tissot: Tissot

In mdsumner/tissot: The Tissot Indicatrix

Tissot

Description

Create the Tissot Indicatrix.

Usage

tissot(
  lambda,
  phi = NULL,
  degrees = TRUE,
  A = 6378137,
  f.inv = 298.257223563,
  ...,
  proj.in,
  proj.out
)

Arguments

lambda	longitude
phi	latitude
degrees	logical, work in degrees or radians
A	ellipsoidal semi-major axis (meters)
f.inv	the inverse flattening
...	passed to internal function
proj.in	projection of input
proj.out	projection of context

Details

Compute properties of scale distortion and Tissot's indicatrix at location x = c(lambda, phi) using prj as the projection. A is the ellipsoidal semi-major axis (in meters) and f.inv is the inverse flattening. The projection must return a vector (x, y) when given a vector (lambda, phi). (Not vectorized.) Optional arguments ... are passed to prj. Source: Snyder pp 20-26 (WGS 84 defaults for the ellipsoidal parameters). All input and output angles are in degrees.

Value

list with stuff as per below

Examples

x <- seq(-175, 175, by = 15)
y <- seq(-82.5, 82.5, by = 15)
xy <- expand.grid(x, y)
r <- tissot(xy,
            proj.in= "OGC:CRS84",
            proj.out= "+proj=robin")

j <- which.min(abs(135 - r$lon) + abs(54 - r$lat))
idx0 <- indicatrix0(r[j, ], scale=10^4, n=71)
op <- par(mfrow =   c(2, 1))
plot(idx0, add = FALSE)
idx <- indicatrix(r, scale=3e5, n=71)
plot(idx, add = FALSE)
tissot_abline(r$lon[j], r$lat[j])
par(op)

mdsumner/tissot documentation built on Jan. 16, 2024, 4:10 a.m.