transform {proj4}R Documentation

Transform geographic coordinates from one projection into another

Description

Transformation of geographics coordinates from one projection to another, using PROJ.4 library.

Usage

ptransform(data, src.proj, dst.proj, silent=TRUE)

Arguments

data

input (list, matrix or 2d-array) - see details below.

src.proj

description of the source projection

dst.proj

description of the destination projection

silent

if set to TRUE, warnings will be suppressed

Details

The data can be a list of vectors (if the list contains more than three entries, only first three entries are used and a warning is issued), a two-dimensional matrix or array (the number of columns or rows must be at most three). If the input is a list then the result will be a list with the entries named x, y and z, otherwise the result is a matrix with three columns.

When the list form is used, inputs are recycled with a warning when necessary. All unspecified coordinates are set to zero.

Note that the project specification must include an ellipsoid or a datum. Add ellps='sphere' to obtain the same result as older PROJ.4 versions with no datum specification.

Datum files must be installed in order to be able to perform datum shifts (on Windows they should be located in c:\proj) - see PROJ.4 website for the download of datum files.

A list of some commonly used projections can be found at http://www.remotesensing.org/geotiff/proj_list/,

Value

A matrix with three columns or list with projected coordinates. If the input was a list then the output will be a list, otherwise a matrix.

Author(s)

Simon Urbanek

References

http://www.remotesensing.org/proj/

Examples

data(state)
sc <- cbind(state.center$x, state.center$y)
## this is essentially the same as project except
## that the default lat/long input is in radians
tr <- ptransform(sc/180*pi, '+proj=latlong +ellps=sphere',
                 '+proj=merc +ellps=sphere')
## we can compare it with the project result
res <- project(sc, c(proj="merc"))
## ptransform has z coordinate which is 0 for this projection
summary(tr - cbind(res, 0))

[Package proj4 version 1.0-9 Index]