Add Tissot Indicatrices to a Map

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Description

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

Usage

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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

numerical 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 outlined in [1], but should also be self-explanatory.

Author(s)

Dan Kelley

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

A map must first have been created with mapPlot.

Other functions related to maps: lonlat2map, lonlat2utm, map2lonlat, mapArrows, mapAxis, mapContour, mapDirectionField, mapGrid, mapImage, mapLines, mapLocator, mapLongitudeLatitudeXY, mapPlot, mapPoints, mapPolygon, mapScalebar, mapText, oceCRS, shiftLongitude, utm2lonlat

Examples

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## Not run: 
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')

## End(Not run)

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