Package 'tissot'

Indicatrix

Description

Indicatrix

plot indicatrix

Usage

indicatrix(x, scale = 1, ...)

## S3 method for class 'indicatrixes'
plot(
  x,
  asp = 1,
  xlab = "x",
  ylab = "y",
  add = FALSE,
  ...,
  col.base = rgb(0, 0, 0, 0.1),
  col.lambda = grey(0.75),
  col.phi = "#1b9e77",
  col.major = "#7570b3",
  col.minor = "#d95f02",
  col.outline = "black"
)

indicatrix0(x, scale = 1, ...)

## S3 method for class 'indicatrix0'
plot(
  x,
  asp = 1,
  xlab = "Easting",
  ylab = "Northing",
  add = FALSE,
  ...,
  col.base = rgb(0, 0, 0, 0.1),
  col.lambda = grey(0.75),
  col.phi = "#45A271",
  col.major = "#A782C3",
  col.minor = "#C87A8A",
  col.outline = "black"
)

Arguments

x	object from tissot
scale	scaling
...	arguments n, from and to passed to ti_ellipse function
asp	aspect ratio
xlab	x-axis labels
ylab	y-axis labels
add	add to existing plot
col.base	colour of base
col.lambda	colour of lambda
col.phi	colour of phi
col.major	major axis colour
col.minor	minor axis colour
col.outline	outline colour

Details

Reprocesses the output of tissot into convenient geometrical data.

---

Ellipse

Description

Ellipse

Usage

ti_ellipse(center, axes, scale = 1, n = 36, from = 0, to = 2 * pi)

Arguments

center	center
axes	axes
scale	scale
n	n
from	from
to	to

Value

matrix

---

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)

---

Get last plot projection

Description

'tissot_map()' will add the [world] coastline to any map.

Usage

tissot_map(..., add = TRUE)

tissot_abline(lambda, phi = NULL, ..., proj.in = NULL)

tissot_get_proj()

Arguments

...	graphical parameters for [lines()] if 'add = TRUE', or for [plot()] if 'add = FALSE'
add	logical, default 'TRUE' add to existing plot or create new
lambda	longitude at which to draw a vertical line
phi	latitude at which to draw a horizontal line
proj.in	projection for expert use

Details

'tissot_get_proj()' When the indicatrix is plotted it registers its projection. This string can be obtained with this getter function.

'tissot_abline()' will draw a vertical and horizontal line at a give longitude latitude (where they intersect is the actual lon,lat location)

Value

'tissot_map()' returns the internal world map data (projected if one is current) as a matrix

'tissot_abline()' called for its side effect of drawing on the plot

'tissot_get_proj()' returns the value of the current projection, or NULL

---

world coastline

Description

A modified matrix version of data from the maps package.

Usage

world

Format

An object of class matrix (inherits from array) with 82403 rows and 2 columns.

Details

Basically longitudes have been smooshed to 'abs(lon) < 180'

---