rgdal (version 1.3-2)

project: Projection of coordinate matrices

Description

Interface to the PROJ.4 library of projection functions for geographical position data, no datum transformation possible. Use spTransform() for extended support.

Usage

project(xy, proj, inv = FALSE, use_ob_tran=FALSE, legacy=TRUE)

Arguments

xy

2-column matrix of coordinates

proj

character string of projection arguments; the arguments must be entered exactly as in the PROJ.4 documentation, in particular there cannot be any white space in +<arg>=<value> strings, and successive such strings can only be separated by blanks.

inv

default FALSE, if TRUE inverse projection to geographical coordinates

use_ob_tran

default FALSE, if TRUE and “+proj=ob_tran”, use General Oblique Transformation with internalised from/to projection reversal; the user oblique transforms forward rather than inverse.

legacy

default TRUE, if FALSE, use transform C functions (enforced internally for Windows 32-bit platforms)

Value

A two column matrix with projected coordinates.

Details

Full details of projection arguments available from website below, and examples in file "epsg" in the data directory installed with PROJ.4.

Note that from PROJ.4 4.9.3, the definition of UTM is changed from TMERC to ETMERC; see example.

References

http://proj.maptools.org/

See Also

CRS-class, spTransform-methods

Examples

# NOT RUN {
data(state)
res <- project(cbind(state.center$x, state.center$y),
 "+proj=lcc +lat_1=48 +lat_2=33 +lon_0=-100 +ellps=WGS84")
res1 <- project(res, "+proj=lcc +lat_1=48 +lat_2=33 +lon_0=-100 +ellps=WGS84",
 inv=TRUE)
summary(res1 - cbind(state.center$x, state.center$y))
plot(cbind(state.center$x, state.center$y), asp=1, type="n")
text(cbind(state.center$x, state.center$y), state.abb)
plot(res, asp=1, type="n")
text(res, state.abb)
crds <- matrix(data=c(9.05, 48.52), ncol=2)
a <- project(crds, paste("+proj=ob_tran +o_proj=longlat",
 "+o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +ellps=sphere +no_defs"),
 use_ob_tran=TRUE)
a
#should be (-5.917698, -1.87195)
project(a, paste("+proj=ob_tran +o_proj=longlat",
 "+o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +ellps=sphere +no_defs"),
 inv=TRUE, use_ob_tran=TRUE)
#added after posting by Martin Ivanov
#
getPROJ4VersionInfo()
# Test for UTM == TMERC (<= 4.9.2) or UTM == ETMERC (> 4.9.2)
nhh <- matrix(c(5.304234, 60.422311), ncol=2)
nhh_utm_32N_P4 <- project(nhh, "+init=epsg:3044")
nhh_tmerc_P4 <- project(nhh, 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 <- project(nhh, 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(nhh_utm_32N_P4, nhh_tmerc_P4, tolerance=1e-9, scale=1)
# UTM == TMERC: PROJ4 <=4.9.2
all.equal(nhh_utm_32N_P4, nhh_etmerc_P4, tolerance=1e-9, scale=1)
# UTM == ETMERC: PROJ4 > 4.9.2
unis <- matrix(c(15.653453, 78.222504), ncol=2)
unis_utm_33N_P4 <- project(unis, "+init=epsg:3045")
unis_tmerc_P4 <- project(unis, 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 <- project(unis, 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(unis_utm_33N_P4, unis_tmerc_P4, tolerance=1e-9, scale=1)
# UTM == TMERC: PROJ4 <=4.9.2
all.equal(unis_utm_33N_P4, unis_etmerc_P4, tolerance=1e-9, scale=1)
# UTM == ETMERC: PROJ4 > 4.9.2
# available projections and their inverses if provided
# For >=4.9.3 returns non-finite points rather than needing crash protection
getPROJ4VersionInfo()
projs <- as.character(projInfo()$name)
res <- logical(length(projs))
names(res) <- projs
msgs <- character(length(projs))
names(msgs) <- projs
owarn <- options("warn")$warn
options(warn=2L)
for (i in seq(along=res)) {
  iprs <- paste("+proj=", projs[i], sep="")
  xy <- try(project(cbind(0, 0), iprs, legacy=TRUE), silent=TRUE)
  if (class(xy) == "try-error") {
    res[i] <- NA
    msgs[i] <- paste("fwd:", strsplit(xy, "\n")[[1]][2])
  } else {
    out <- try(project(xy, iprs, inv=TRUE, legacy=TRUE), silent=TRUE)
    if (class(out) == "try-error") {
      res[i] <- NA
      msgs[i] <- paste("inv:", strsplit(out, "\n")[[1]][2])
    } else res[i] <- isTRUE(all.equal(cbind(0,0), out))
  }
}
options(warn=owarn)
df <- data.frame(res=unname(res), msgs=unname(msgs), row.names=names(res))
# projection and inverse projection failures
# fwd: missing parameters
# inv: mostly inverse not defined
df[is.na(df$res),]
# inverse not equal to input
# (see http://lists.maptools.org/pipermail/proj/2011-November/006015.html)
df[!is.na(df$res) & !df$res,]
# inverse equal to input
row.names(df[!is.na(df$res) & df$res,])
# }