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rgdal (version 1.6-7)

spTransform-methods: Methods for Function spTransform for map projection and datum transformation in package "rgdal"

Description

The spTransform methods provide transformation between datum(s) and conversion between projections (also known as projection and/or re-projection), from one unambiguously specified coordinate reference system (CRS) to another, prior to version 1.5 using Proj4 projection arguments. From version 1.5, Well-Known Text 2 (WKT2 2019) strings are used. For simple projection, when no Proj4 +datum tags are used, datum projection does not occur. When datum transformation is required, the datum should be defined with a valid value both in the CRS of the object to be transformed, and in the target CRS. In general datum is to be prefered to ellipsoid, because the datum always fixes the ellipsoid, but the ellipsoid never fixes the datum.

In addition, before version 1.5 the +towgs84 tag should have been used where needed to make sure that datum transformation would take place. Parameters for +towgs84 were taken from the legacy bundled EPSG file if they are known unequivocally, but could be entered manually from known authorities. Not providing the appropriate +datum and +towgs84 tags led to coordinates being out by hundreds of metres. Unfortunately, there is no easy way to provide this information: the user has to know the correct metadata for the data being used, even if this can be hard to discover.

From version 1.5, spTransform uses the modern PROJ coordinate operation framework for transformations. This avoids pivoting through WGS84 if possible, and uses WKT2 (2019) strings for source and target CRS often constructed from the bundled EPSG SQLite database. The database is searched for feasible candidate coordinate operations, and the most accurate available is chosen. More details are available in a vignette: vignette("CRS_projections_transformations").

Usage

get_transform_wkt_comment()
set_transform_wkt_comment(value)
get_enforce_xy()
set_enforce_xy(value)
get_last_coordOp()

Methods

"ANY"

default void method

"SpatialPoints", CRSobj = CRS

returns transformed coordinates of an "SpatialPoints" object using the projection arguments in "CRSobj", of class CRS

"SpatialPointsDataFrame", CRSobj = CRS

returns transformed coordinates of an "SpatialPointsDataFrame" object using the projection arguments in "CRSobj", of class CRS

"SpatialLines", CRSobj = CRS

returns transformed coordinates of an "SpatialLines" object using the projection arguments in "CRSobj", of class CRS

"SpatialLinesDataFrame", CRSobj = CRS

returns transformed coordinates of an "SpatialLinesDataFrame" object using the projection arguments in "CRSobj", of class CRS

"SpatialPolygons", CRSobj = CRS

returns transformed coordinates of an "SpatialPolygons" object using the projection arguments in "CRSobj", of class CRS

"SpatialPolygonsDataFrame", CRSobj = CRS

returns transformed coordinates of an "SpatialPolygonsDataFrame" object using the projection arguments in "CRSobj", of class CRS

"SpatialPixelsDataFrame", CRSobj = CRS

Because regular grids will usually not be regular after projection/datum transformation, the input object is coerced to a SpatialPointsDataFrame, and the transformation carried out on that object. A warning: “Grid warping not available, coercing to points” is given.

"SpatialGridDataFrame", CRSobj = CRS

Because regular grids will usually not be regular after projection/datum transformation, the input object is coerced to a SpatialPointsDataFrame, and the transformation carried out on that object. A warning: “Grid warping not available, coercing to points” is given.

Arguments

value

A non-NA logical value

Author

Roger Bivand Roger.Bivand@nhh.no

Examples

Run this code
set_thin_PROJ6_warnings(TRUE)
# state
data(state)
states <- data.frame(state.x77, state.center)
states <- states[states$x > -121,]
coordinates(states) <- c("x", "y")
proj4string(states) <- CRS("+proj=longlat +ellps=clrk66")
summary(states)
state.ll83 <- spTransform(states, CRS("+proj=longlat +ellps=GRS80"))
summary(state.ll83)
state.merc <- spTransform(states, CRS=CRS("+proj=merc +ellps=GRS80"))
summary(state.merc)
state.merc <- spTransform(states,
 CRS=CRS("+proj=merc +ellps=GRS80 +units=us-mi"))
summary(state.merc)
# NAD
if (FALSE) {
if (PROJis6ormore() || (!PROJis6ormore() && projNAD())) {
states <- data.frame(state.x77, state.center)
states <- states[states$x > -121,]
coordinates(states) <- c("x", "y")
proj4string(states) <- CRS("+init=epsg:4267")
print(summary(states))
state.ll83 <- spTransform(states, CRS("+init=epsg:4269"))
print(summary(state.ll83))
state.kansasSlcc <- spTransform(states, CRS=CRS("+init=epsg:26978"))
print(summary(state.kansasSlcc))
SFpoint_NAD83 <- SpatialPoints(matrix(c(-103.869667, 44.461676), nrow=1),
 proj4string=CRS("+init=epsg:4269"))
SFpoint_NAD27 <- spTransform(SFpoint_NAD83, CRS("+init=epsg:4267"))
print(all.equal(coordinates(SFpoint_NAD83), coordinates(SFpoint_NAD27)))
print(coordinates(SFpoint_NAD27), digits=12)
print(coordinates(SFpoint_NAD83), digits=12)
}
}
data(meuse)
coordinates(meuse) <- c("x", "y")
proj4string(meuse) <- CRS("+init=epsg:28992")
# see http://trac.osgeo.org/gdal/ticket/1987
summary(meuse)
meuse.utm <- spTransform(meuse, CRS("+proj=utm +zone=32 +datum=WGS84"))
summary(meuse.utm)
cbind(coordinates(meuse), coordinates(meuse.utm))
if (FALSE) {
# Kiritimati
kiritimati_primary_roads <- readOGR(system.file("vectors",
 package = "rgdal")[1], "kiritimati_primary_roads")
kiritimati_primary_roads_ll <- spTransform(kiritimati_primary_roads,
 CRS("+proj=longlat +datum=WGS84"))
opar <- par(mfrow=c(1,2))
plot(kiritimati_primary_roads, axes=TRUE)
plot(kiritimati_primary_roads_ll, axes=TRUE, las=1)
par(opar)
# scot_BNG
scot_BNG <- readOGR(system.file("vectors", package = "rgdal")[1],
   "scot_BNG")
scot_LL <- spTransform(scot_BNG, CRS("+proj=longlat +datum=WGS84"))
plot(scot_LL, axes=TRUE)
grdtxt_LL <- gridat(scot_LL)
grd_LL <- gridlines(scot_LL, ndiscr=100)
summary(grd_LL)
target <- CRS(proj4string(scot_BNG))
grd_BNG <- spTransform(grd_LL, target)
grdtxt_BNG <- spTransform(grdtxt_LL, target)
opar <- par(mfrow=c(1,2))
plot(scot_BNG, axes=TRUE, las=1)
plot(grd_BNG, add=TRUE, lty=2)
text(coordinates(grdtxt_BNG),
   labels=parse(text=as.character(grdtxt_BNG$labels)))
par(opar)
}
# broke_proj
broke_proj <- FALSE
# https://github.com/OSGeo/PROJ/issues/1525
pv <- .Call("PROJ4VersionInfo", PACKAGE="rgdal")[[2]]
if (pv >= 600 && pv < 620) broke_proj <- TRUE
if (!broke_proj) { 
crds <- matrix(data=c(9.05, 48.52), ncol=2)
spPoint <- SpatialPoints(coords=crds,
 proj4string=CRS("+proj=longlat +ellps=sphere +no_defs"))
ob_tran_def <- paste("+proj=ob_tran +o_proj=longlat",
 "+o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +ellps=sphere +no_defs")
tg <- CRS(ob_tran_def)
# proj4string not propagated in GDAL 3.0.0
a <- spTransform(spPoint, tg, use_ob_tran=TRUE)
a
}
#should be (-5.917698, -1.87195)
if (!broke_proj) {
spTransform(a, CRS("+proj=longlat +ellps=sphere +no_defs"),
 use_ob_tran=TRUE)
}
if (!broke_proj) {
try(spTransform(a, CRS(paste("+proj=tmerc +lat_0=0 +lon_0=9 +k=1",
"+x_0=3500000 +y_0=0 +ellps=bessel +units=m +no_defs")),
 use_ob_tran=TRUE))
}
if (!broke_proj) {
spTransform(spPoint, CRS(paste("+proj=tmerc +lat_0=0 +lon_0=9 +k=1",
"+x_0=3500000 +y_0=0 +ellps=bessel +units=m +no_defs")))
}
if (!broke_proj) {
spTransform(spTransform(a, CRS("+proj=longlat +ellps=sphere +no_defs"),
 use_ob_tran=TRUE), CRS(paste("+proj=tmerc +lat_0=0 +lon_0=9 +k=1",
"+x_0=3500000 +y_0=0 +ellps=bessel +units=m +no_defs")))
}
crds1 <- matrix(data=c(7, 51, 8, 52, 9, 52, 10, 51, 7, 51), ncol=2,
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
crds2 <- matrix(data=c(8, 48, 9, 49, 11, 49, 9, 48, 8, 48), ncol=2,
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
crds3 <- matrix(data=c(6, 47, 6, 55, 15, 55, 15, 47, 6, 47), ncol=2,
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
spLines <- SpatialLines(list(Lines(list(Line(crds1), Line(crds2),
Line(crds3)), ID="a")));
slot(spLines, "proj4string") <- CRS("+proj=longlat +ellps=sphere +no_defs");
bbox(spLines);
if (!broke_proj) {
spLines_tr <- spTransform(spLines, tg, use_ob_tran=TRUE);
bbox(spLines_tr)
}
if (!broke_proj) {
bbox(spTransform(spLines_tr, CRS("+proj=longlat +ellps=sphere"),
 use_ob_tran=TRUE))
}
if (!broke_proj) {
spPolygons <- SpatialPolygons(list(Polygons(list(Polygon(crds1),
Polygon(crds2), Polygon(crds3)), ID="a")));
slot(spPolygons, "proj4string") <- CRS("+proj=longlat +ellps=sphere +no_defs");
bbox(spPolygons);
}
if (!broke_proj) {
spPolygons_tr <- spTransform(spPolygons, tg, use_ob_tran=TRUE);
bbox(spPolygons_tr)
}
if (!broke_proj) {
bbox(spTransform(spPolygons_tr, CRS("+proj=longlat +ellps=sphere"),
 use_ob_tran=TRUE))
}
# added after posting by Martin Ivanov
if (FALSE) {
data(nor2k)
summary(nor2k)
nor2kNGO <- spTransform(nor2k, CRS("+init=epsg:4273"))
summary(nor2kNGO)
all.equal(coordinates(nor2k)[,3], coordinates(nor2kNGO)[,3])
# added after posting by Don MacQueen 
crds <- cbind(c(-121.524764291826, -121.523480804667), c(37.6600366036405, 37.6543604613483))
ref <- cbind(c(1703671.30566227, 1704020.20113366), c(424014.398045834, 421943.708664294))
crs.step1.cf <- CRS(paste("+proj=lcc +lat_1=38.43333333333333",
 "+lat_2=37.06666666666667 +lat_0=36.5 +lon_0=-120.5",
 "+x_0=2000000.0 +y_0=500000.0 +ellps=GRS80 +units=us-ft +no_defs",
 "+towgs84=-0.991,1.9072,0.5129,0.025789908,0.0096501,0.0116599,0.0"))
locs.step1.cf <- spTransform(SpatialPoints(crds,
 proj4string=CRS("+proj=longlat +datum=WGS84")), crs.step1.cf)
suppressWarnings(proj4string(locs.step1.cf) <- CRS(paste("+proj=lcc",
"+lat_1=38.43333333333333 +lat_2=37.06666666666667 +lat_0=36.5",
"+lon_0=-120.5 +x_0=2000000.0 +y_0=500000.0 +ellps=GRS80 +units=us-ft",
"+no_defs +nadgrids=@null")))
locs.step2.cfb <- spTransform(locs.step1.cf, CRS("+init=epsg:26743"))
coordinates(locs.step2.cfb) - ref
all.equal(unname(coordinates(locs.step2.cfb)), ref)
}
if (FALSE) {
# new_proj_and_gdal()
run <- new_proj_and_gdal()
if (run) {
# Test for UTM == TMERC (<= 4.9.2) or UTM == ETMERC (> 4.9.2)
nhh <- SpatialPointsDataFrame(matrix(c(5.304234, 60.422311), ncol=2),
 proj4string=CRS(SRS_string="OGC:CRS84"), data=data.frame(office="RSB"))
nhh_utm_32N_P4 <- spTransform(nhh, CRS("+init=epsg:3044"))
nhh_tmerc_P4 <- spTransform(nhh, CRS(paste("+proj=tmerc +k=0.9996",
 "+lon_0=9 +x_0=500000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs")))
nhh_etmerc_P4 <- spTransform(nhh, CRS(paste("+proj=etmerc +k=0.9996",
 "+lon_0=9 +x_0=500000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs")))
all.equal(coordinates(nhh_utm_32N_P4), coordinates(nhh_tmerc_P4),
 tolerance=1e-9, scale=1)
# UTM == TMERC: PROJ4 <=4.9.2
all.equal(coordinates(nhh_utm_32N_P4), coordinates(nhh_etmerc_P4),
 tolerance=1e-9, scale=1)
# UTM == ETMERC: PROJ4 > 4.9.2
unis <- SpatialPointsDataFrame(matrix(c(15.653453, 78.222504), ncol=2),
 proj4string=CRS(SRS_string="OGC:CRS84"), data=data.frame(office="UNIS"))
unis_utm_33N_P4 <- spTransform(unis, CRS("+init=epsg:3045"))
unis_tmerc_P4 <- spTransform(unis, CRS(paste("+proj=tmerc +k=0.9996 +lon_0=15",
 "+x_0=500000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs")))
unis_etmerc_P4 <- spTransform(unis, CRS(paste("+proj=etmerc +k=0.9996",
 "+lon_0=15 +x_0=500000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs")))
all.equal(coordinates(unis_utm_33N_P4), coordinates(unis_tmerc_P4),
 tolerance=1e-9, scale=1)
# UTM == TMERC: PROJ4 <=4.9.2
all.equal(coordinates(unis_utm_33N_P4), coordinates(unis_etmerc_P4),
 tolerance=1e-9, scale=1)
# UTM == ETMERC: PROJ4 > 4.9.2
}
}

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