project.M3.to.lonlat: Project coordinates from model units to longitude/latitude

In M3: Reading M3 files

Description

Project coordinates from model units (as specified according to the projection given by a user-designated Models3-formatted file) to longitude/latitude.

Usage

project.M3.to.lonlat(x, y, file, units, ...)

Arguments

x	x-coordinates of points in model units (meters or kilometers, depeding on the value of units
y	y-coordinates of points in model units (meters or kilometers, depeding on the value of units
file	Name of Models3-formatted file with the same projection as x and y.
units	Units of x and y.
...	Other arguments to pass to get.proj.info.M3 function. In this case, the only relevant argument would be the earth radius to use for the projection in file.

Details

This function uses the function project from the package rgdal to project to longitude/latitude given the projection defined by the Models3-formatted file. Package rgdal provides the R interface to GDAL (Geospatial Data Abstraction Library, http://www.gdal.org).

Value

A list containing the elements coords and units. The element coords contains a matrix of coordinates in longitude/latitude. The element units contains the string "deg" to designate that coords is in degrees of longitude/latitude.

Author(s)

Jenise Swall

References

http://www.gdal.org

See Also

project.lonlat.to.M3, project.M3.1.to.M3.2, get.proj.info.M3

Examples

## List of state capital longitudes/latitudes
## (from http://www.xfront.com/us_states).
capitals <- data.frame(x=c(-84.39,-86.28,-81.04,-86.78,-78.64,-84.86),
                       y=c(33.76,32.36,34.00,36.17,35.77,38.20),
                       name=c("Atlanta", "Montgomery", "Columbia",
                                 "Nashville", "Raleigh", "Frankfort")
                        )
## Plot these on a map, with state lines.
plot(capitals$x, capitals$y)
map("state", add=TRUE)

## Now, put these on the same Lambert conic conformal projection used
## in the demo file below.
lcc.file <- system.file("extdata/ozone_lcc.ncf", package="M3")
lcc.capitals <- project.lonlat.to.M3(capitals$x, capitals$y, lcc.file)

## Now, project them back to longitude/latitude, make sure we get the
## same thing we started with.
chk.capitals <- project.M3.to.lonlat(lcc.capitals$coords[,"x"],
                                     lcc.capitals$coords[,"y"],
                                     lcc.file,
                                     units=lcc.capitals$units)
## These differences should be 0 or something very tiny.
summary(capitals[,c("x", "y")] - chk.capitals$coords)

M3 documentation built on May 2, 2019, 11:04 a.m.