R: Circle Polygon (on Earth)

circle.polygon {swfscMisc} | R Documentation

## Circle Polygon (on Earth)

### Description

Creates a circular polygon (optionally on the earth) centered at a given point with a constant radius.

### Usage

    circle.polygon(x, y, radius, brng.limits = 0, sides = 1, by.length = TRUE,
      units = "nm", ellipsoid = datum(), dist.method = "lawofcosines",
      destination.type = "ellipsoid", poly.type = "cart.earth")

### Arguments

`x, y` | number specifying the coordinates of the center of the circle in decimal degrees. If `poly.type` is "simple.earth" or "complex.earth", this will be longitude and latitude respectively.
`radius` | radius of sphere.
`brng.limits` | number, or vector of two numbers. If one value is given, it is used as the starting bearing in degrees for the first point of the circle. If a vector of two values is given, then they are used as the start and end bearings of arc.
`sides` | number that represents either length of sides or number of sides, as specified by the 'by.length' argument.
`by.length` | logical. If `TRUE`, then `sides` is the length of sides, if `FALSE`, then `sides` is number of sides.
`units` | character for units of distance: Can be "km" (kilometers), "nm" (nautical miles), "mi" (statute miles).
`ellipsoid` | ellipsoid model parameters as returned from a call to `datum`.
`dist.method` | character specifying method for calculating distance for `type` = "cart.earth". See `method` argument of `distance` for more information.
`destination.type` | character specifying type of surface for `type` = "gc.earth". See `type` argument of `destination` for more information.
`poly.type` | character specifying the type of polygon calculation to use. Can be one of "cartesian" using basic cartesian coordinates, "cart.earth" for a simple polygon on the earth's surface treating latitude and longitude as cartesian coordinates, or "gc.earth" for a more precise calculation keeping a constant great-circle radius.

### Value

A matrix representing the desired circle polygon centered at lat, lon of radius.

### Author(s)

Eric Archer eric.archer@noaa.gov

### Examples

    cart.earth <- circle.polygon(-117.24, 32.86, 40, poly.type = "cart.earth")

    lat.range <- c(32, 34)
    lon.range <- c(-118.5, -116)

    op <- par(mar = c(3, 5, 5, 5) + 0.1, oma = c(1, 1, 1, 1))

    map("worldHires", fill = TRUE, col = "wheat3", xlim = lon.range, ylim = lat.range)
    points(-117.24, 32.86, pch = 19, col = "red")
    polygon(cart.earth, border = "red", lwd = 3)
    lat.lon.axes(n = 3)
    box(lwd = 2)
    mtext("poly.type = 'cart.earth'", line = 3)

    par(op)

[Package swfscMisc version 1.2 Index]