax=180,ymin=-60 and ymax=90
When I tried to overlay the shapefile over the raster layer using plot command nothing happens.
plot(shapefile, add=T)
I understood that this is a projection problem. Then I tried to assign the same coordinate system of the WorldClim raster layer in the shapefile using the CRS function. However, the result remains the same (i.e. the shapefiles do not over the raster). In the sequence, I tried to use the spTransform function from the rgdal package to reproject the shapefile coordinates. However, because shapefile does not have any reference system the function does not work and I do not know how to reproject the shapefile in order to match with the raster layer. I've been researching for a few days about how to deal with this problem and I believe that the absence of a reference system is a key point to the problem. However, I'm failing to overcome this problem and I would like to know if someone could help how to deal with this situation.
You need to define the projection of shape files first using proj4string(meuse) or crs(shapefile)<-crs string then you can use spTransform:
library(rgdal)
data(meuse)
coordinates(meuse) <- c("x", "y")
Here you have the spatial data with x and y but you do not have the crs yet! So if you use spTransform it will fail.
summary(meuse) #proj4string : [NA] so below line fails!
meuse.utm <- spTransform(meuse, CRS("+proj=utm +zone=32 +datum=WGS84"))
# Error in spTransform(xSP, CRSobj, ...) :
# No transformation possible from NA reference system
To get around this, as mentioned above, you first need to define the projection as below:
proj4string(meuse) <- CRS(paste("+init=epsg:28992",
"+towgs84=565.237,50.0087,465.658,-0.406857,0.350733,-1.87035,4.0812"))
summary(meuse) #proj4string : epsg:28992... and then you may use spTransform
and then:
meuse.utm <- spTransform(meuse, CRS("+proj=utm +zone=32 +datum=WGS84"))
I'm trying to use R to perform a map of interpolated frequencies of data collected from Iberian Peninsula. (something like this https://gis.stackexchange.com/questions/147660/strange-spatial-interpolation-results-from-ordinary-kriging )
My problem is that the plot is not showing the interpolated data, due to some kind of error in the atributte new_data of the autokrige function.
https://cran.r-project.org/web/packages/automap/automap.pdf
new_data:
A sp object containing the prediction locations. new_data can be a points set, a
grid or a polygon. Must not contain NA’s. If this object is not provided a default is calculated. This is done by taking the convex hull of input_data and placing around 5000 gridcells in that convex hull.
I think the problem is that R is not reading well the map transformed to poligons because if I avoid this new_data attribute I get a propper plot of the krigging values. but I do not obtain a good shape of the iberian peninsula.
Can someone help me please? I would be truly grateful
here you can see my data: http://pastebin.com/QHjn4qjP
Actual code:
now since I transform my data coordinates to UTM projection i do not get error messages but the last plot is not interpolated, the whole map appear of one single color :(
setwd("C:/Users/Ruth/Dropbox/R/pruebas")
#Libraries
library(maps)
library(mapdata)
library(automap)
library(sp)
library(maptools)
library(raster)
library(rgdal)
####################MAPA#############
#obtain the grid of the desired country
map<-getData('GADM', country='ESP', level=0)
#convert the grid to projected data
mapa.utm<-spTransform(mapa3,CRSobj =CRS(" +proj=utm +zone=29 +zone=30 +zone=31 +ellps=WGS84"))
###############################Datos#######################
#submit the data
data1<-read.table("FRECUENCIASH.txt",header=T)
head(data1)
attach(data1)
#convert longlat coordinates to UTM
coordinates(data1)<-c("X","Y")
proj4string(data1) = CRS("+proj=longlat +datum=WGS84")
data1.utm=spTransform(data1, CRS("+proj=utm +zone=29 +zone=30 +zone=31 +ellps=WGS84 "))
######################Kriging interpolation #####################
#Performs an automatic interpolation
kriging_result<-autoKrige(Z~1,data1.utm,mapa.utm,data_variogram = data1.utm)
#Plot the kriging
result1<-automapPlot(kriging_result$krige_output,"var1.pred",sp.layout = list("sp.points", data1.utm));result1
result2<-plot(kriging_result);result2
The error you get is related to the fact you are using unprojected data as input for automap. Automap can only deal with projected data. Googling for map projections should give you some background information. To project your data to a suitable projection, you can use spTransform from the sp package.
The fact that it works without newdata is because in that object the projection is not set, so automap cannot warn you. However, the results of automap with latlon input data is not reliable.