meters.per.degree.lon: Convert degrees longitude to meters East-West.

In ejanalysis/proxistat: Create a Proximity Score in Each Census Unit, Based on Distances to Specified Points (as in EPA's EJScreen tool, for example)

Convert degrees longitude to meters East-West.

Description

meters.per.degree.lon returns meters traveled East-West per decimal degree longitude, given latitude (Northern Hemisphere).

Usage

meters.per.degree.lon(theta)

Arguments

theta

The decimal degrees of latitude of the Northern Hemisphere location(s) of interest, as number or vector of numbers.

Details

This function returns the meters traveled East-West per decimal degree longitude, at a given latitude (Northern Hemisphere). This is an approximation and is less accurate further from the given latitude. Based on http://en.wikipedia.org/wiki/Latitude#Length_of_a_degree_of_latitude and
http://en.wikipedia.org/wiki/Longitude#Length_of_a_degree_of_longitude

Input theta is latitude on WGS84. Function is as follows:
theta.r <- 0.01745329 * theta
ecc2 <- 0.00669438
return( 20037508 * cos(theta.r) / ( 180 * sqrt(1- ecc2 * (sin(theta.r))^2 ) ) )
Based on the following calculations:
The equatorial.radius used is 6378137.0 in meters
2 pi / 360 = 0.01745329
for the WGS84 ellipsoid with a = 6,378,137.0 m and b = 6,356,752.3142 m.
equatorial.radius <- 6378137.0 # a in meters
b=6356752.3142
ecc2 <- (equatorial.radius^2 - b^2)/equatorial.radius^2
ecc2 <- (6378137.0^2 - 6356752.3142^2) / 6378137.0^2
pi * equatorial.radius = 20037508

Also see http://en.wikipedia.org/wiki/Longitude and http://en.wikipedia.org/wiki/Decimal_degrees

Value

Returns meters traveled East-West per decimal degree longitude, as a number or vector of numbers the same length as the input.

See Also

meters.per.degree.lat for a similar function but for travel North-South, and deltalon.per.km for the inverse of this function (other than a factor of 1000), and get.distances.all and also get.distances to get distances between points, and related functions.

Examples

meters.per.degree.lon(32)
meters.per.degree.lon(c(0,45,72))

ejanalysis/proxistat documentation built on Jan. 1, 2025, 10:02 a.m.