oce (version 0.9-18)

mapTissot: Plot Tissot indicatrices

Description

Plot ellipses at grid intersection points, as a method for indicating the distortion inherent in the projection [1].

Usage

mapTissot(grid=rep(15, 2), scale=0.2, ...)

Arguments

grid

numeric vector of length 2, specifying the increment in longitude and latitude for the grid. Indicatrices are drawn at e.g. longitudes seq(-180, 180, grid[1]).

scale

scale factor for ellipses. This is multiplied by min(grid) and the result is the radius of the circle on the earth, in latitude degrees.

...

extra arguments passed to plotting functions, e.g. col="red" yields red indicatrices.

Details

The purpose and interpretation are outline in [1], but should also be self-explanatory.

References

1. Snyder, John P., 1987. Map Projections: A Working Manual. USGS Professional Paper: 1395 (available at pubs.usgs.gov/pp/1395/report.pdf).

See Also

See mapPlot for general information on plotting maps, including other functions.

Examples

library(oce)
data(coastlineWorld)
par(mfrow=c(1,1), mar=c(2, 2, 1, 1))
p  <- "+proj=aea +lat_1=10 +lat_2=60 +lon_0=-45"
mapPlot(coastlineWorld, projection=p, fill="gray",
        longitudelim=c(-90,0), latitudelim=c(0,50))
mapTissot(c(15, 15), col='red')